Forde had found the year before in the blood of a patient suffering from
a peculiar type of fever in Gambia. In 1902-1903 Castellani found the
same parasite in the cerebro-spinal fluid of sleeping-sickness patients
and definitely reported it as the causative organism of the disease. His
work soon found abundant confirmation, and it was discovered that the
sleeping sickness was but the ultimate phase of the fever discovered by
Dutton and Forde.
When Castellani made known his discovery of the trypanosome of sleeping
sickness, Brumpt, in France, and Sambon, in England, independently
advanced the theory that the disease was transmitted by the tsetse-fly,
_Glossina palpalis_. This theory was based upon the geographical
distribution and epidemiology of the disease. Since then it has been
abundantly verified by experimental evidence.
Fortunately for the elucidation of problems relating to the methods of
transfer of sleeping sickness, _Trypanosoma gambiense_ is pathogenic for
many species of animals. In monkeys it produces symptoms very similar to
those caused in man. Bruce early showed that _Glossina palpalis_ "fed on
healthy monkeys eight, twelve, twenty-four and forty-eight hours after
having fed on a native suffering from trypanosomiasis, invariably
transmitted the disease. After three days the flies failed to transmit
it." In his summary in Osler's Modern Medicine, he continues "But this
is not the only proof that these flies can carry the infective agent. On
the lake shore there was a large native population among whom we had
found about one-third to be harboring trypanosomes in their blood. The
tsetse-flies caught on this lake shore, brought to the laboratory in
cages, and placed straightway on healthy monkeys, gave them the disease
in every instance, and furnished a startling proof of the danger of
loitering along the lake shore among those infected flies."
As in the case of nagana, Bruce and most of the earlier investigators
supposed the transmission of the sleeping sickness trypanosome by
_Glossina palpalis_ to be purely mechanical. The work of Kleine (1909)
clearly showed that for _Trypanosoma gambiense_ as well as for
_Trypanosoma brucei_ the fly served as an essential host. Indeed, Kleine
and many subsequent investigators are inclined to think that there is
practically no mechanical transmission of trypanosomes from animal to
animal by _Glossina_ in nature, and that the many successful experiments
of the earlier investigators were due to the fact that they used wild
flies which already harbored the transformed parasite rather than
directly inoculated it from the blood of the diseased experimental
animals. While the criticism is applicable to some of the work, this
extreme view is not fully justified by the evidence at hand.
Kleine states (1912) that _Glossina palpalis_ can no longer be regarded
as the sole transmitter of sleeping sickness. Taute (1911) had shown
that under experimental conditions _Glossina morsitans_ was capable of
transferring the disease and Kleine calls attention to the fact that in
German East Africa, in the district of the Rovuma River, at least a
dozen cases of the disease have occurred recently, though only _Glossina
morsitans_ exists in the district. It appears, however, that these cases
are due to a different parasite, _Trypanosoma rhodesiense_. This
species, found especially in north-east Rhodesia and in Nyassaland, is
transferred by _Glossina morsitans_.
Other workers maintain that the disease may be transmitted by various
blood-sucking flies, or even bugs and lice which attack man. Fulleborn
and Mayer (1907) have shown by conclusive experiments that _Aedes
(Stegomyia) calopus_ may transmit it from one animal to another if the
two bites immediately succeed each other.
It is not possible that insects other than the tsetse-flies (and only
certain species of these), play an important role in the transmission of
the disease, else it would be much more wide-spread. Sambon (1908)
pointed out that the hypothesis that is spread by _Aedes calopus_ is
opposed by the fact that the disease never spread in the Antilles,
though frequently imported there by West African slaves. The same
observation would apply also to conditions in our own Southern States in
the early part of the past century.
Since _Glossina palpalis_ acts as an essential host of the parasite and
the chief, if not the only, transmitter, the fight against sleeping
sickness, like that against malaria and yellow fever, becomes primarily
a problem in economic entomology. The minutest detail of the
life-history, biology, and habits of the fly, and of its parasites and
other natural enemies becomes of importance in attempts to eradicate the
disease. Here we can consider only the general features of the subject.
_Glossina palpalis_ lives in limited areas, where the forest and
undergrowth is dense, along the lake shore or river banks. According to
Hodges, the natural range from shore is under thirty yards, though the
distance to which the flies may follow man greatly exceed this.
It is a day feeder, a fact which may be taken advantage of in avoiding
exposure to its attacks. The young are brought forth alive and
full-grown, one every nine or ten days. Without feeding, they enter the
ground and under favorable conditions, complete their development in a
month or more.
[Illustration: 137. Sleeping sickness concentration camp in German East
Africa. Report of German Commission.]
Methods of control of the disease must look to the prevention of
infection of the flies, and to their avoidance and destruction. Along
the first line, much was hoped from temporary segregation of the sick in
regions where the fly was not found. On the assumption that the flies
acted as carriers only during the first two or three days, it was
supposed that even the "fly belts" would become safe within a few days
after the sick were removed. The problem was found to be a much more
difficult one when it was learned that after a given brief period the
fly again became infective and remained so for an indeterminate period.
Nevertheless, isolation of the sick is one of the most important
measures in preventing the spread of the disease into new districts.
Much, too, is being accomplished by moving native villages from the fly
belts. (c.f. fig. 137.)
All measures to avoid the flies should be adopted. This means locating
and avoiding the fly belts as far as possible, careful screening of
houses, and protection of the body against bites.
Clearing the jungle along the water courses for some yards beyond the
natural range of the fly has proved a very important measure. Castellani
recommends that the area be one hundred yards and around a village three
hundred yards at least.
Detailed studies of the parasites and the natural enemies of the
tsetse-fly are being undertaken and may ultimately yield valuable
results.
SOUTH AMERICAN TRYPANOSOMIASIS--The tsetse-flies are distinctively
African in distribution and until recently there were no trypanosomes
known to infest man in America. In 1909 Dr. Chagas, of Rio de Janeiro
described a new species, _Trypanosoma cruzi_, pathogenic to man.
_Trypanosoma cruzi_ is the causative organism of a disease common in
some regions of Brazil, where it is known as "opilacao." It is
especially to be met with in children and is characterized by extreme
anemia, wasting, and stunted development associated with fever, and
enlargement of the thyroid glands. The disease is transmitted by the
bites of several species of assassin-bugs, or Reduviidae, notably by
_Conorhinus megistus_. The evolution of the parasite within the bug has
been studied especially by Chagas and by Brumpt. From the latter's text
we take the following summary.
The adult trypanosomes, ingested by a _Conorhinus megistus_, of any
stage, first change into Crithidia-like forms and then those which
remain in the stomach become ovoid and non-motile. Brumpt found these
forms in immense numbers, in a _Conorhinus_ which had been infested
fourteen months before. The forms which pass into the intestine quickly
assume the _Crithidia_ form and continue to develop rapidly under this
form. Some weeks later they evolve into the trypanosome forms,
pathogenic for man. They then pass out with the excrement of the bug and
infect the vertebrate host as soon as they come in contact with any
mucous layer (buccal, ocular or rectal). More rarely they enter through
the epidermis.
Brumpt showed that the development could take place in three species;
bed-bugs (_Cimex lectularius_, _C. hemipterus_) and in the tick
_Ornithodoros moubata_. The evolution proceeds in the first two species
of bed-bugs as rapidly as in Conorhinus, or even more rapidly, but they
remain infective for a much shorter time and hence Brumpt considers that
they play a much less important role in the spread of the disease.
_Conorhinus megistus_, like related forms in our Southern States, very
commonly frequents houses and attacks man with avidity. Chagas states
that the bites are painless and do not leave any traces. They are
usually inflicted on the lips, or the cheeks and thus the buccal mucosa
of a sleeper may be soiled by the dejections of the insect and the bite
serving as a port of entry of the virus, remain unnoticed.
The possibility of some of our North American Reduviidae playing a
similar role in the transmission of disease should not be overlooked.
LEISHMANIOSES AND INSECTS--Closely related to the trypanosomes is a
group of intracellular parasites which have recently been grouped by
Ross under the genus _Leishmania_. Five species are known to affect man.
Three of these produce local skin infestations, but two of them,
_Leishmania donovani_ and _L. infantum_, produce serious and often fatal
systemic diseases.
The first of these, that produced by _L. donovani_, is an exceedingly
virulent disease common in certain regions of India and China. It is
commonly known as "Kala-azar," or "dum-dum" fever, and more technically
as tropical leishmaniasis. Patton (1907) believes that the parasite is
transmitted by the bed-bug _Cimex hemipterus_, and has described a
developmental cycle similar to that which can be found in artificial
cultures. On the other hand, Donovan was unable to confirm Patton's work
and believes that the true intermediate host is a Reduviid bug,
_Conorhinus rubrofasciatus_.
_Leishmania infantum_ is the cause of the so-called infantile splenic
leishmaniasis, occurring in northern Africa, Spain, Portugal, Italy, and
possibly other parts of Europe. The parasite occurs habitually in the
dog and is only accidentally transferred to children. Alvares and da
Silva, in Portugal (according to Brumpt, 1913) have found that the
excrement of a flea from a diseased dog contains flagellates, and they
suggest that the infection may be transmitted by the accidental
inoculation of this excrement by means of the proboscis of the flea, as
has been thought to occur in the case of the plague. To this Brumpt
objects that they and other workers who thought to trace the development
of _Leishmania infantum_ were apparently misled by the presence of a
harmless _Herpetomonas_ which infests dog fleas in all countries, even
where the leishmaniasis is unknown.
Basile (1910 and 1911) however, carried on numerous experiments
indicating that the disease was transferred from children to dogs and
from dog to dog by the dog flea, and was able to find in the tissues of
the insects forms perfectly identical with those found in children and
in dogs suffering from leishmaniasis. He also found that _Pulex
irritans_ was capable of acting as the carrier.
Of the cutaneous type of leishmaniasis, the best known is the so-called
"Oriental sore," an ulcerative disease of the skin which is epidemic in
many tropical and subtropical regions. The causative organism is
_Leishmania tropica_, which occurs in the diseased tissues as bodies
very similar to those found in the spleen in cases of Kala-azar. The
disease is readily inoculable and there is no doubt that it may be
transferred from the open sores to abraded surfaces of a healthy
individual by house-flies. It is also believed by a number of
investigators that it may be transferred and directly inoculated by
various blood-sucking insects.
TICKS AND DISEASES OF MAN AND ANIMALS
We have seen that the way to the discoveries of the relations of
arthropods to disease was pointed out by the work of Leuckart and
Melnikoff on the life cycle of _Dipylidium_, and of Fedtschenko and
Manson on that of _Filaria_. They dealt with grosser forms, belonging to
well-recognized parasitic groups.
This was long before the role of any insect as a carrier of pathogenic
micro-organisms had been established, and before the Protozoa were
generally regarded as of importance in the causation of disease. The
next important step was taken in 1889 when Smith and Kilbourne
conclusively showed that the so-called Texas fever of cattle, in the
United States, is due to an intracorpuscular blood parasite transmitted
exclusively by a tick. This discovery, antedating by eight years the
work on the relation of the mosquito to malaria, had a very great
influence on subsequent studies along these lines.
While much of the recent work has dealt with the true insects, or
hexapods, it is now known that several of the most serious diseases of
animals, and at least two important diseases of man are tick borne.
These belong to the types known collectively as _babesioses_ (or
"_piroplasmoses_"), and _spirochaetoses_.
The term _babesiosis_ is applied to a disease of man or animals which is
caused by minute protozoan parasites of the genus _Babesia_, living in
the red blood corpuscles. These parasites have usually been given the
generic name _Piroplasma_ and hence the type of disease which they cause
is often referred to as "_piroplasmosis_." The best known illustration
is the disease known in this country as Texas fever of cattle.
CATTLE TICKS AND TEXAS FEVER--The cattle disease, which in the United
States is known as Texas fever, is a widely distributed, exceedingly
acute disease. In Australia it is known as _redwater fever_ and in
Europe as haemoglobinuria, due to the fact that the urine of the diseased
animals is discolored by the breaking down of the red blood corpuscles
infested by the parasite.
In their historical discussion, Smith and Kilbourne, point out that as
far back as 1796 it was noted that Southern cattle, in a state of
apparent health, might spread a fatal disease among Northern herds. As
observations accumulated, it was learned that this infection was carried
only during the warm season of the year and in the depth of winter
Southern cattle were harmless. Moreover, Southern cattle after remaining
for a short time in the North lost their power to transmit the disease,
and the same was true of cattle which had been driven for a considerable
distance.
Very significant was the fact that the infection was not communicated
directly from the Southern to Northern cattle but that the ground over
which the former passed was infected by them, and that the infection was
transmitted thence to susceptible cattle _after a period of not less
than thirty days had elapsed_.
Of course a disease as striking as this, and which caused such enormous
losses of cattle in the region invaded was fruitful in theories
concerning its causation. The most widespread was the belief that
pastures were infected by the saliva, urine, or manure of Southern
cattle. There were not wanting keen observers who suggested that the
disease was caused by ticks, but little weight was given to their view.
Various workers had described bacteria which they had isolated from the
organs of the diseased animals, but their findings could not be
verified. In 1889, Smith and Kilbourne discovered a minute, pear-shaped
organism (fig. 138) in the red blood corpuscles of a cow which had
succumbed to Texas fever. On account of their shape they were given the
generic name _Pyrososma_ and because they were usually found two in a
corpuscle, the specific name, _bigeminum_. It is now generally accepted
that the parasite is the same which Babes had observed the year before
in Roumanian cattle suffering from haemoglobinuria, and should be known
as _Babesia bovis_ (Babes).
