────────────────────────────────────────────┬──────────────────────
Fig. 1. Clasping organs of male │F Finger.
„ │M Manubrium.
„ │IX St Ninth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 2. Head of male. │
────────────────────────────────────────────┼──────────────────────
Fig. 3. Terminal abdominal segments, female │8 T Eighth Tergite.
„ │8 St Eighth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 4. Hind coxa and femur, inner surface. │
CTENOCEPHALUS CANIS Curtis.
[Plate VI.]
_Head._—Strongly and evenly rounded in both sexes. Eye large. Maxilla
triangular. Maxillary palpi about as long as labial palpi. Labial
palpi reach to two-thirds of anterior coxæ, 4-jointed. Seven spines
along the lower margin of the gena. The posterior angle of the gena
ends in a small tooth. Occasionally this may be absent. Antennal
groove in the female reaches to within one-third of the top of head
and is prolonged upwards by a chitinous thickening and in the male
reaches almost to top of head. Two bristles on the gena, one placed
well toward the anterior lower angle and the other in front of the
eye. Usual number of bristles on posterior margin of the head, with 2
large ones back of the antennal groove. About 8 hairs on the second
joint of the antenna nearly as long as the third joint.
_Thorax._—A row of about 10 bristles on the pronotum, with a ctenidium
of about 14 to 16 spines. Two rows of bristles on the mesonotum, a
posterior of about 12, another of more numerous smaller bristles
placed well anteriorly. The metanotum contains a single row of about
10 or 12 bristles. The episternum of the metathorax has 3 or 4 stout
bristles, while the epimerum contains an anterior row of about 10
bristles and a posterior row of about 9.
_Abdomen._—The first abdominal tergite contains 2 rows of about 4
bristles each, while the other tergites to the seventh contain a
single row of from 12 to 16 bristles. The stigmata are large. There is
a single antipygidial bristle on each side. The sternites from third
to seventh have a single row of 4 bristles each.
_Legs._—The hind coxa has on its inner side a patch of from 6 to 12
spines, while the hind femur has a row of 10 or 12 bristles on its
inner surface. The spines on the posterior border of the hind tibia,
with the exception of the apical, are in pairs, while in the apical
group are about 3 stout bristles. The apical spine of the second joint
of the hind leg reaches to nearly the middle of the fifth joint. On
the fifth joint of all the legs there are 4 lateral spines and a
subapical pair, and between the third and fourth lateral spines there
is a hair.
_Modified segments._—(♀) The eighth tergite has no hairs back of the
stigma. The apical margin is rounded at the apex and contains 8 or 10
bristles. The stylet is short and wide and contains at its tip a long
and a short bristle.
(♂) The manubrium is short and narrow. The movable finger of the
clasper is short, thick, swollen at its middle, bluntly rounded at its
extremity, and contains on its upper border numerous hairs and a few
on its lower border.
Rothschild[209] has pointed out certain differences between the
_Ctenocephalus canis_ and _Ctenocephalus felis_. The differences are
that in the female of the felis the head is longer and more pointed.
This difference is not so pronounced in the male. Also certain
differences in the shape of the claspers and the number of bristles in
the episternum and epimerum of the metathorax and the hind femur,
those in the _C. canis_ being more numerous. Also that group of
bristles on the posterior border of the hind tibia between the fifth
pair and the apical bristles consists of two in the _Ctenocephalus
canis_, while there is but a single bristle with a small hair in the
_Ctenocephalus felis_.
REFERENCES.
Endnote 201:
1909, McCoy.—“Plague Bacilli in Ectoparasites of Squirrels.” Public
Health Reports, Vol. XXIV, No. 16.
Endnote 202:
1908, Schumann.—“A Disease of Rats Caused by Mites.” Centralblatt f.
Bact., Oct. 30th.
Endnote 203:
1909, McCoy and Mitzmain.—“An Experimental Investigation of the
Biting of Man by Fleas Taken from Rats and Squirrels.” Public Health
Reports, Vol. XXIV, No. 8.
Endnote 204:
1908, McCoy.—“A Report on Laboratory Work in Relation to the
Examination of Rats for Plague at San Francisco, California.” Public
Health Reports, Vol. XXIII, No. 30.