[Illustration: 138. Babesia bovis in blood corpuscles. After Calli.]
[Illustration: 139. The cattle tick (Boophilus annulatus). (_a_) Female;
(_b_) male. After Comstock.]
By a series of perfectly conclusive experiments carried on near
Washington, D.C., Smith and Kilbourne showed that this organism was
carried from Southern cattle to non-immune animals by the so-called
Southern cattle tick, _Boophilus annulatus_ (= _Margaropus annulatus_)
(fig. 139).
Of fourteen head of native cattle placed in a field with tick-infested
Northern cattle all but two contracted the disease. This experiment was
repeated with similar results. Four head of native cattle kept in a plot
with three North Carolina cattle which had been carefully freed from
ticks remained healthy. A second experiment the same year gave similar
results.
Still more conclusive was the experiment showing that fields which had
not been entered by Southern cattle but which had been infected by
mature ticks taken from such animals would produce Texas fever in native
cattle. On September 13, 1889, several thousand ticks collected from
cattle in North Carolina three and four days before, were scattered in a
small field near Washington. Three out of four native animals placed in
this field contracted the disease. The fourth animal was not examined as
to its blood but it showed no external symptoms of the disease.
[Illustration: 140. Hyalomma aegypticum. After Nuttall and Warburton.]
In these earlier experiments it was believed that the cattle tick acted
as a carrier of the disease between the Southern cattle and the _soil_
of the Northern pastures. "It was believed that the tick obtained the
parasite from the blood of its host and in its dissolution on the
pasture a certain resistant spore form was set free which produced the
disease when taken in with the food." The feeding of one animal for some
time with grass from the most abundantly infected field, without any
appearance of the disease, made this hypothesis untenable.
In the experimental work in 1890 the astonishing fact was brought out
that the disease was conveyed neither by infected ticks disintegrating
nor by their directly transferring the parasite, but that it was
conveyed by the young hatched from eggs of infected ticks. In other
words, the disease was hereditarily transferred to ticks of the second
generation and they alone were capable of conveying it.
Thus was explained the fact that Texas fever did not appear immediately
along the route of Southern cattle being driven to Northern markets but
that after a certain definite period it manifested itself. It was
conveyed by the progeny of ticks which had dropped from the Southern
cattle and deposited their eggs on the ground.
These results have been fully confirmed by workers in different parts of
the world,--notably by Koch, in Africa, and by Pound, in Australia.
The disease is apparently transmitted by _Boophilus annulatus_ alone, in
the United States, but it, or an almost identical disease, is conveyed
by _Ixodes hexagonus_ in Norway, _Ixodes ricinus_ in Finland and France
and by the three species, _Boophilus decoloratus_, _Hyalomma aegypticum_
(fig. 140 and 141), and _Haemaphysalis punctata_ in Africa.
[Illustration: 141. Hyalomma aegypticum. Capitulum of female; (_a_)
dorsal, (_b_) ventral aspect.]
In spite of the detailed study which it has received, the life cycle of
_Babesia bovis_ has not been satisfactorily worked out. The asexual
reproduction in the blood of the vertebrate host has been described but
the cycle in the tick is practically unknown.
More successful attempts have been made to work out the life cycle of a
related species, _Babesia canis_, which causes malignant jaundice in
dogs in Africa and parts of Southern Europe. In this instance, also, the
disease is transmitted by heredity to the ticks of the second
generation. Yet the larval, or "seed ticks," from an infected female are
not capable of conveying the disease, but only the nymphs and adults.
Still more complicated is the condition in the case of _Babesia ovis_ of
sheep, which Motas has shown can be conveyed solely by the adult,
sexually mature ticks of the second generation.
In _Babesia canis_, Christopher (1907) observed developmental stages in
the tick. He found in the stomach of adult ticks, large motile
club-shaped bodies which he considered as ookinetes. These bodies pass
to the ovaries of the tick and enter the eggs where they become globular
in form and probably represent an oocyst. This breaks up into a number
of sporoblasts which enter the tissues of the developing tick and give
rise to numerous sporozoites, which collect in the salivary glands and
thence are transferred to the vertebrate host. A number of other species
of _Babesia_ are known to infest vertebrates and in all the cases where
the method has been worked out it has been found that the conveyal was
by ticks. We shall not consider the cases more fully here, as we are
concerned especially with the method of transfer of human diseases.
TICKS AND ROCKY MOUNTAIN SPOTTED FEVER OF MAN--Ever since 1873 there has
been known in Montana and Idaho a peculiar febrile disease of man, which
has gained the name of "Rocky Mountain spotted fever." Its onset is
marked by chills and fever which rapidly become acute. In about four to
seven days there appears a characteristic eruption on the wrists, ankles
or back, which quickly covers the body.
McClintic (1912) states that the disease has now been reported from
practically all of the Rocky Mountain States, including Arizona,
California, Colorado, Idaho, Montana, Nevada, Oregon, Utah, Washington,
and Wyoming. "Although the disease is far more prevalent in Montana and
Idaho than in any of the other States, its spread has assumed such
proportions in the last decade as to call for the gravest consideration
on the part of both the state and national health authorities. In fact,
the disease has so spread from state to state that it has undoubtedly
become a very serious interstate problem demanding the institution of
measures for its control and suppression."
A peculiar feature of the Rocky Mountain spotted fever is a marked
variation in its severity in different localities. In Montana, and
especially in the famous Bitter Root Valley, from 33 per cent to 75 per
cent of the cases result fatally. On the other hand, the fatality does
not exceed four per cent in Idaho.
In 1902, Wilson and Chowning reported the causative organism of spotted
fever to be a blood parasite akin to the _Babesia_ of Texas fever, and
made the suggestion that the disease was tick-borne. The careful studies
of Stiles (1905) failed to confirm the supposed discovery of the
organism, and the disease is now generally classed as due to an
invisible virus. On the other hand, the accumulated evidence has fully
substantiated the hypothesis that it is tick-borne.
According to Ricketts (1907) the experimental evidence in support of
this hypothesis was first afforded by Dr. L. P. McCalla and Dr. H. A.
Brereton, in 1905. These investigators transmitted the disease from man
to man in two experiments. "The tick was obtained 'from the chest of a
man very ill with spotted fever' and 'applied to the arm of a man who
had been in the hospital for two months and a half, and had lost both
feet from gangrene due to freezing.' On the eighth day the patient
became very ill and passed through a mild course of spotted fever,
leaving a characteristic eruption. The experiment was repeated by
placing the tick on a woman's leg and she likewise was infected with
spotted fever."
The most detailed studies were those of the late Dr. H. T. Ricketts, and
it was he who clearly established the tick hypothesis. In the summer of
1906 he found that guinea pigs and monkeys are very susceptible to
spotted fever and can readily be infected by inoculation of blood from
patients suffering from the disease. This opened the way to experimental
work on tick transmission. A female tick was fed upon an infected guinea
pig for two days, removed and isolated for two days and then placed upon
a healthy guinea pig. After an incubation period of three and a half
days the experimental animal contracted a well-marked case of the
disease.
A similar result was obtained at the same time by King, and later in the
season Ricketts proved that the male tick was also capable of
transmitting the disease. He found that there was a very intimate
relation of the virus to the tick and that the transmission must be
regarded as biological throughout. Ticks remained infective as long as
they lived and would feed for a period of several months. If they
acquired the disease in the larval or nymphal stage they retained it
during molting and were infective in the subsequent stages. In a few
cases the larvae from an infected female were infective.
The evidence indicated that the tick suffers from a relatively harmless,
generalized infection and the virus proliferates in its body. The
disease probably is transferred through the salivary secretion of the
tick since inoculation experiments show that the salivary glands of the
infected adult contain the virus.
It is probable that in nature the reservoir of the virus of spotted
fever is some one or more of the native small animals. Infected ticks
have been found in nature, and as various wild animals are susceptible
to the disease, it is obvious that it may exist among them unnoticed.
Wilson and Chowning suggested that the ground squirrel plays the
principal role.
Unfortunately, much confusion exists regarding the correct name of the
tick which normally conveys the disease. In the medical literature it is
usually referred to as _Dermacentor occidentalis_, but students of the
group now agree that it is specifically distinct. Banks has designated
it as _Dermacentor venustus_ and this name is used in the publications
of the Bureau of Entomology. On the other hand, Stiles maintains that
the common tick of the Bitter Root Valley, and the form which has been
collected by the authors who have worked on Rocky Mountain spotted fever
in that region, is separable from _D. venustus_, and he has described it
under the name of _Dermacentor andersoni_.
Mayer (1911) has shown experimentally that spotted fever may be
transmitted by several different species of ticks, notably _Dermacentor
marginatus_, _Dermacentor variabilis_ and _Amblyomma americanum_. This
being the case, the question of the exact systematic status of the
species experimented upon in the Bitter Root Valley becomes less
important, for since _Dermacentor occidentalis_, _Dermacentor venustus_
and _Dermacentor andersoni_ all readily attack man, it is probable that
either species would readily disseminate the disease if it should spread
into their range.
Hunter and Bishop (1911) have emphasized the fact that in the eastern
and southern United States there occur several species which attack man,
and any one of which might transmit the disease from animal to animal
and from animal to man. The following species, they state, would
probably be of principal importance in the Southern and Eastern States:
the lone star tick (_Amblyomma americanum_); the American dog tick
(_Dermacentor variabilis_); and the gulf-coast tick (_Amblyomma
maculatum_). In the extreme southern portions of Texas, _Amblyomma
cajennense_, is a common pest of man.
Since the evidence all indicates that Rocky Mountain spotted fever is
transmitted solely by the tick, and that some of the wild animals serve
as reservoirs of the virus, it is obvious that personal prophylaxis
consists in avoiding the ticks as fully as possible, and in quickly
removing those which do attack. General measures along the line of tick
eradication must be carried out if the disease is to be controlled. That
such measures are feasible has been shown by the work which has been
done in controlling the tick-borne Texas fever of cattle, and by such
work as has already been done against the spotted fever tick, which
occurs on both wild and domestic animals. Detailed consideration of
these measures is to be found in the publications of the Public Health
and Marine Hospital Service, and the Bureau of Entomology. Hunter and
Bishopp give the following summarized recommendations for control or
eradication measures in the Bitter Root Valley.
(1) A campaign of education, whereby all the residents of the valley
will be made thoroughly familiar with the feasibility of the plan of
eradication, and with what it will mean in the development of the
valley.
(2) The obtaining of legislation to make it possible to dip or oil all
live stock in the Bitter Root Valley.
(3) The obtaining of an accurate census of the horses, cattle, sheep,
mules, and dogs in the valley.
(4) The construction of ten or more dipping vats.
(5) The providing of materials to be used in the dipping mixture.
(6) The organization of a corps of workers to carry on the operations.
(7) The systematic dipping of the horses, cattle, sheep, and dogs of the
valley on a definite weekly schedule from approximately March 10 to June
9.
(8) The treatment by hand of the animals in localities remote from vats,
on the same schedule.
They estimate that after three seasons' operations a very small annual
expenditure would provide against reinfestation of the valley by the
incoming of cattle from other places.
Supplementary measures consist in the killing of wild mammals which may
harbor the tick; systematic burning of the brush and debris on the
mountain side; and in clearing, since the tick is seldom found on land
under cultivation.
CHAPTER X
ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA [_Continued_]
ARTHROPODS AND SPIROCHAETOSES OF MAN AND ANIMALS
The term spirochaetoses is applied to diseases of man or animals which
are due to protistan parasites belonging to the group of slender, spiral
organisms known as spirochaetes.
There has been much discussion concerning the relationship Of the
spirochaetes. Formerly, they were regarded as bacteria closely related to
the forms grouped in the genus _Spirillum_. The results of the detailed
study which the spirochaetes have received in recent years, have led most
of the workers to consider them as belonging to the protozoa. The merits
of the discussion we are not concerned with here, but rather with the
fact that a number of diseases caused by spirochaetes are
arthropod-borne. The better known of these we shall discuss.
AFRICAN RELAPSING FEVER OF MAN--It has long been known to the natives of
Africa and to travelers in that country, that the bite of a certain
tick, _Ornithodoros moubata_, may be followed by severe or even fatal
fever of the relapsing type. Until recent years, it was supposed that
the effect was due to some special virulence of the tick, just as nagana
of cattle was attributed to the direct effect of the bite of the
tsetse-fly. The disease is commonly known as "tick-fever" or by the
various native names of the tick.
In 1904, Ross and Milne, in Uganda, and Dutton and Todd on the Congo,
discovered that the cause of the disease is a spirochaete which is
transmitted by the tick. This organism has been designated by Novy and
Knapp as _Spirochaeta duttoni_.
_Ornithodoros moubata_ (fig. 142), the carrier of African relapsing
fever, or "tick-fever," is widely distributed in tropical Africa, and
occurs in great numbers in the huts of natives, in the dust, cracks and
crevices of the dirt floors, or the walls. It feeds voraciously on man
as well as upon birds and mammals. Like others of the _Argasidae_, it
resembles the bed-bug in its habit of feeding primarily at night. Dutton
and Todd observed that the larval stage is undergone in the egg and that
the first free stage is that of the octopod nymph.
[Illustration: 142. Ornithodoros moubata. (_a_) Anterior part of venter;
(_b_) second stage nymph; (_c_) capitulum; (_d_) dorsal and (_e_)
ventral aspect of female; (_f_) ventral aspect of nymph; (_g_) capitulum
of nymph. After Nuttall and Warburton.]
The evidence that the fever is transmitted by this tick is conclusive.
Koch found that from five per cent to fifteen per cent, and in some
places, fifty per cent of the ticks captured, harbored the spirochaete.
The disease is readily transmitted to monkeys, rats, mice and other
animals and the earlier experiments along these lines have been
confirmed by many workers.
Not only are the ticks which have fed on infected individuals capable of
conveying the disease to healthy animals but they transmit the causative
organism to their progeny. Thus Mollers (1907), working in Berlin,
repeatedly infected monkeys through the bites of nymphs which had been
bred in the laboratory from infected ticks. Still more astonishing was
his discovery that ticks of the third generation were infective. In
other words, if the progeny of infected ticks were fed throughout life
on healthy animals, and on maturity deposited eggs, the nymphs which
hatched from these eggs would still be capable of carrying the
infection.
The developmental cycle of the spirochaete within the tick has not been
fully worked out, though the general conclusions of Leishman (1910) have
been supported by the recent works of Balfour (1911 and 1912), and
Hindle (1912), on the life cycle of spirochaetes affecting fowls.
_Spirochaeta duttoni_ ingested by _Ornithodoros moubata_ apparently
disappear within a few days, but Leishman believed that in reality they
break up into minute granules which are to be found in the alimentary
canal, the salivary glands and the Malpighian tubes of the tick. These
granules, or "coccoid bodies," as Hindle calls them, are supposed to be
the form in which the spirochaetes infect the new host. We shall see
later that Marchoux and Couvy (1913) dissent wholly from this
interpretation.
According to Leishman, and Hindle, the coccoid bodies are not injected
into the vertebrate host with the saliva of the tick, as are the
sporozoites of malaria with that of the mosquito. Instead, they pass out
with the excrement and secondarily gain access to the wound inflicted by
the tick.
Nuttall (1912) calls attention to the fact that the geographical
distribution of _Ornithodoros moubata_ is far wider than our present
records show for the distribution of the relapsing fever in man and that
there is every reason to fear the extension of the disease. Huts where
the ticks occur should be avoided and it should be remembered that in
infected localities there is special danger in sleeping on the ground.
EUROPEAN RELAPSING FEVER--There is widely distributed in Europe a type
of relapsing fever which is caused by _Spirochaeta recurrentis_. It has
long been supposed that this disease is spread by the bed-bug and there
is some experimental evidence to show that it may be conveyed by these
insects.
In 1897, Tictin found that he could infect monkeys by inoculating the
contents of bed-bugs which had fed upon a patient within forty-eight
hours. Nuttall, in 1907, in one experiment succeeded in transmitting
_Spirochaeta recurrentis_ from mouse to mouse by bites of bed-bugs. The
bugs, thirty-five in number, were transferred at short intervals from
one mouse to another, not being allowed to take a full meal on the
first, or infected mouse.
On the other hand, there is much clinical evidence to show that the
European relapsing fever like various other types of the disease is
transmitted from man to man by head and body lice (_Pediculus humanus_
and _Pediculus corporis_).
Interesting supplementary evidence is that of Bayon's observations
(1912), in Moscow. "Having visited the big municipal night hospitals at
Moscow I soon noticed that they were kept with such scrupulous
cleanliness, disinfected so lavishly, the beds of iron, the floor
cemented, that it was not possible for bed-bugs to thrive to any extent
on the premises. The people sleeping there were allowed, however, to
sleep in their own clothes. The introduction of these model homes had
not had any effect on the incidence of relapsing fever, for the places
were still hot-beds of the fever during winter. On the other hand,
though I changed my rooms several times, I found bugs in every
successive lodging, and I was told in Moscow, this can hardly be
avoided. Yet no foreigner, or Russian of the better class, ever catches
relapsing fever. To this may be added the fact that when I asked for
clothes-lice and promised to pay a kopec for two, the attendants from
the night hostel brought me next morning a small ounce bottle crammed
with _Pediculus capitis_ (= _P. humanus_), and _Pediculus vestimentorum_
(= _P. corporis_) collected off the sleepers. If relapsing fever were
transmitted by bed-bugs, it would be much more disseminated than it is
at present in Moscow."
Direct experimental evidence of the agency of lice in transmitting
relapsing fever is especially clear in the case of a type of the disease
prevalent in parts of North Africa. We shall consider this evidence
later.
OTHER TYPES OF RELAPSING FEVER OF MAN--In addition to the three types of
human relapsing fever already referred to, several others have been
distinguished and have been attributed to distinct species of
spirochaetes. The various spirochaetoses of man are:
African, caused by _S. duttoni_; European, caused by _S. recurrentis_;
North African, caused by _S. berbera_; East African, caused by _S.
rossi_; East Indian, caused by _S. carteri_; North American, caused by
_S. novyi_; South American, caused by _S. duttoni_ (?).
Nuttall (1912) in his valuable resume of the subject, has emphasized
that "in view of the morphological similarity of the supposedly
different species of spirochaetes and their individual variations in
virulence, we may well doubt if any of the 'species' are valid. As I
pointed out four years ago, the various specific names given to the
spirochaetes causing relapsing fever in man may be used merely for
convenience _to distinguish strains or races_ of different origin. They
cannot be regarded as valid names, in the sense of scientific
nomenclature, for virulence and immunity reactions are not adequate
tests of specificity."
NORTH AFRICAN RELAPSING FEVER OF MAN--The type of human relapsing fever
to be met with in Algeria, Tunis, and Tripoli, is due to a _Spirochaeta_
to which does not differ morphologically from _Spirochaeta duttoni_, but
which has been separated on biological grounds as _Spirochaeta berberi_.
Experimenting with this type of disease in Algeria, Sergent and Foly
(1910), twice succeeded in transmitting it from man to monkeys by
inoculation of crushed body lice and in two cases obtained infection of
human subjects who had received infected lice under their clothing and
who slept under coverings harboring many of the lice which had fed upon
a patient. Their results were negative with _Argas persicus_, _Cimex
lectularius_, _Musca domestica_, _Haematopinus spinulosus_ and
_Ceratophyllus fasciatus_. They found body lice associated with every
case of relapsing fever which they found in Algeria.
Nicolle, Blaizot, and Conseil (1912) showed that the louse did not
transmit the parasite by its bite. Two or three hours after it has fed
on a patient, the spirochaetes begin to break up and finally they
disappear, so that after a day, repeated examinations fail to reveal
them. They persist, nevertheless, in some unknown form, for if the
observations are continued they reappear in eight to twelve days. These
new forms are virulent, for a monkey was infected by inoculating a
single crushed louse which had fed on infected blood fifteen days
before.
Natural infection is indirect. Those attacked by the insect scratch, and
in this act they excoriate the skin, crush the lice and contaminate
their fingers. The least abrasion of the skin serves for the entrance of
the spirochaetes. Even the contact of the soiled fingers on the various
mucosa, such as the conjunctive of the eye, is sufficient.
As in the case of _Spirochaeta duttoni_, the organism is transmitted
hereditarily in the arthropod vector. The progeny of lice which have fed
on infected blood may themselves be infective.
SPIROCHAETOSIS OF FOWLS--One of the best known of the spirochaetes
transmitted by arthropods is _Spirochaeta gallinarum_, the cause of a
very fatal disease of domestic fowls in widely separated regions of the
world. According to Nuttall, it occurs in Southeastern Europe, Asia,
Africa, South America and Australia.
In 1903, Marchoux and Salimbeni, working in Brazil, made the first
detailed study of the disease, and showed that the causative organism is
transmitted from fowl to fowl by the tick _Argas persicus_. They found
that the ticks remained infective for at least five months. Specimens
which had fed upon diseased birds in Brazil were sent to Nuttall and he
promptly confirmed the experiments. Since that date many investigators,
notably Balfour and Hindle, have contributed to the elucidating of the
life-cycle of the parasite. Since it has been worked out more fully than
has that of any of the human spirochaetes, we present Hindle's diagram
(fig. 143) and quote the brief summary from his preliminary paper
(1911_b_).
"Commencing with the ordinary parasite in the blood of the fowl, the
spirochaete grows until it reaches a certain length (16-19u) and then
divides by transverse division. This process is repeated, and is
probably the only method of multiplication of the parasite within the
blood. When the spirochaetes disappear from the circulation, some of them
break up into the coccoid bodies which, however, do not usually develop
in the fowl. When the spirochaetes are ingested by _Argas persicus_, some
of them pass through the gut wall into the coelomic fluid. From this
medium they bore their way into the cells of the various organs of the
tick and there break up into a number of coccoid bodies. These
intracellular forms multiply by ordinary fission in the cells of the
Malpighian tubules and gonads. Some of the coccoid bodies are formed in
the lumen of the gut and Malpighian tubules. The result is that some of
the coccoid bodies may be present in the Malpighian secretion and
excrement of an infected tick and when mixed with the coxal fluid may
gain entry into another fowl by the open wound caused by the tick's
bite. They then elongate and redevelop into ordinary spirochaetes in the
blood of the fowl, and the cycle may be repeated."
[Illustration: 143. Spirochaeta gallinarum. After Hindle.]
Hindle's account is clear cut and circumstantial, and is quite in line
with the work of Balfour, and of Leishman. Radically different is the
interpretation of Marchoux and Couvy (1913). These investigators
maintain that the granules localized in the Malpighian tubules in the
larvae and, in the adult, also in the ovules and the genital ducts of the
male and female, are not derived from spirochaetes but that they exist
normally in many acariens. They interpret the supposed disassociation
of the spirochaete into granules as simply the first phase, not of a
process of multiplication, but of a degeneration ending in the death of
the parasite. The fragmented chromatin has lost its affinity for stains,
remaining always paler than that of the normal spirochaetes. On the other
hand, the granules of Leishman stain energetically with all the basic
stains.
Further, according to Marchoux and Couvy, infection takes place without
the emission of the coxal fluid and indeed, soiling of the host by the
coxal fluid diluting the excrement is exceptional. All of the organs of
the Argasid are invaded by the parasites, but they pass from the
coelom into the acini of the salivary glands and collect in its
efferent canal. The saliva serves as the vehicle of infection.
Thus, the question of the life cycle of _Spirochaeta gallinarum_, and of
spirochaetes in general, is an open one.
It should be noted that _Argas persicus_, the carrier of _Spirochaeta
gallinarum_, is a common pest of poultry in the southwestern United
States. Though the disease has not been reported from this country,
conditions are such that if accidentally introduced, it might do great
damage.
OTHER SPIROCHAETE DISEASES OF ANIMALS--About a score of other blood
inhabiting spirochaetes have been reported as occurring in mammals, but
little is known concerning their life-histories. One of the most
important is _Spirochaeta theileri_ which produces a spirochaetosis of
cattle in the Transvaal. Theiler has determined that it is transmitted
by an Ixodid tick, _Margaropus decoloratus_.
TYPHUS FEVER AND PEDICULIDAE
Typhus is an acute, and continued fever, formerly epidemically prevalent
in camps, hospitals, jails, and similar places where persons were
crowded together under insanitary conditions. It is accompanied by a
characteristic rash, which gives the disease the common name of
"spotted" or "lenticular" fever. The causative organism is unknown.
Typhus fever has not generally been supposed to occur in the United
States, but there have been a few outbreaks and sporadic cases
recognized. According to Anderson and Goldberger (1912_a_), it has been
a subject of speculation among health authorities why, in spite of the
arrival of occasional cases in this country and of many persons from
endemic foci of the disease, typhus fever apparently does not gain a
foothold in the United States. These same workers showed that the
so-called Brill's disease, studied especially in New York City, is
identical with the typhus fever of Mexico and of Europe.
The conditions under which the disease occurs and under which it spreads
most rapidly are such as to suggest that it is carried by some parasitic
insect. On epidemiological grounds the insects most open to suspicion
are the lice, bed-bugs and fleas.
In 1909, Nicolle, Comte and Conseil, succeeded in transmitting typhus
fever from infected to healthy monkeys by means of the body louse
(_Pediculus corporis_). Independently of this work, Anderson and
Goldberger had undertaken work along this line in Mexico, and in 1910
reported two attempts to transmit the disease to monkeys by means of
body lice. The first experiment resulted negatively, but the second
resulted in a slight rise in temperature, and in view of later results
it seems that this was due to infection with typhus.
Shortly after, Ricketts and Wilder (1910) succeeded in transmitting the
disease to the monkey by the bite of body lice in two experiments, the
lice in one instance deriving their infection from a man and in another
from the monkey. Another monkey was infected by typhus through the
introduction of the feces and abdominal contents of infested lice into
small incisions. Experiments with fleas and bed-bugs resulted
negatively.
Subsequently, Goldberger and Anderson (1912_b_) indicated that the head
louse (_Pediculus humanus_) as well, may become infected with typhus. In
an attempt to transmit typhus fever (Mexican virus) from man to monkey
by subcutaneous injection of a saline suspension of crushed head lice,
the monkeys developed a typical febrile reaction with subsequent
resistance to an inoculation of virulent typhus (Mexican) blood. In one
of the three experiments to transmit the disease from man to monkey by
means of the bite of the head louse, the animal bitten by the presumably
infected head lice proved resistant to two successive immunity tests
with virulent typhus blood.
In 1910, Ricketts and Wilder reported an experiment undertaken with a
view to determining whether the young of infected lice were themselves
infected. Young lice were reared to maturity on the bodies of typhus
patients, so that if the eggs were susceptible to infection at any stage
of their development, they would have every opportunity of being
infected within the ovary. The eggs of these infected lice were
obtained, they were incubated, and the young lice of the second
generation were placed on a normal rhesus monkey. The experimenters were
unable to keep the monkey under very close observation during the
following three or four weeks, but from the fact that he proved
resistant to a subsequent immunity test they concluded that he probably
owed this immunity to infection by these lice of the second generation.