Endnote 205:
Wagner.—Aphanipterologische Studien aus dem zootomischen
laboratorium der Universität zu St. Petersburg.
Endnote 206:
1908, Mitzmain.—“How a Hungry Flea Feeds.” Entomological News,
December.
Endnote 207:
1908, Miller.—“Hepatazoon Perniciosum (N. G. N. SP.). A
Hæmogregarine Pathogenic for White Rats; With a Description of the
Sexual Cycle in the Intermediate Host; A Mite (Lælaps Echidninus).”
Bull. No. 46, Hyg. Lab. U. S. Pub. Health and Mar. Hosp. Serv.,
Wash.
Endnote 208:
1908, Jordan and Rothschild.—“Revision of Non-Combed Eyed
Siphonaptera.” Parasitology, Vol. I, No. 1.
Endnote 209:
1901, Rothschild.—“Notes on Pulex canis, Curtis, and Pulex felis,
Bouché.” Entomologist’s Record, Vol. XIII, No. 4.
1905, Rothschild.—“Some Further Notes on Pulex canis, Curtis, and
Pulex felis, Bouché.” Novitates Zoologicae, Vol. XII.
[Illustration:
PLATE VI.
CTENOCEPHALUS CANIS, CURTIS.
]
RODENTS IN RELATION TO THE TRANSMISSION OF BUBONIC PLAGUE.
By Surgeon RUPERT BLUE,
_United States Public Health and Marine-Hospital Service_.
Man has associated the rat with bubonic plague since the dawn of
history. The monuments and coins of the earliest times yield abundant
evidence of this association. Æsculapius, the god of the healing art,
is represented by the Greeks with a rat at his feet. An early
scriptural reference may be found in the first Book of Samuel in the
fifth and sixth chapters. The historian records therein the occurrence
of a fatal epidemic of “emerods” in the land of the Philistines
coincident with an invasion of “mice.”
The inhabitants of southern China in recent times have learned to look
upon the finding of sick and dead rats in their homes as a harbinger
of evil, in fact, as a forerunner of that dread scourge—“wan-yick,” or
plague. In the villages and cities of the Kwantung and Kwangsi
provinces, as recorded by medical missionaries, epizootic plague
almost invariably precedes an outbreak among human beings. So well is
this fact known to the common people that many seek safety in flight,
feeling assured that in a short time “yang-tzu” or “wan-yick” will
claim a harvest of victims among those who remain.
Doctor Mahē, sanitary officer for the port of Constantinople, in 1889,
called attention to the fact that epidemics of plague were always
announced by a great mortality among rats and mice. In 1894 Yersin
reported the fatal epizootic among rats then prevailing in Canton and
Hongkong coincident with the outbreak of plague among the Chinese.
Recent researches have confirmed these observations and a great deal
has been added to the literature of plague, especially in relation to
its mode of transmission. Indeed, it should be said that wherever the
disease has prevailed in recent years the relation of rats to its
spread has been observed, and that since the discovery of the specific
bacillus by Yersin and Kitasato, in 1894, bacteriological
investigations have shown that there is no difference morphologically
or culturally between the bacilli of human and rat plague. Moreover,
the gross and microscopic lesions in the lymph nodes are practically
the same, and the _B. pestis_ recovered in both fulfills the
postulates of Koch.
Nothing was definitely known, however, of the mode of transmission of
the disease from rat to rat or from rat to man until the completion of
the experimental work of the Indian Plague Commission. Simond, Ogata,
Thompson, and Koch each expressed the belief that the infection was
transferred by the rat flea. Nuttall (1897) and Simond (1898)
demonstrated the presence of _B. pestis_ in the bodies of bugs
(_Cimex_) and fleas which had been taken from plague-sick rats, and
the latter observer, in the same year, succeeded in transmitting the
disease from rat to rat without contact.
The work of the Indian Plague Commission was undertaken (1905) with a
view to establishing the exact relationship between epizootics among
rats and epidemics among men, and included both field and laboratory
observations. The experiments of Gauthier and Raybaud (1903) and of
Simond were repeated on a larger scale and greatly improved in that
all rats and fleas used were first identified as to species. The
findings of the commission may be briefly summarized as follows: That
fleas and bugs taken from plague-sick rats contain _B. pestis_, and
that some of them remain alive in the bodies of the insects from five
to sixteen days; that plague is conveyed by the bites of fleas which
have previously fed on the blood of animals suffering with the
disease; that rat fleas bite man; that under experimental conditions
the infection is not transferred from rat to rat in the absence of
fleas.
A careful study of the findings of the workers in India justifies the
assumption that plague is a disease of the rodent primarily and
accidentally, and secondarily a disease of man. An analysis of the
epidemiological facts collected in San Francisco leads to the same
conclusion. As a result our practice with regard to suppressive
measures and quarantine procedure has undergone a radical change in
the last decade. If the infection is flea-borne from rat to man in the
majority of cases, then the extermination of the rat should be the
first principle upon which to base a campaign. In the former
contribution on the subject (1907) I stated that “if we destroy the
host there is no longer danger of infecting the parasite.” This basic
principle has been recognized and successfully applied in two
campaigns against plague in San Francisco. First in the outbreak in
Chinatown in 1903–4, and again in the larger epidemic of 1907.
The outbreak of 1907 began May 27, a little over a year after the
great fire and earthquake, but no cases were discovered between that
time and mid-August when the disease began to appear in various parts
of the city. The source of infection was, in all probability, a
recrudescence from a focus which was not destroyed in the campaign of
1903–4. There occurred 160 cases with 77 deaths, the last case
appearing January 30, 1908. The following table shows the incidence of
human plague:
─────────────────────┬───────┬───────
Year. │Cases. │Deaths.
─────────────────────┼───────┼───────
1907. │ │
May │ 1│ 1
August │ 13│ 6
September │ 56│ 25
October │ 34│ 25
November │ 41│ 12
December │ 13│ 7
1908. │ │
January │ 2│ 1
─────────────────────┼───────┼───────
Total │ 160│ 77
─────────────────────┴───────┴───────
EPIDEMIOLOGICAL OBSERVATIONS IN SAN FRANCISCO.
Abundant epidemiological data associating the rat[AE] with plague have
been collected in San Francisco. For the purpose of illustration a
detailed reference to a few cases will be made. Two small boys
(October, 1907) while playing in an unused cellar found the body of a
dead rat. The corpse was buried with unusual funeral honors. In
forty-eight hours both were ill with bubonic plague. A laborer finding
a sick rat on the wharf picked it up with the naked hand and threw it
into the bay. He was seized three days later with plague. Doctor C.
and family lived in a second-story flat over a grocery store in the
residence section. Being annoyed for some days by a foul odor the
doctor caused the wainscoting around the plumbing to be removed. One
or two rat cadavers were found in the hollow wall. In two or three
days the two members of the family who used the room sickened, one
dying on the fifth day of cervical bubonic plague. It is probable that
infected rat fleas were set free by the removal of the wainscoting.
Footnote AE:
_M. norvegicus_ and _M. rattus_.
Dead rats were frequently found in or near houses where plague had
occurred. Immediately upon the discovery of a case of plague trained
men were sent into the neighborhood and a thorough search made for
rats. This work consisted in the removal of defective wooden floors
and walls of insanitary buildings and other harboring places.
Extensive rat catacombs were frequently found in these operations. In
the yard of a house in which 4 cases had occurred 20 cadavers were
found under the board covering. In the walls of a Chinese restaurant
87 dead rats were uncovered.
Very little can be said of the relation of mice (_M. musculus_) to the
epidemic. While many thousands were trapped, only a few hundred were
examined microscopically and in these no infection was found. They are
nonmigratory in habit and for this reason are not considered of much
importance from an epizoological standpoint.
Transmission from man to man was observed in but a small percentage of
cases, 3 per cent to be exact. In these the probability of
transference by fleas (_P. irritans_) or by bugs (_Cimex_) must be
admitted. When more than one case occurred in a house a common source
of infection was indicated, such cases occurring simultaneously or
within from forty-eight to seventy-two hours after the first.