Anderson and Goldberger (1912_b_) object that due consideration was not
given to the possibility of a variable susceptibility of the monkey to
typhus. Their similar experiment was "frankly negative."
Prophylaxis against typhus fever is, therefore, primarily a question of
vermin extermination. A brief article by Dr. Goldberger (1914) so
clearly shows the practical application of his work and that of the
other investigators of the subject, that we abstract from it the
following account:
"In general terms it may be stated that association with a case of
typhus fever in the absence of the transmitting insect is no more
dangerous than is association with a case of yellow fever in the absence
of the yellow fever mosquito. Danger threatens only when the insect
appears on the scene."
"We may say, therefore, that to prevent infection of the individual it
is necessary for him only to avoid being bitten by the louse. In theory
this may readily be done, for we know that the body louse infests and
attaches itself almost entirely to the body linen, and that boiling
kills this insect and its eggs. Individual prophylaxis is based
essentially, therefore, on the avoidance of contact with individuals
likely to harbor lice. Practically, however, this is not always as easy
as it may seem, especially under the conditions of such intimate
association as is imposed by urban life. Particularly is this the case
in places such as some of the large Mexican cities, where a large
proportion of the population harbors this vermin. Under such
circumstances it is well to avoid crowds or crowded places, such as
public markets, crowded streets, or public assemblies at which the
'peon' gathers."
"Community prophylaxis efficiently and intelligently carried out is,
from a certain point of view, probably easier and more effective in
protecting the individual than is the individual's own effort to guard
himself. Typhus emphasizes, perhaps better than any other disease, the
fact that fundamentally, sanitation and health are economic problems. In
proportion as the economic condition of the masses has improved--that
is, in proportion as they could afford to keep clean--the notorious
filth disease has decreased or disappeared. In localities where it still
prevails, its further reduction or complete eradication waits on a
further improvement in, or extension of, the improved economic status of
those afflicted. Economic evolution is very slow process, and, while
doing what we can to hasten it, we must take such precautions as
existing conditions permit, looking to a reduction in or complete
eradication of the disease."
"When possible, public bath houses and public wash houses, where the
poor may bathe and do their washings at a minimum or without cost,
should be provided. Similar provision should be made in military and
construction camps. Troops in the field should be given the opportunity
as frequently as possible to wash and _scald_ or _boil_ their body
linen."
"Lodging houses, cheap boarding houses, night shelters, hospitals, jails
and prisons, are important factors in the spread and frequently
constitute foci of the disease. They should receive rigid sanitary
supervision, including the enforcement of measures to free all inmates
of such institutions of lice on admission."
"So far as individual foci of the disease are concerned these should be
dealt with by segregating and keeping under observation all exposed
individuals for 14 days--the period of incubation--from the last
exposure, by disinfecting (boiling or steaming) the suspected bedding,
body linen, and clothes, for the destruction of any possible vermin that
they may harbor, and by fumigating (with sulphur) the quarters that they
may have occupied."
"It will be noted that nothing has been said as to the disposition of
the patient. So far as the patient is concerned, he should be removed to
'clean' surroundings, making sure that he does not take with him any
vermin. This may be done by bathing, treating the hair with an
insecticide (coal oil, tincture of larkspur), and a complete change of
body linen. Aside from this, the patient may be treated or cared for in
a general hospital ward or in a private house, provided the sanitary
officer is satisfied that the new surroundings to which the patient has
been removed are 'clean,' that is, free from vermin. Indeed, it is
reasonably safe to permit a 'clean' patient to remain in his own home if
this is 'clean,' for, as has already been emphasized, there can be no
spread in the absence of lice. This is a common experience in native
families of the better class and of Europeans in Mexico City."
"Similarly the sulphur fumigation above prescribed may be dispensed with
as unnecessary in this class of cases."
CHAPTER XI
SOME POSSIBLE, BUT IMPERFECTLY ESTABLISHED CASES OF ARTHROPOD
TRANSMISSION OF DISEASE
INFANTILE PARALYSIS OR ACUTE ANTERIOR POLIOMYELITIS
The disease usually known in this country as infantile paralysis or,
more technically, as acute anterior poliomyelitis, is one which has
aroused much attention in recent years.
The causative organism of infantile paralysis is unknown, but it has
been demonstrated that it belongs to the group of filterable viruses. It
gives rise to a general infection, producing characteristic lesions in
the central nervous system. The result of the injury to the motor nerves
is a more or less complete paralysis of the corresponding muscle. This
usually manifests itself in the legs and arms. The fatal cases are
usually the result of paralysis of the muscles of respiration. Of the
non-fatal cases about 60 per cent remain permanently crippled in varying
degrees.
Though long known, it was not until about 1890 that it was emphasized
that the disease occurs in epidemic form. At this time Medin reported
his observations on an epidemic of forty-three cases which occurred in
and around Stockholm in 1887. Since then, according to Frost (1911),
epidemics have been observed with increasing frequency in various parts
of the world. The largest recorded epidemics have been those in Vermont,
1894, 126 cases; Norway and Sweden, 1905, about 1,500 cases; New York
City, 1907, about 2,500 cases. Since 1907 many epidemics have been
reported in the United States, and especially in the Northern States
east of the Dakotas. In 1912 there were over 300 cases of the disease in
Buffalo, N. Y., with a mortality of somewhat over 11 per cent.
In view of the sudden prominence and the alarming spread of infantile
paralysis, there have been many attempts to determine the cause, and the
manner in which the disease spreads and develops in epidemic form. In
the course of these studies, the question of possible transmission by
insects was naturally suggested.
C. W. Howard and Clark (1912) presented the results of studies in this
phase of the subject. They dealt especially with the house-fly, bedbug,
head, and body lice, and mosquitoes. It was found that the house-fly
(_Musca domestica_) can carry the virus of poliomyelitis in an active
state for several days upon the surface of the body and for several
hours within the gastro-intestinal tract. Mosquitoes and lice were found
not to take up or maintain the virus. On the other hand, the bedbug
(_Cimex lectularius_) was found to take the virus from the infected
monkeys and to maintain it in a living state within the body for a
period of seven days. This was demonstrated by grinding up in salt
solution, insects which had fed on poliomyelitic animals and injecting
the filtrate into a healthy monkey. The experimenters doubted that the
bedbug is a carrier of the virus in nature.
Earlier in the same year, Brues and Sheppard published the results of an
intensive epidemiological study of the outbreak of 1911, in
Massachusetts. Special attention had been paid to the possibility of
insect transfer and the following conclusion was reached:
"Field work during the past summer together with a consideration of the
epidemiology of the disease so far as known, points strongly toward
biting flies as possible carriers of the virus. It seems probable that
the common stable-fly (_Stomoxys calcitrans_ L.) may be responsible to a
certain extent for the spread of acute epidemic poliomyelitis, possibly
aided by other biting flies, such as _Tabanus lineola_. No facts which
disprove such a hypothesis have as yet been adduced, and experiments
based upon it are now in progress."
As stated by Brues (1913), especial suspicion fell upon the stable-fly
because:
1. The blood-sucking habits of the adult fly suit it for the transfer of
virus present in the blood.
2. The seasonal abundance of the fly is very closely correlated with the
incidence of the disease, rising rapidly during the summer and reaching
a maximum in July and August, then slowly declining in September and
October.
3. The geographical distribution of the fly is, so far as can be
ascertained, wider, or at least co-extensive with that of poliomyelitis.
4. _Stomoxys_ is distinctly more abundant under rural conditions, than
in cities and thickly populated areas.
5. While the disease spreads over districts quickly and in a rather
erratic way, it often appears to follow along lines of travel, and it is
known that _Stomoxys_ flies will often follow horses for long distances
along highways.
6. In a surprisingly large number of cases, it appeared probable that
the children affected had been in the habit of frequenting places where
_Stomoxys_ is particularly abundant, i.e., about stables, barnyards,
etc.
The experiments referred to were carried on during the summer of 1912
and in September Dr. Rosenau announced that the disease was transferred
by the bite of the stable-fly.
A monkey infected by inoculation was exposed to the bites of upwards of
a thousand of the _Stomoxys_ flies daily, by stretching it at full
length and rolling it in a piece of chicken wire, and then placing it on
the floor of the cage in which the flies were confined. The flies fed
freely from the first, as well as later, after paralysis had set in.
Alternating with the inoculated monkey, healthy monkeys were similarly
introduced into the cage at intervals. New monkeys were inoculated to
keep a supply of such infected animals and additional healthy ones were
exposed to the flies, which fed willingly and in considerable numbers on
each occasion. "Thus the flies were given every opportunity to obtain
infection from the monkeys, since the animals were bitten during
practically every stage of the disease from the time of the inoculation
of the virus till their death following the appearance of paralysis. By
the same arrangement the healthy monkeys were likely to be bitten by
flies that had previously fed during the various stages of the disease
on the infected monkeys. The flies had meanwhile enjoyed the opportunity
of incubating the virus for periods varying from the day or two which
usually elapses between consecutive feedings, to the two or three-week
period for which at least some (although a very small percentage) of the
flies lived in the cage."
"In all, twelve apparently healthy monkeys of a small Japan species were
exposed to the flies in the manner described for the infected monkeys.
Some were placed in the cage only once or twice and others a number of
times after varying intervals. These exposures usually lasted for about
half an hour, but were sometimes more protracted. No results were
apparent until two or three weeks after the experiment was well under
way, and then in rather rapid succession six of the animals developed
symptoms of poliomyelitis. In three, the disease appeared in a virulent
form, resulting in death, while the other three experienced transient
tremblings, diarrhoea, partial paralysis and recovery."--Brues, 1913.
Very soon after the announcement of the results of experiments by
Rosenau and Brues, they were apparently conclusively confirmed by
Anderson and Frost (1912), who repeated the experiments, at Washington.
They announced that through the bites of the _Stomoxys_ flies that had
previously fed on infected monkeys, they had succeeded in experimentally
infecting three healthy monkeys.
The results of these experiments gained much publicity and in spite of
the conservative manner in which they had been announced, it was widely
proclaimed that infantile paralysis was conveyed in nature by the
stable-fly and by it alone.
Serious doubt was cast on this theory by the results of further
experiments by Anderson and Frost, reported in May of 1913. Contrary to
the expectations justified by their first experience, the results of all
the later, and more extended, experiments were wholly negative. Not once
were these investigators again able to transmit the infection of
poliomyelitis through _Stomoxys_. They concluded that it was extremely
doubtful that the insect was an important factor in the natural
transmission of the disease, not only because of their series of
negative results, "but also because recent experiments have afforded
additional evidence of the direct transmissibility or contagiousness of
poliomyelitis, and because epidemiological studies appear to us to
indicate that the disease is more likely transmitted largely through
passive human virus carriers."
Soon after this, Kling and Levaditi (1913) published their detailed
studies on acute anterior poliomyelitis. They considered that the
experiments of Flexner and Clark (and Howard and Clark), who fed
house-flies on emulsion of infected spinal cord, were under conditions
so different from what could occur in nature that one could not draw
precise conclusions from them regarding the epidemiology of the disease.
They cited the experiments of Josefson (1912), as being under more
reasonable conditions. He sought to determine whether the inoculation of
monkeys with flies caught in the wards of the Hospital for Contagious
Diseases at Stockholm, where they had been in contact with cases of
poliomyelitis, would produce the disease. The results were completely
negative.
Kling and Lavaditi made four attempts of this kind. The flies were
collected in places where poliomyelitics had dwelt, three, four and
twenty-four after the beginning of the disease in the family and one,
three, and fifteen days after the patient had left the house. These
insects were for the greater part living and had certainly been in
contact with the infected person. In addition, flies were used which had
been caught in the wards of the Hospital for Contagious Diseases at
Soderkoping, when numbers of poliomyelitics were confined there.
Finally, to make the conditions as favorable as possible, the emulsions
prepared from these flies were injected without previous filtering,
since filtration often causes a weakening of the virus. In spite of
these precautions, all their results were negative, none of the
inoculated animals having contracted poliomyelitis. They also
experimented with bedbugs which had fed upon infected patients at
various stages of the disease, but the results in these cases also were
wholly negative.
Kling and Levaditi considered at length the possibility of transmission
of the disease by _Stomoxys_. As a result of their epidemiological
studies, they found that infantile paralysis continued to spread in
epidemic form in the dead of winter, when these flies were very rare and
torpid, or were even completely absent. Numerous cases developed in the
northern part of Sweden late in October and November, long after snow
had fallen. On account of the rarity of the Stomoxys flies during the
period of their investigations they were unable to conduct satisfactory
experiments. In one instance, during a severe epidemic, they found a
number of the flies in a stable near a house inhabited by an infected
family, though none was found in the house itself. These flies were used
in preparing an emulsion which, after filtering, was injected into the
peritoneal cavity of a monkey. The result was wholly negative.
As for the earlier experiments, Kling and Levaditi believe if the flies
were responsible for the transmission of the disease in the cases
reported by Rosenau and Brues, and the first experiments of Anderson and
Frost, it was because the virus of infantile paralysis is eliminated
with the nasal secretions of paralyzed monkeys and the flies, becoming
contaminated, had merely acted as accidental carriers.
Still further evidence against the hypothesis of the transmission of
acute anterior poliomyelitis by _Stomoxys calcitrans_ was brought
forward by Sawyer and Herms (1913). Special precautions were used to
prevent the transference of saliva or other possibly infectious material
from the surface of one monkey to that of another, and to avoid the
possibility of complicating the experiments by introducing other
pathogenic organisms from wild flies, only laboratory-bred flies were
used. In a series of seven carefully performed experiments, in which the
conditions were varied, Sawyer and Herms were unable to transmit
poliomyelitis from monkey to monkey through the agency of _Stomoxys_, or
to obtain any indication that the fly is the usual agent for spreading
the disease in nature.