Deratization was the measure mainly relied upon. After an infected
house was rat proofed, and the harboring places in the block
destroyed, no further cases occurred.
The course of epizootic plague was not interrupted at any time by
climatic conditions, there being as many cases in proportion to the
rat population in the winter of 1908 as there were at the height of
the epidemic. The last case of human plague occurred January 30, 1908,
but the infection remained active among rats for eight months longer,
or until October 21, 1908. (See following table.)
─────────┬─────────┬─────────┬─────┬────────────┬────────┬─────────────
Month. │ Number │ Number │ Per │ Average │Rainfall│Character of
│examined.│infected.│cent.│temperature.│ in │ days.
│ │ │ │ │inches. │
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
1907. │ │ │ │ °F. │ │{Clear, 13.
September│ 1,002│ 27│ 2.69│ 60.6│ 0.11│{Part cloudy,
│ │ │ │ │ │15.
│ │ │ │ │ │{Cloudy, 2.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 10.
October │ 2,679│ 23│ .86│ 60.6│ 1.36│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 11.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 14.
November │ 3,954│ 36│ .88│ 57.8│ .04│{Part cloudy,
│ │ │ │ │ │13.
│ │ │ │ │ │{Cloudy, 3.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 6.
December │ 4,308│ 48│ 1.11│ 52.4│ 3.66│{Part cloudy,
│ │ │ │ │ │11.
│ │ │ │ │ │{Cloudy, 14.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
1908. │ │ │ │ │ │{Clear, 5.
January │ 6,622│ 70│ 1.05│ 50.8│ 4.88│{Part cloudy,
│ │ │ │ │ │11.
│ │ │ │ │ │{Cloudy, 15.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 11.
February │ 11,700│ 45│ .38│ 51.0│ 5.39│{Part cloudy,
│ │ │ │ │ │12.
│ │ │ │ │ │{Cloudy, 6.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 20.
March │ 19,263│ 52│ .26│ 54.8│ .90│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 1.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 17.
April │ 15,524│ 34│ .21│ 56.3│ .22│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 3.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 17.
May │ 11,311│ 20│ .13│ 55.4│ .76│{Part cloudy,
│ │ │ │ │ │12.
│ │ │ │ │ │{Cloudy, 2.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 16.
June │ 13,624│ 4│ 0.02│ 55.3│ 0.01│{Part cloudy,
│ │ │ │ │ │9.
│ │ │ │ │ │{Cloudy, 5.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 11.
July │ 11,204│ 2│ .017│ 57.4│ .02│{Part cloudy,
│ │ │ │ │ │17.
│ │ │ │ │ │{Cloudy, 3.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 11.
August │ 10,988│ 0│ .0│ 57.3│ .01│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 10.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 16.
September│ 15,902│ 0│ .0│ 59.3│ .29│{Part cloudy,
│ │ │ │ │ │9.
│ │ │ │ │ │{Cloudy, 5.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 16.
October │ 10,178│ 2│ .019│ 58.8│ .061│{Part cloudy,
│ │ │ │ │ │7.
│ │ │ │ │ │{Cloudy, 8.
─────────┴─────────┴─────────┴─────┴────────────┴────────┴─────────────
The rats examined for September, 1907, were very largely collected
from the badly infected districts; the remaining months give a truer
picture of the extent of the epizootic in the entire rat population.
THEORIES AS TO THE CAUSE OF SEASONAL PREVALENCE.
The marked seasonal prevalence of plague in man in San Francisco may
be given as additional proof of the association of the rat with its
spread. In the cold, rainy season, from December to April, the
epidemic ceases while the epizootic is apparently not influenced. The
anomaly is accounted for when we remember that the rat and its
parasites are very susceptible to cold and rain. It is then that the
animal seeks a warm, comfortable place from which it does not venture
until driven thence by dire necessity. In other words, the association
of the rat with man is not so intimate in winter, while the reverse is
true of the relation of rat with rat. The rains, while interrupting
the overground migrations and domiciliary visits of rats, drive them
to overcrowded burrows and harboring places. Another factor should be
mentioned in this connection. Human fleas (_P. irritans_), and
probably rat fleas also, are markedly reduced in numbers at that
season of the year. We must conclude, therefore, that the seasonal
prevalence of plague in man is due to the effect of climatic
conditions upon the habits of rats and the life history of the insect
carriers of the bacilli.