The evidence at hand to date indicates that acute anterior
poliomyelitis, or infantile paralysis, is transmitted by contact with
infected persons. Under certain conditions insects may be agents in
spreading the disease, but their role is a subordinate one.
Pellagra
PELLAGRA is an endemic and epidemic disease characterized by a peculiar
eruption or erythema of the skin (figs 144 and 145), digestive
disturbances and nervous trouble. Insanity is a common result, rather
than a precursor of the disease. The manifestations of pellagra are
periodic and its duration indeterminate.
[Illustration: 144. Pellagrous eruption on the face. After Watson.]
The disease is one the very name of which was almost unknown in the
United States until within the past decade. It has usually been regarded
as tropical, though it occurs commonly in Italy and in various parts of
Europe. Now it is known that it not only occurs quite generally in the
United States but that it is spreading. Lavinder (1911) says that "There
are certainly many thousand cases of the disease in this country, and
the present situation must be looked upon with grave concern."
It is not within the scope of this book to undertake a general
discussion of pellagra. The subject is of such importance to every
medical man that we cannot do better than refer to Lavinder's valuable
precis. We can only touch briefly upon the entomological phases of the
problems presented.
The most commonly accepted theories regarding the etiology of the
disease have attributed it to the use of Indian corn as an article of
diet. This supposed relationship was explained either on the basis of,
(a) insufficiency of nutriment and inappropriateness of corn as a prime
article of food; (b) toxicity of corn or, (c) parasitism of certain
organisms--fungi or bacteria--ingested with either sound or deteriorated
corn.
In 1905, Sambon proposed the theory of the protozoal origin of pellagra
and in 1910 he marshalled an imposing array of objections to the theory
that there existed any relationship between corn and the disease. He
presented clear evidence that pellagra existed in Europe before the
introduction of Indian corn from America, as an article of diet, and
that its spread was not _pari passu_ with that of the use of corn. Cases
were found in which the patients had apparently never used corn, though
that is obviously difficult to establish. He showed that preventive
measures based on the theory had been a failure. Finally, he believed
that the recurrence of symptoms of the disease for successive springs,
in patients who abstained absolutely from the use of corn, militated
against the theory.
[Illustration: 145. Pellagrous eruption on the hand. After Watson.]
On the other hand, Sambon believed that the periodicity of the symptoms,
peculiarities of distribution and seasonal incidence, and analogies of
the symptoms to those of other parasitic diseases indicated that
pellagra was of protozoal origin, and that it was insect-borne.
The insect carriers, he believed to be one or more species of Simuliidae,
or black-flies. In support of this he stated that _Simulium_ appears to
effect the same topographical conditions as pellagra, that in its imago
stage it seems to present the same seasonal incidence, that it has a
wide geographical distribution which seems to cover that of pellagra,
and that species of the genus are known to cause severe epizootics.
Concluding from his studies in Italy, that pellagra was limited almost
wholly to agricultural laborers, he pointed out that the Simulium flies
are found only in rural districts, and as a rule do not enter towns,
villages, or houses.
[Illustration: 146. A favorite breeding place of Simulium. Ithaca, N.
Y.]
When Sambon's detailed report was published in 1910, his theory was
seized upon everywhere by workers who were anxious to test it and who,
in most cases, were favorably disposed towards it because of the
wonderful progress which had been made in the understanding of other
insect-borne diseases. In this country, the entomological aspects of the
subject have been dealt with especially by Forbes (1912), and by King
and Jennings, under the direction of W. D. Hunter, of the Bureau of
Entomology, and in cooperation with the Thompson-McFadden Pellagra
Commission of the Department of Tropical Medicine of the New York
Post-Graduate Medical School. An important series of experiments with
monkeys has been undertaken by S. J. Hunter, of Kansas, but
unfortunately we have as yet no satisfactory evidence that these animals
are susceptible to the disease--a fact which renders the whole problem
difficult.
The accumulated evidence is increasingly opposed to Sambon's hypothesis
of the transmission of pellagra by _Simulium_. This has been so clearly
manifested in the work of the Thompson-McFadden Commission that we quote
here from the report by Jennings (1914):
"Our studies in 1912 convinced us that there was little evidence to
support the incrimination of any species of _Simulium_ in South Carolina
in the transmission of pellagra. Reviewing the group as a whole, we find
that its species are essentially "wild" and lack those habits of
intimate association with man which would be expected in the vector of
such a disease as pellagra. Although these flies are excessively
abundant in some parts of their range and are moderately so in
Spartanburg County, man is merely an incidental host, and no disposition
whatever to seek him out or to invade his domicile seems to be
manifested. Critically considered, it is nearer the fact that usually
man is attacked only when he invades their habitat."
"As our knowledge of pellagra accumulates, it is more and more evident
that its origin is in some way closely associated with the domicile. The
possibility that an insect whose association with man and his immediate
environment is, at the best, casual and desultory, can be active in the
causation of the disease becomes increasingly remote."
"Our knowledge of the biting habits of _Simulium_ is not complete, but
it is evident, as regards American species at least, that these are
sometimes not constant for the same species in different localities.
Certain species will bite man freely when opportunity offers, while
others have never been known to attack him. To assume that the proximity
of a _Simulium_-breeding stream necessarily implies that persons in its
vicinity must be attacked and bitten is highly fallacious. In
Spartanburg County attacks by _Simulium_ seems to be confined to the
immediate vicinity of the breeding-places. Our records and observations,
exceedingly few in number, refer almost exclusively to such locations.
Statements regarding such attacks, secured with much care and
discrimination from a large number of persons, including many
pellagrins, indicate conclusively that these insects are seldom a pest
of man in this county. A certain number of the persons questioned were
familiar with the gnats in other localities, but the majority were
seemingly ignorant of the existence of such flies with biting habits.
This is especially striking, in view of the fact that the average
distance of streams from the homes of the pellagra cases studied was
about 200 yards, many being at a distance of less than 200 yards, and
that 78 per cent of these streams were found to be infested by larval
_Simulium_. Such ignorance in a large number of persons cannot be
overlooked and indicates strongly that our belief in the negligible
character of local attacks by _Simulium_ is well founded."
"In localities infested by 'sand-flies,' mosquitoes, etc., these pests
are always well known and the ignorance described above is very
significant."
"Such positive reports as we received nearly always referred to bites
received in the open, along streams, etc., and observations made of
their attack were of those on field laborers in similar situations.
Males engaged in agricultural pursuits are almost exempt from pellagra
in Spartanburg County. During the season of 1913, in some two or three
instances, observations were made of the biting of _Simulium_ and some
additional and entirely creditable reports were received. These
observations and reports were under conditions identical with those
referred to in the reports of 1912 and confirm the conclusions based on
the observations of that year. I would repeat with emphasis that it is
inconceivable that a fly of the appearance and habits of the prevalent
species of _Simulium_ could be present in such a region, especially
about the haunts of man and attack him with sufficient frequency and
regularity to satisfactorily account for so active and prevalent a
disease as pellagra without being a well-known and recognized pest."
"In connection with the conditions in the Piedmont region of South
Carolina, it may be well to cite the results of a study of those in the
arid region of western Texas."
"In May, 1913, in company with Capt. J. F. Siler of the
Thompson-McFadden Pellagra Commission, I visited the region of which
Midland in Midland County is the center. This region is very dry and
totally devoid of running water for a long distance in every direction.
The only natural source of water-supply, a few water holes and ponds,
were visited and found to be of such a nature that the survival of
_Simulium_, far less its propagation in them, is absolutely impossible.
The nearest stream affording possibilities as a source of _Simulium_ is
60 miles away, while the average distance of such possibility is not
less than 100 miles."
"Artificial sources of water-supply were also investigated carefully and
were found to offer no opportunity for the breeding of _Simulium_."
"At Midland the histories of five cases of pellagra were obtained, which
gave clear evidence that this place or its immediate vicinity was the
point of origin. Persons of long residence in the country were
questioned as to the occurrence of such flies as _Simulium_ and returned
negative answers. These included a retired cattle owner, who is a man of
education and a keen observer, an expert veterinarian stationed in the
country who has the cattle of the country under constant observation,
and a practical cattle man, manager of a ranch and of wide experience.
The latter had had experience with 'Buffalo gnats' in other localities
(in the East) and is well acquainted with them. His close personal
supervision of the cattle under his charge, makes it practically certain
that he would have discovered these gnats had they been present in the
country."
"At the time the study was made, _Simulium_ was breeding and active in
the adult state in the vicinity of Dallas, Texas, in the eastern part of
the state. We have here a region in which cases of pellagra have
originated, yet in which _Simulium_ does not and cannot breed."
Other possible insect vectors of pellagra have been studied in great
detail and the available evidence indicates that if _any_ insect plays a
role in the spread of the disease, _Stomoxys calcitrans_ most nearly
fills the conditions. This conclusion was announced by Jennings and King
in 1912, and has been supported by their subsequent work.
Yet, after all the studies of the past decade, the old belief that
pellagra is essentially of dietary origin is gaining ground. Goldberger,
Waring and Willets (1914) of the United States Public Health Service
summarize their conclusions in the statement, (1) that it is dependent
on some yet undetermined fault in a diet in which the animal or
leguminous protein component is disproportionately large and (2) that no
pellagra develops in those who _consume_ a mixed, well-balanced, and
varied diet, such, for example, as that furnished by the Government to
the enlisted men of the Army, Navy, and Marine Corps.
Leprosy
LEPROSY is a specific, infectious disease due to _Bacillus leprae_, and
characterized by the formation of tubercular nodules, ulcerations, and
disturbances of sensation. In spite of the long time that the disease
has been known and the dread with which it is regarded, little is known
concerning the method of transfer of the causative organism or the means
by which it gains access to the human body.
It is known that the bacilli are to be found in the tubercles, the scurf
of the skin, nasal secretions, the sputum and, in fact in practically
all the discharges of the leper. Under such conditions it is quite
conceivable that they may be transferred in some instances from diseased
to healthy individuals through the agency of insects and other
arthropods. Many attempts have been made to demonstrate this method of
spread of the disease, but with little success.
Of the suggested insect carriers none seem to meet the conditions better
than mosquitoes, and there are many suggestions in literature that these
insects play an important role in the transmission of leprosy. The
literature has been reviewed and important experimental evidence
presented by Currie (1910). He found that mosquitoes feeding, under
natural conditions, upon cases of nodular leprosy so rarely, if ever,
imbibe the lepra bacillus that they cannot be regarded as one of the
ordinary means of transference of this bacillus from lepers to the skin
of healthy persons. He believes that the reason that mosquitoes that
have fed on lepers do not contain the lepra bacillus is that when these
insects feed they insert their proboscis directly into a blood vessel
and thus obtain bacilli-free blood, unmixed with lymph.
The same worker undertook to determine whether flies are able to
transmit leprosy. He experimented with five species found in
Honolulu,--_Musca domestica_, _Sarcophaga pallinervis_, _Sarcophaga
barbata_, _Volucella obesa_ and an undetermined species of _Lucilia_.
The experiments with _Musca domestica_ were the most detailed. From
these experiments he concluded, first, that all of the above-named
flies, when given an opportunity to feed upon leprous fluids, will
contain the bacilli in their intestinal tracts and feces for several
days after such feeding. Second, that considering the habits of these
flies, and especially those of _Musca domestica_, it is certain that,
given an exposed leprous ulcer, these insects will frequently convey
immense numbers of lepra bacilli, directly or indirectly, to the skins,
nasal mucosa, and digestive tracts of healthy persons. Additional
evidence along this line has recently been brought forward by Honeij and
Parker (1914), who incriminate both _Musca domestica_ and _Stomoxys
calcitrans_. Whether or not such insect-borne bacilli are capable of
infecting persons whose skin and mucosa are thus contaminated, Currie
was unwilling to maintain, but he concludes that until we have more
accurate knowledge on this point, we are justified in regarding these
insects with grave suspicion of being one of the means of disseminating
leprous infection.
Various students of the subject have suggested that bed-bugs may be the
carriers of leprosy and have determined the presence of acid-fast
bacilli in the intestines of bed-bugs which had fed on leprous patients.
Opposed to this, the careful experiments of Thompson (1913) and of
Skelton and Parkham (1913) have been wholly negative.
Borrel has recently suggested that _Demodex_, may play a role in
spreading the infection in families. Many other insects and acariens
have been suggested as possible vectors, but the experimental data are
few and in no wise conclusive. The most that can be said is that it is
quite possible that under favorable conditions the infection might be
spread by any of the several blood-sucking forms or by house-flies.
Verruga peruviana
VERRUGA PERUVIANA is defined by Castellani and Chalmers as "a chronic,
endemic, specific, general disorder of unknown origin, not contagious,
but apparently inoculable, and characterized by an irregular fever
associated with rheumatoid pains, anemia, followed by granulomatous
swellings in the skin, mucous membranes, and organs of the body." It has
been generally believed by medical men interested that the comparatively
benign eruptive verruga is identical with the so-called Oroya, or
Carrion's fever, a malignant type. This view is not supported by the
work of Strong, Tyzzer and Brues, (1913).
The disease is confined to South America and to definitely limited areas
of those countries in which it does occur. It is especially prevalent in
some parts of Peru.
The causative organism and the method of transfer of verruga are
unknown. Castellani and Chalmers pointed out in 1910 that the study of
the distribution of the disease in Peru would impress one with the
similarity to the distribution of the Rocky Mountain fever and would
lead to the conclusion that the aetiological cause must in some way be
associated with some blood-sucking animal, perhaps an arachnid, and that
this is supported by the fact that the persons most prone to the
infection are those who work in the fields.
More recently, Townsend (1913), in a series of papers, has maintained
that verruga and Carrion's disease are identical, and that they are
transmitted to man by the bites of the Psychodid fly, _Phlebotomus
verrucarum_. He succeeded in producing the eruptive type of the disease
in experimental animals by injecting a physiological salt trituration of
wild Phlebotomus flies. A cebus monkey was exposed from October so to
November 6, by chaining him to a tree in the verruga zone, next to a
stone wall from which the flies emerged in large numbers every night.
Miliar eruption began to appear on the orbits November 13 and by
November 21, there were a number of typical eruptions, with exudation on
various parts of the body exactly like miliar eruptive sores commonly
seen on legs of human cases.
An assistant in the verruga work, George E. Nicholson, contracted the
eruptive type of the disease, apparently as a result of being bitten by
the Phlebotomus flies. He had slept in a verruga zone, under a tight
net. During the night he evidently put his hands in contact with the
net, for in the morning there were fifty-five unmistakable Phlebotomus
bites on the backs of his hands and wrists.
Townsend believes that in nature, lizards constitute the reservoir of
the disease and that it is from them that the Phlebotomus flies receive
the infection.
Cancer
There are not wanting suggestions that this dread disease is carried, or
even caused, by arthropods. Borrel (1909) stated that he had found mites
of the genus _Demodex_ in carcinoma of the face and of the mammae. He
believed that they acted as carriers of the virus.
Saul (1910) and Dahl (1910) go much further, since they attribute the
production of the malignant growth to the presence of mites which Saul
had found in cancers. These Dahl described as belonging to a new
species, which he designated _Tarsonemus hominis_. These findings have
since been confirmed by several workers. Nevertheless, the presence of
the mite is so rare that it cannot be regarded as an important factor in
the causation of the disease. The theory that cancer is caused by an
external parasite is given little credence by investigators in this
field.
IN CONCLUSION, it should be noted that the medical and entomological
literature of the past few years abounds in suggestions, and in
unsupported direct statements that various other diseases are
insect-borne. Knab (1912) has well said "Since the discovery that
certain blood-sucking insects are the secondary hosts of pathogenic
parasites, nearly every insect that sucks blood, whether habitually or
occasionally, has been suspected or considered a possible transmitter of
disease. No thought seems to have been given to the conditions and the
characteristics of the individual species of blood-sucking insects,
which make disease transmission possible."
He points out that "in order to be a potential transmitter of human
blood-parasites, an insect must be closely associated with man and
normally have opportunity to suck his blood repeatedly. It is not
sufficient that occasional specimens bite man, as, for example, is the
case with forest mosquitoes. Although a person may be bitten by a large
number of such mosquitoes, the chances that any of these mosquitoes
survive to develop the parasites in question, (assuming such development
to be possible), and then find opportunity to bite and infect another
person, are altogether too remote. Applying this criterion, not only the
majority of mosquitoes but many other blood-sucking insects, such as
Tabanidae and Simuliidae, may be confidently eliminated. Moreover,
these insects are mostly in evidence only during a brief season, so that
we have an additional difficulty of a very long interval during which
there could be no propagation of the disease in question." He makes an
exception of tick-borne diseases, where the parasites are directly
transmitted from the tick host to its offspring and where, for this
reason, the insect remains a potential transmitter for a very long
period. He also cites the trypanosome diseases as possible exceptions,
since the causative organisms apparently thrive in a number of different
vertebrate hosts and may be transmitted from cattle, or wild animals, to
man.
Knab's article should serve a valuable end in checking irresponsible
theorizing on the subject of insect transmission of disease.
Nevertheless, the principles which he laid down cannot be applied to the
cases of accidental carriage of bacterial diseases, or to those of
direct inoculation of pyogenic organisms, or of blood parasites such as
the bacillus of anthrax, or of bubonic plague. Accumulated evidence has
justified the conclusion that certain trypanosomes pathogenic to man are
harbored by wild mammals, and so form an exception. Townsend believes
that lizards constitute the natural reservoir of verruga; and it seems
probable that field mice harbor the organism of tsutsugamushi disease.
Such instances are likely to accumulate as our knowledge of the relation
of arthropods to disease broadens.
CHAPTER XII
HOMINOXIOUS ARTHROPODS
The following synoptic tables are presented in the hope that they may be
of service in giving the reader a perspective of the relationships of
the Arthropoda in general and enabling him to identify the more
important species which have been found noxious to man. Though
applicable chiefly to the arthropods found in the United States, exotic
genera and species which are concerned in the transmission of disease
are also included. For this reason the keys to the genera of the Muscids
of the world are given. As will be seen, the tables embrace a number of
groups of species which are not injurious. This was found necessary in
order that the student might not be lead to an erroneous determination
which would result were he to attempt to identify a species which
heretofore had not been considered noxious, by means of a key containing
only the noxious forms. The names printed in BOLD FACED TYPE indicate
the hominoxious arthropods which have been most commonly mentioned in
literature.
CRUSTACEA
Arthropods having two pairs of antennae which are sometimes modified for
grasping, and usually with more than five pairs of legs. With but few
exceptions they are aquatic creatures. Representatives are: Crabs,
lobsters, shrimps, crayfish, water-fleas, and woodlice. To this class
belongs the CYCLOPS (fig. 122) a genus of minute aquatic crustaceans of
which at least one species harbors _Dracunculus medinensis_, the Guinea
worm (fig. 121).
MYRIAPODA
Elongate, usually vermiform, wingless, terrestrial creatures having one
pair of antennae, legs attached to each of the many intermediate body
segments. This group is divided into two sections, now usually given
class rank: the DIPLOPODA or millipedes (fig. 13), commonly known as
thousand legs, characterized by having two pairs of legs attached to
each intermediate body segment, and the CHILOPODA or centipedes (fig.
14) having only one pair of legs to each body segment.
ARACHNIDA
In this class the antennae are apparently wanting, wings are never
present, and the adults are usually provided with four pairs of legs.
Scorpions, harvest-men, spiders, mites, etc.
HEXAPODA (Insects)
True insects have a single pair of antennae, which is rarely vestigial,
and usually one or two pairs of wings in the adult stage. Familiar
examples are cockroaches, crickets, grasshoppers, bugs, dragon-flies,
butterflies, moths, mosquitoes, flies, beetles, ants, bees and wasps.
ORDERS OF THE ARACHNIDA
a. Abdomen distinctly segmented. A group of orders including scorpions,
(fig. 11), whip-scorpions (fig. 10), pseudo-scorpions, solpugids
(fig. 12) harvest-men (daddy-long-legs or harvestmen), etc.
ARTHROGASTRA
aa. Abdomen unsegmented, though sometimes with numerous annulations
SPHAEROGASTRA
b. A constriction between cephalothorax and abdomen (fig. 7). True
Spiders ARANEIDA
bb. No deep constriction between these parts.
c. Legs usually well developed, body more or less depressed (fig.
49). Mites ACARINA
cc. Legs stumpy or absent, body more or less elongate or vermiform,
or if shorter, the species is aquatic or semi-aquatic in habit.
d. Four pairs of short legs; species inhabiting moss or water.
Water-bears. TARDIGRADA
dd. Two pairs of clasping organs near the mouth, instead of legs,
in the adult; worm-like creatures parasitic within the nasal
passages, lungs, etc. of mammals and reptiles (fig. 148).
Tongue worms. LINGUATULINA
[Illustration: 148. Linguatula. (_a_) larva; (enlarged). (_b_) adult;
(natural size).]
ACARINA[E]
a. Abdomen annulate, elongate; very minute forms, often with but four
legs (fig. 62). DEMODICOIDEA
b. With but four legs of five segments each. Living on plants, often
forming galls. ERIOPHYIDAE
bb. With eight legs, of three segments each. Living in the skin of
mammals. DEMODICIDAE
To this family belongs the genus DEMODEX found in the sebaceous
glands and hair follicles of various mammals, including man. _D.
phylloides_ Csokor has been found in Canada on swine, causing
white tubercles on the skin. _D. bovis_ Stiles has been reported
from the United States on cattle, upon the skin of which they
form swellings. D. FOLLICULORUM Simon is the species found on
man. See page 78.
aa. Abdomen not annulate nor prolonged behind; eight legs in the adult
stage.
b. With a distinct spiracle upon a stigmal plate on each side of the
body (usually ventral) above the third or fourth coxae or a little
behind (fig. 50); palpi free; skin often coriaceous or leathery;
tarsi often with a sucker.
c. Hypostome large (fig. 50), furnished below with many recurved
teeth; venter with furrows, skin leathery; large forms, usually
parasitic. IXODOIDEA
d. Without scutum but covered by a more or less uniform leathery
integument; festoons absent; coxae unarmed, tarsi without
ventral spurs; pulvilli absent or vestigial in the adults;
palpi cylindrical; sexual dimorphism slight. ARGASIDAE
e. Body flattened, oval or rounded, with a distinct flattened
margin differing in structure from the general integument;
this margin gives the body a sharp edge which is not
entirely obliterated even when the tick is full fed.
Capitulum (in adults and nymphs) entirely invisible
dorsally, distant in the adult by about its own length from
the anterior border. Eyes absent. ARGUS Latr.
f. Body oblong; margin with quadrangular cells; anterior tibiae
and metatarsi each about three times as long as broad. On
poultry, southwest United States. A. PERSICUS MINIATUS
_A. brevipes_ Banks, a species with proportionately shorter
legs has been recorded from Arizona.
ff. With another combination of characters. About six other
species of _Argas_ from various parts of the world,
parasitic on birds and mammals.
ee. Body flattened when unfed, but usually becoming very convex
on distention; anterior end more or less pointed and
hoodlike; margin thick and not clearly defined, similar in
structure to the rest of the integument and generally
disappearing on distention; capitulum subterminal, its
anterior portions often visible dorsally in the adult; eyes
present in some species.
f. Integument pitted, without rounded tubercles; body provided
with many short stiff bristles; eyes absent. On horses,
cattle and man (fig. 48). OTIOBIUS Banks.
O. MEGNINI, a widely distributed species, is the type of
this genus.
ff. Integument with rounded tubercles or granules; body
without stiff bristles. ORNITHODOROS Koch.
g. Two pairs of eyes; tarsi IV with a prominent subterminal
spur above; leg I strongly roughened. On cattle and man.
O. CORIACEUS
gg. No eyes; no such spur on the hind tarsi.
h. Tarsi I without humps above. _O. talaje._
hh. Tarsi I with humps above.
i. Tarsi IV without distinct humps above. On hogs,
cattle and man. O. TURICATA
ii. Tarsi IV with humps nearly equidistant (fig. 142).
Africa. O. MOUBATA
[Illustration: 149. Haemaphysalis wellingtoni. Note short palpi. After
Nuttall and Warburton.]
dd. With scutum or shield (fig. 50); festoons usually present;
coxae usually armed with spurs, tarsi generally with one or two
ventral spurs; pulvilli present in the adults; sexual
dimorphism pronounced. IXODIDAE
e. With anal grooves surrounding anus in front; inornate;
without eyes; no posterior marginal festoons; venter of the
male with non-salient plates. Numerous species, 14 from the
United States, among them I. RICINUS (fig. 49 and 50),
SCAPULARIS, COOKEI, _hexagonus_, _bicornis_. IXODES Latr.
(including Ceratixodes).
ee. With anal groove contouring anus behind, or groove faint or
obsolete.
f. With short palpi (fig. 149).
g. Without eyes, inornate, with posterior marginal festoons;
male without ventral plates. Numerous species. _H.
chordeilis_ and _leporis-palustris_ from the United
States. _Haemaphysalis_ Koch.
[Illustration: 150. Stigmal plate of Dermacentor andersoni; (_a_) of
male, (_b_) of female. After Stiles. (_c_) Dermacentor variabilis, male;
(_d_) Glyciphagus obesus; (_e_) Otodectes cynotis; (_f_) Tyroglyphus
lintneri; (_g_) Tarsonemus pallidus; (_h_) anal plate and mandible of
Liponyssus; (_c_) to (_h_) after Banks.]
gg. With eyes.
h. Anal groove distinct; posterior marginal festoons
present.
i. Base of the capitulum (fig. 150c) rectangular
dorsally; usually ornate. DERMACENTOR Koch.
j. Adults with four longitudinal rows of large
denticles on each half of hypostome; stigmal plate
nearly circular, without dorso-lateral
prolongation, goblets very large, attaining 43u to
115u in diameter; not over 40 per plate, each
plate surrounded by an elevated row of regularly
arranged supporting cells; white rust wanting;
base of capitulum distinctly broader than long,
its postero-lateral angles prolonged slightly, if
at all; coxae T with short spurs; trochanter I with
small dorso-terminal blade. Texas, Arizona, etc.
_D. nitens_
[Illustration: 151. Rhipicephalus bursa, male. After Nuttall and
Warburton.]
jj. Adults with three longitudinal rows of large
denticles on each half of hypostome; goblet cells
always more than 40 per plate; whitish rust
usually present.
k. Dorso-lateral prolongation of stigmal plate small
or absent; plates of the adults distinctly
longer than broad; goblet cells large, usually
30u to 85u in diameter, appearing as very coarse
punctations on untreated specimens, but on
specimens treated with caustic potash they
appear very distinct in outline; base of
capitulum distinctly (usually about twice)
broader than long, the postero-lateral angles
distinctly produced caudad; spurs of coxae I
long, lateral spur slightly longer than median;
trochanter I with dorso-terminal spur. _D.
albipictus_, (= _variegatus_), _salmoni_,
_nigrolineatus_.
kk. Dorso-lateral prolongation of stigmal plate
distinct.
l. Body of plate distinctly longer than broad;
goblet cells of medium size, usually 17.5u to
35u or 40u in diameter, appearing as medium
sized punctuations on untreated specimens, but
on the specimens treated with caustic potash
they appear very distinct in outline, which is
not circular; base of capitulum usually less
than twice as broad as long, the
postero-lateral angles always distinctly
prolonged caudad.
m. Trochanter I with distinct dorso-subterminal
retrograde sharp, digitate spur;
postero-lateral angles of capitulum
pronouncedly prolonged caudal, 112u to 160u
long; goblet cells attain 13u to 40u in
diameter; type locality California. D.
OCCIDENTALIS
mm. Trochanter I with dorso-terminal blade;
postero-lateral angles of capitulum with
rather short prolongations.
n. Stigmal plate small, goblet cells not
exceeding 45 in the male or 100 in the
female; scutum with little rust, coxa I
with short spurs, the inner distinctly
shorter than the outer. _D.
parumapertus-marginatus_
nn. Stigmal plate larger; goblet cells over 70
in the male and over 100 in the female;
coxa I with longer spurs, inner slightly
shorter than the outer; scutum with
considerable rust. D. VENUSTUS[F]
ll. Goblet cells small, rarely exceeding 17.6u,
occasionally reaching 19u in diameter; on
untreated specimens they appear as very fine
granulations, and on specimens treated with
caustic potash they may be difficult to see,
but their large number can be determined from
the prominent stems of the goblets; surface of
outline of the goblets distinctly circular;
base of the capitulum usually less than twice
as broad as long, the postero-lateral angle
distinctly prolonged caudad; spurs of coxae I
long. _D. reticulatus_ and _electus_ (=
_variabilis_?)
ii. Base of the capitulum (fig. 151) usually hexagonal
(except in the male of _puchellus_); and usually
inornate.
j. No ventral plate or shield in either sex (fig.
153). R. BICORNIS from the United States.
RHIPICENTOR Nuttall
jj. Males with a pair of adanal shields, and usually a
pair of accessory adanal shields. Numerous
species, among them _R. sanguineus_ (fig. 154) and
_texanus_, the latter from the United States.
_Rhipicephalus_ Koch
hh. Anal grooves faint or obsolete; no marginal festoons.
i. Short palpi; highly chitinized; unfed adults of large
size; coxae conical; male with a median plate
prolonged in two long spines projecting caudad;
segments of leg pair IV greatly swollen (fig. 155,
156). _M. winthemi_ _Margaropus_ Karsch
[Illustration: 152. Monieziella (Histiogaster) emtomophaga-spermatica,
ventral aspect, male and female. After Trouessart.]
ii. Very short palpi, ridged dorsally and laterally;
slightly chitinized; unfed adults of smaller size;
coxae I bifid; male with adanal and accessory adanal
shields (fig. 139). B. ANNULATUS. BOOPHILUS Curtis
ff. Palpi longer than broad (fig. 157).
g. Male with pair of adanal shields, and two posterior
abdominal protrusions capped by chitinized points;
festoons present or absent. Several species, among them
H. AEGYPTICUM (fig. 140) from the old world. HYALOMMA
Koch
gg. Male without adanal shields but small ventral plaques
are occasionally present close to the festoons. Many
species, a few from the United States (fig. 157).
AMBLYOMMA Koch
h. Coxa I with but one spine; metatarsi (except I) with
two thickened spurs at tips. _A. maculatum_
hh. Coxa I with two spines; metatarsi without stout spurs
at tips, only slender hairs.
i. Projections of coxa I blunt and short. Large species
on the gopher tortoise in Florida. _A. tuberculatum_
ii. Projections of coxa I longer, and at least one of
them sharp pointed; second segment of palpus twice
as long as the third; coxa IV of the male with a
long spine.
j. Porose areas nearly circular; shield of both sexes
pale yellowish, with some silvery streaks and
marks, and some reddish spots; shield of female as
broad as long. A. CAJENNENSE (= MIXTUM).
jj. Porose areas elongate, shield brown, in the female
with an apical silvery mark, in the male with two
small and two or four other silvery spots; shield
of the female longer than broad (fig 158 e). A.
AMERICANUM.
[Illustration: 153. Rhipicentor bicornis, ventral aspect, male. After
Nuttall and Warburton.]
cc. Hypostome small, without teeth, venter without furrows; body
often with coriaceous shields, posterior margin of the body
never crenulate (i.e. without festoons); no eyes. GAMASOIDEA.
d. Parasitic on vertebrates; mandibles fitted for piercing; body
sometimes constricted. DERMANYSSIDAE.
e. Anal plate present. DERMANYSSINAE.
f. Body short; legs stout, hind pair reaching much beyond the
tip of the body. On bats. _Pteroptus_ Dufour.
ff. Body long; hind legs not reaching beyond the tip of the
body.
g. Peritreme on the dorsum, very short; body distinctly
constricted. _Ptilonyssus_ Berl.
gg. Peritreme on the venter, longer; body not distinctly
constricted.
h. Mandibles in both sexes chelate. Parasitic on bats,
mice and birds (fig. 150, h). LIPONYSSUS Kol.
The species L. (= LEIOGNATHUS) SYLVIARUM frequents the
nests of warblers. An instance is on record of
these mites attacking man, causing a pruritis.
hh. Mandibles in the male chelate (fig. 158 j), in the
female long, styliform. Parasitic on birds.
DERMANYSSUS Dug. Two species of importance may be
noted, _D. hirundinus_ and D. GALLINAE. The latter
(fig. 51) is a serious pest of poultry, sometimes
attacking man, causing itching and soreness.
ee. Anal plate absent. In lungs and air passages of some
mammals. HALARACHNINAE.
dd. Free or attached to insects, rarely on vertebrates.
e. First pair of legs inserted within the same body opening as
the oral tube; genital apertures surrounded by the sternum.
On insects. UROPODIDAE.
[Illustration: 154. Rhicephalus sanguineus, male. After Nuttall and
Warburton.]
ee. First pair of legs inserted at one side of the mouth
opening; male genital aperture usually on the anterior
margin of the sternal plate. GAMASIDAE.
This family contains a number of genera, some of which are
found upon mammals, though the majority affect only other
arthropods. One species, LAELAPS STABULARIS, frequents the
bedding in stables, and in one instance at least, has
occasioned irritation and itching, in man.
bb. No distinct spiracle in the stigmal plate on each side of the
body.
c. Body usually coriaceous, with few hairs, with a specialized seta
arising from a pore near each posterior corner of the
cephalothorax; no eyes; mouth parts and palpi very small;
ventral openings of the abdomen large; tarsi without sucker. Not
parasitic. ORIBATOIDEA.
cc. Body softer; without such specialized seta.
d. Aquatic species. HYDRACHNOIDEA.
dd. Not aquatic.
e. Palpi small, three segmented, adhering for some distance to
the lip; ventral suckers at genital opening or near anal
opening usually present; no eyes; tarsi often end in
suckers; beneath the skin on the venter are seen rod-like
epimera that support the legs; body often entire. Adults
frequently parasitic. SARCOPTOIDEA.
f. With tracheae; no ventral suckers; legs ending in claws;
body divided into cephalothorax and abdomen; the female
with a clavate hair between legs I and II. Usually not
parasitic on birds and mammals. TARSONEMIDAE
g. Hind legs of female ending in claw and sucker as in the
other pairs. PEDICULOIDINAE
To this sub-family belongs the genus PEDICULOIDES
P. ventricosus is described on page 69.
[Illustration: 155. Margaropus winthemi, male. After Nuttall and
Warburton.]
[Illustration: 156. Margaropus winthemi, capitulum and scutum.
After Nuttall and Warburton.]
gg. Hind legs of the female end in long hairs. TARSONEMINAE
TARSONEMUS INTECTUS Karpelles, normally found upon grain,
is said to attack man in Hungary and Russia. Other
species of the genus affect various plants (c.f. fig.
150, g).
ff. Without tracheae; no such clavate hair.
g. Genital suckers usually present; integument usually
without fine parallel lines.
h. Legs short, without clavate hair on tarsi I and II. On
insects. CANESTRINIDAE.
hh. Legs longer, with a clavate hair on tarsi I and II.
Not normally parasitic except on bees. TYROGLYPHIDAE
i. Dorsal integument more or less granulate; claws very
weak, almost invisible; some hairs of the body
plainly feathered; ventral apertures large.
GLYCIPHAGUS Her.
This genus occurs in the United States. In Europe the
mites have been found feeding on all sorts of
substances. They are known as sugar mites and
cause the disease known as grocer's itch. G.
DOMESTICUS and G. PRUNORUM are old world species
(fig. 150, d).
ii. Dorsal integument not granulate; claws distinct; no
prominent feathered hairs; ventral aperture small.
j. Mandibles not chelate; elongate, and toothed below;
body without long hairs; palpi enlarged at tip and
provided with two divergent bristles. Species feed
on decaying substances. _Histiostoma_ Kram.
jj. Mandibles chelate; palpi not enlarged at the tip,
nor with two bristles.
k. No clavate hair on the base of tarsi I and II; no
suture between cephalothorax and abdomen. Live
on bees or in their nests. _Trichotarsus_ Can.
kk. A clavate or thickened hair at the base of tarsi
I and II.
l. The bristle on the penultimate segment of the
legs arises from near the middle; no suture
between the cephalothorax and abdomen. The
species, some of which occur in the United
States, feed on dried fruit, etc.
_Carpoglyphus_ Robin.
ll. The bristle on the penultimate segment of the
legs arise from near the tip; a suture between
cephalothorax and abdomen.
m. Cephalothorax with four distinct and long
bristles in a transverse row; tarsi I and II
about twice as long as the preceding segment
(fig. 150 f). TYROGLYPHUS Latr.
n. Some bristles on tarsi I and II near
middle, distinctly spine-like; the sense
hair about its length from the base of the
segment. Several species in the United
States belong to this group.
nn. No spine-like bristles near the middle of
the tarsi; sense hair not its length from
the base of the segment.
o. Of the terminal abdominal bristles, only
two are about as long as the abdomen;
leg I of the male greatly thickened and
with a spine at apex of the femur below.
T. FARINAE.
oo. Of the terminal abdominal bristles at
least six or more are very long, nearly
as long as the body.
p. Bristles of the body distinctly plumose
or pectinate; tarsi very long. T.
LONGIOR.
pp. Bristles of the body not pectinate.
q. In mills, stored foods, grains, etc.
Third and fourth joints of hind legs
scarcely twice as long as broad;
abdominal bristles not unusually
long; legs I and II of the male not
unusually stout. T. AMERICANUS.
qq. With other characters and habits.
_T. lintneri_ (fig. 150 f) the
mushroom mite, and several other
species.
mm. Cephalothorax with but two long distinct
bristles (besides the frontal pair), but
sometimes a very minute intermediate pair;
tarsi I and II unusually short and not twice
as long as the preceding segment.
n. Tarsi with some stout spines. RHIZOGLYPHUS
Clap.
The species of this genus are vegetable
feeders. Several occur in the United
States. R. PARASITICUS and R.
SPINITARSUS have been recorded from the
old world, attacking human beings who
handle affected plants.
nn. Tarsi with only fine hairs. MONIEZIELLA
Berl.
The species of this genus, as far as known,
are predaceous or feed on recently
killed animal matter. Several species
occur in the United States. M. (=
HISTIOGASTER) ENTOMOPHAGA (fig. 152)
from the old world has been recorded as
injurious to man.
gg. Genital suckers absent; integument with fine parallel
lines. Parasitic on birds and mammals.
h. Possessing a specially developed apparatus for clinging
to hairs of mammals. LISTROPHORIDAE.
hh. Without such apparatus.
i. Living on the plumage of birds. ANALGESIDAE.
ii. In the living tissues of birds and mammals.
j. Vulva longitudinal. In the skin and cellular
tissues of birds. CYTOLEICHIDAE.
This family contains two species, both occurring in
the United States on the common fowl.
_Laminosioptes cysticola_ occurs on the skin and
also bores into the subcutaneous tissue where it
gives rise to a calcareous cyst. _Cytoleichus
nudus_ is most commonly found in the air
passages and air cells.
jj. Vulva transverse. In the skin of mammals and
birds. SARCOPTIDAE
k. Anal opening on the dorsum.
l. Third pair of legs in the male without apical
suckers. On cats and rabbits. NOTOEDRES
Rail.
The itch mite of the cat, N. CATI (fig. 61) has
been recorded on man.
ll. Third leg in the male with suckers. On bats
_Prosopodectes_ Can.
kk. Anal opening below.
l. Pedicel of the suckers jointed; mandibles
styliform and serrate near the tip. PSOROPTES
Gerv. P. COMMUNIS OVIS is the cause of sheep
scab.
ll. Pedicel of the suckers not jointed; mandibles
chelate.
m. No suckers on the legs of the females;
parasitic on birds, including chickens. _C.
mutans_ is itch mite of chickens.
_Cnemidocoptes_ Furst.
mm. Suckers at least on legs I and II; parasitic
on mammals.
n. Legs very short; in the male the hind pairs
equal in size; body usually short.
SARCOPTES Latr.
S. SCABIEI is the itch mite of man (fig.
56).
[Illustration: 157. Amblyomma, female. After Nuttall and Warburton.]
nn. Legs more slender; in the male the third
pair is much larger than the fourth; body
more elongate.
o. Female with suckers on the fourth pair of
legs. Species do not burrow in the skin,
but produce a scab similar to sheep
scab. They occur in the ox, horse, sheep
and goat. CHORIOPTES Gerv. C. SYMBIOTES
BOVIS of the ox has been recorded a few
times on man.
oo. Female without suckers to the fourth
legs.
p. Hind part of the male abdomen with two
lobes. On a few wild animals.
_Caparinia_ Can.
pp. Hind part of the male abdomen without
lobes. Live in ears of dogs and cats.
_Otodectes_ Canestr.
_O. cynotis_ Hering (fig. 150 e) has
been taken in the United States.
ee. Palpi usually of four or five segments, free; rarely with
ventral suckers near genital or anal openings; eyes often
present; tarsi never end in suckers; body usually divided
into cephalothorax and abdomen; rod-like epimera rarely
visible; adults rarely parasitic.
f. Last segment of the palpi never forms a thumb to the
preceding segment; palpi simple, or rarely formed to hold
prey; body with but few hairs. EUPODOIDEA.
g. Palpi often geniculate, or else fitted for grasping prey;
mandibles large and snout like; cephalothorax with four
long bristles above, two in front, two behind; last
segment of leg I longer than the preceding segment,
often twice as long. BDELLIDAE.
gg. Palpi never geniculate (fig. 158a), nor fitted for
grasping prey: beak small; cephalothorax with bristles
in different arrangement; last segment of leg I shorter
or but little longer than the preceding joint; eyes when
present near posterior border. EUPODIDAE
Moniez has described a species from Belgium (TYDEUS
MOLESTUS) which attacks man. It is rose colored;
eyeless; its legs are scarcely as long as its body,
the hind femur is not thickened; the mandibles are
small and the anal opening is on the venter. The
female attains a length of about 0.3 mm.
ff. Last segment of the palpus forms a thumb to the preceding,
which ends in a claw (with few exceptions); body often
with many hairs (fig. 158 k). TROMBIDOIDEA.
g. Legs I and II with processes bearing spines; skin with
several shields; coxae contiguous. CAECULIDAE.
gg. Legs I and II without such processes; few if any
shields.
h. Palpi much thickened on the base, moving laterally,
last joint often with two pectinate bristles; no eyes;
legs I ending in several long hairs; adult sometimes
parasitic. CHEYLETIDAE
CHEYLETUS ERUDITUS, which frequents old books, has once
been found in pus discharged from the ear of man.
hh. Palpi less thickened, moving vertically; eyes usually
present; leg I not ending in long hairs.
i. Coxae contiguous, radiate; legs slender, bristly; body
with few hairs; no dorsal groove; tarsi not swollen.
ERYTHRAEIDAE.
ii. Coxae more or less in two groups; legs less bristly.
[Illustration: 158. (_a_) Tydeus, beak and leg from below; (_b_)
Cheyletus pyriformis, beak and palpus; (_c_) beak and claw of
Pediculoides; (_d_) leg of Sarcoptes; (_e_) scutum of female of
Amblyomma americana; (_f_) leg I and tip of mandible of Histiostoma
americana; (_g_) Histiogaster malus, mandible and venter; (_h_)
Aleurobius farinae, palpus and leg I of male; (_i_) Otodectes cynotis,
tip of abdomen of male, (_j_) beak and anal plate of Dermanyssus
gallinae female; (_k_) palpus of Allothrombium. (_a_) to (_j_) after
Banks.]
j. Body with fewer, longer hairs; often spinning
threads; no dorsal groove; tarsi never swollen;
mandibles styliform (for piercing). TETRANYCHIDAE
The genus TETRANYCHUS may be distinguished from the
other genera occurring in the United States by
the following characters: No scale-like
projections on the front of the cephalothorax;
legs I as long or longer than the body; palp
ends in a distinct thumb; the body is about 1.5
times as long as broad. T. MOLESTISSIMUS Weyenb.
from South America, and T. TELARIUS from Europe
and America ordinarily infesting plants, are
said also to molest man.
jj. Body with many fine hairs or short spines; not
spinning threads; often with dorsal groove; tarsi
often swollen.
k. Mandibles styliform for piercing. RHYCHOLOPHIDAE.
kk. Mandibles chelate, for biting. TROMBIDIDAE
The genus TROMBIDIUM has recently been subdivided
by Berlese into a number of smaller ones, of
which some five or six occur in the United
States. The mature mite is not parasitic but
the larvae which are very numerous in certain
localities will cause intense itching,
soreness, and even more serious complications.
They burrow beneath the skin and produce
inflamed spots. They have received the popular
name of "RED BUG." The names LEPTUS AMERICANUS
and L. IRRITANS have been applied to them,
although they are now known to be immature
stages. (Fig. 44.)
HEXAPODA (Insecta)
The Thysanura (springtails and bristletails), the Neuropteroids
(may-flies, stone-flies, dragon-flies, caddis-flies, etc.), Mallophaga
(bird lice), Physopoda (thrips), Orthoptera (grasshoppers, crickets,
roaches), are of no special interest from our viewpoint. The remaining
orders are briefly characterized below.
SIPHUNCULATA (page 275)
Mouth parts suctorial; beak fleshy, not jointed; insect wingless;
parasitic upon mammals. Metamorphosis incomplete. Lice.
HEMIPTERA (page 275)
Mouth parts suctorial; beak or the sheath of the beak jointed; in the
mature state usually with four wings. In external appearance the
immature insect resembles the adult except that the immature form (i.e.
nymph) never has wings, the successive instars during the process of
growth, therefore, are quite similar; and the metamorphosis is thus
incomplete. To this order belong the true bugs, the plant lice, leaf
hoppers, frog hoppers, cicadas, etc.
LEPIDOPTERA
The adult insect has the body covered with scales and (with the rare
exception of the females of a few species) with four wings also covered
with scales. Proboscis, when present, coiled, not segmented, adapted for
sucking. Metamorphosis complete, i.e. the young which hatches from the
egg is quite unlike the adult, and after undergoing several molts
transforms into a quiescent pupa which is frequently enclosed in a
cocoon from which the adult later emerges. The larvae are known as
caterpillars. Butterflies and moths.
DIPTERA (page 285)
The adult insect is provided with two, usually transparent, wings, the
second pair of wings of other insects being replaced by a pair of
halteres or balancers. In a few rare species the wings, or halteres, or
both, are wanting. The mouth parts, which are not segmented, are adapted
for sucking. The tarsi are five-segmented. Metamorphosis complete. The
larvae, which are never provided with jointed legs, are variously known
as maggots, or grubs, or wrigglers. Flies, midges, mosquitoes.
SIPHONAPTERA (page 316)
Mouth parts adapted for sucking; body naked or with bristles and spines;
prothorax well developed; body compressed; tarsi with five segments;
wings absent. Metamorphosis complete. The larva is a wormlike creature.
Fleas.
COLEOPTERA
Adult with four wings (rarely wanting), the first pair horny or
leathery, veinless, forming wing covers which meet in a line along the
middle of the back. Mouth parts of both immature stages and adults
adapted for biting and chewing. Metamorphosis complete. The larvae of
many species are known as grubs. Beetles.
HYMENOPTERA
Adult insect with four, usually transparent, wings, wanting in some
species. Mouth parts adapted for biting and sucking; palpi small; tarsi
four or five-segmented. Metamorphosis complete. Parasitic four-winged
flies, ants, bees, and wasps.
SIPHUNCULATA AND HEMIPTERA
a. Legs with claws fitted for clinging to hairs; wings wanting;
spiracles of the abdomen on the dorsal surface. (= ANOPLURA =
PARASITICA) SIPHUNCULATA.
b. Legs not modified into clinging hooks; tibia and tarsus very long
and slender; tibia without thumb-like process; antennae
five-segmented. HAEMATOMYZIDAE Endr.
_Haematomyzus elephantis_ on the elephant.
bb. Legs modified into clinging hooks; tibia and tarsus usually short
and stout; tibia with a thumb-like process; head not anteriorly
prolonged, tube-like.
c. Body depressed; a pair of stigmata on the mesothorax, and
abdominal segments three to eight; antennae three to
five-segmented.
d. Eyes large, projecting, distinctly pigmented; pharynx short and
broad; fulturae (inner skeleton of head) very strong and broad,
with broad arms; proboscis short, scarcely attaining the
thorax. PEDICULIDAE
e. Antennae three-segmented. A few species occurring upon old
world monkeys. _Pedicinis_ Gerv.
ee. Antennae five-segmented.
f. All legs stout; thumb-like process of the tibia very long
and slender, beset with strong spines, fore legs stouter
than the others; abdomen elongate, segments without
lateral processes; the divided telson with a conical
process posteriorly upon the ventral side. PEDICULUS L.
g. Upon man.
h. Each abdominal segment dorsally with from one to three
more or less regular transverse rows of small setae;
antenna about as long as the width of the head. Head
louse (fig. 65). P. HUMANUS.
hh. "No transverse rows of abdominal setae; antenna longer
than the width of the head; species larger." Piaget.
Body louse of man. P. CORPORIS.
gg. Upon apes and other mammals. _P. pusitatus_ (?).
ff. Fore legs delicate, with very long and slender claws;
other legs very stout with short and stout claws;
thumb-like process of the tibia short and stout; abdomen
very short and broad; segment one to five closely crowded,
thus the stigmata of segments three to five apparently
lying in one segment; segments five to eight with lateral
processes; telson without lateral conical appendages (fig.
69). Crab louse of man. PHTHIRUS PUBIS.
dd. Eyes indistinct or wanting; pharynx long and slender, fulturae
very slender and closely applied to the pharynx; proboscis
very long. Several genera found upon various mammals.
HAEMATOPINIDAE.
cc. Body swollen; meso- and metathorax, and abdominal segments two
to eight each with a pair of stigmata; eyes wanting; antennae
four or five-segmented; body covered with stout spines. Three
genera found upon marine mammals. ECHINOPHTHIRIIDAE
aa. Legs fitted for walking or jumping; spiracles of abdomen usually
ventral; beak segmented.
b. Apex of head usually directed anteriorly; beak arising from its
apex; sides of the face remote from the front coxae; first pair of
wings when present thickened at base, with thinner margins.
HETEROPTERA
[Illustration: 159. Taxonomic details of Hemiptera-Heteroptera. (_a_)
Dorsal aspect; (_b_) seta from bedbug; (_c_) wing of Heteropteron; (_d_)
leg; (_e_) wing of Sinea.]
c. Front tarsi of one segment, spade-form (palaeformes); beak short,
at most two-segmented; intermediate legs long, slender;
posterior pair adapted for swimming. CORIXIDAE
cc. Front tarsi rarely one-segmented, never spade-form; beak free,
at least three-segmented.
d. Pulvilli wanting.
e. Hemelytra usually with a distinct clavus (fig. 159), clavus
always ends behind the apex of the scutellum, forming the
commissure. (Species having the wings much reduced or
wanting should be sought for in both sections.)
f. Antennae very short; meso- and metasternum composite; eyes
always present.
g. Ocelli present; beak four-segmented. OCHTERIDAE and
NERTHRIDAE.
gg. Ocelli wanting; antennae more or less hidden in a groove.
h. Anterior coxae inserted at or near anterior margin of
the prosternum; front legs raptorial; beak
three-segmented BELOSTOMIDAE (with swimming legs),
NEPIDAE, NAUCORIDAE.
i. Metasternum without a median longitudinal keel;
antennae always four-segmented.
j. Beak short, robust, conical; the hairy fleck on the
corium elongate, large, lying in the middle
between the inner angle of the membrane and the
outer vein parallel to the membrane margin;
membrane margin S-shaped.
k. The thick fore femur with a relatively deep
longitudinal furrow to receive the tibia.
Several American species (fig. 19f.). BELOSTOMA
(= Lethocerus Mayer)
kk. The less thickened fore femur without such a
furrow. B. GRISEUS. BENACUS Stal.
jj. Beak slender, cylindrical; the hairy spot on the
corium rounded lying next to the inner angle of
the membrane.
k. Membrane large, furrow of the embolium broadened.
_Z. aurantiacum_, _fluminea_, etc. _Zaitha_
kk. Membrane very short; furrow of embolium not
broadened. Western genus. _Pedinocoris_
ii. Metasternum with a long median longitudinal keel.
Southwestern forms. _Abedus ovatus_ and _Deniostoma
dilatato_
hh. Anterior coxae inserted at the posterior margin of the
prosternum; legs natatorial. Back swimmers (fig. 19 b.).
NOTONECTIDAE
i. Apices of the hemelytra entire; the three pairs of legs
similar in shape; beak three-segmented; abdomen not
keeled or hairy. _Plea_ Leach
ii. Apices of hemelytra notched; legs dissimilar; beak
four-segmented; abdomen keeled and hairy.
j. Hemelytra usually much longer than the abdomen;
fourth segment of the antenna longer than the third
segment; hind tarsi with claws. _Bueno_ Kirk.
jj. Hemelytra but little longer than the abdomen; fourth
segment of the antenna shorter than the third
segment; hind tarsi without claws (fig. 19b).
NOTONECTA L.
ff. Antennae longer than the head; or if shorter, then the eyes
and ocelli absent.
g. Eyes, ocelli, and scutellum wanting; beak
three-segmented; head short; hemelytra always short;
membrane wanting. Insects parasitic on bats. POLYCTENIDAE
gg. Eyes present.
h. First two antennal segments very short, last two long,
pilose, third thickened at the base; ocelli present,
veins of the hemelytra forming cells. DIPSOCORIDAE (=
CERATOCOMBIDAE) including SCHIZOPTERIDAE.
hh. Third segment of the antenna not thickened at the
base, second as long or longer than the third, rarely
shorter.