An examination of the foregoing should convince everyone that all
former theories as to the prolonged viability of _B. pestis_ in
contaminated soil or in polluted streams, and of the periodical spread
of the infection therefrom, are no longer tenable. It may also be
stated that insanitary conditions, except in so far as they furnish
food and shelter to rats and other vermin, play no important rôle in
the continuance of plague. This general revision has also eliminated
overcrowding as an important factor. In the absence pneumonic cases,
and of suctorial insects, this _bête noire_ of the sanitarian may be
disregarded.
THE OCCURRENCE OF PLAGUE IN THE MARMOT OF ASIA AND THE GROUND SQUIRREL
OF CALIFORNIA.
Rudenko (1900) first pointed out the possibility of contagion by the
“Tarbagan,” a species of the _arctomyinæ_ found in Siberia. He
observed a connection in 1894 between this rodent and an outbreak of
plague in a Cossack family of Soktuewsk. According to Beliatsky and
Zabolotny, each having been an observer in the same field, the natives
of Siberia and Mongolia often acquire plague in this manner. Le Dantec
and other writers have called attention to the probable susceptibility
of the marmot (_Arctomys bobac_), a hibernating rodent of India and
China. The marmot of Thibet, in the opinion of this writer, is the
natural animal host and purveyor of the virus. The literature of the
subject presents no bacteriological evidence, however, of such a
relationship, and plague in the _arctomyinæ_ of Asia is merely an
hypothesis. There is positive evidence though of the susceptibility of
the tree squirrel (_Sciurinæ_) to plague infection. Dr. Alice Corthorn
(1898) reported the finding of a plague-infected squirrel in one of
the outbreaks in the Bombay Presidency.
PLAGUE INFECTION IN GROUND SQUIRRELS.[AF]
Footnote AF:
Genus Citellus, Oken; subgenus Otospermophilus. “California
Mammals,” Frank Stephens.
The demonstration of natural plague in the California ground squirrel
(_Otospermophilus beecheyi_) is perhaps the most important observation
of the antiplague work of the service in 1908. The existence of a
plague epizootic in Contra Costa County was suspected as early as the
summer of 1903, and efforts were made at that time to collect sick and
dead rodents for bacteriological examination. In August (1903) two
fatal cases of human infection occurred in widely separated sections
of the county. The investigation which followed failed to connect
either with a previous case of human plague, but showed an association
with ground squirrels. These deaths occurred during a fatal epizootic
among ground squirrels and suggested a connection which unfortunately
was not confirmed.
None of the circumstances were forgotten, however, and in the second
campaign, begun in September, 1907, in San Francisco, inspectors were
detailed to examine all persons dying in the area under suspicion. No
plague was reported that autumn and winter. Fatal cases occurred and
were reported by the inspectors in July, 1908, as follows: A boy (J.
F.) died July 15, near Concord, and a young woman (M. P.) died July
28, on a ranch 10 miles from Martinez. The two were not associated. An
investigation was ordered at once and a force of trappers was hurried
to the scene with instructions to collect squirrels from the ranches
in the vicinity. The first plague-infected squirrel was found August 5
on the ranch where the boy had died July 15. Of 425 squirrels
collected from August 1 to October 12, 4 showed the gross and
microscopic lesions of natural plague.
A lad (F. M.) sickened August 5, 1908, in Los Angeles, Cal., after
being bitten by a sick ground squirrel. A polyadenitis, which
afterwards proved to be plague, developed in a few days. A dead
squirrel was found nearby and pathological specimens taken from it
were sent to the United States Plague Laboratory in San Francisco.
McCoy recovered _B. pestis_ from the tissue of the animal. This was
the only case of plague reported in Los Angeles. In order to complete
the list of those who contracted plague in the country, two other
cases should be mentioned. F. S., a pregnant woman, died of
bubosepticæmic plague near Concord, Cal., February 29, 1904. The _B.
pestis_ was recovered in pure culture from the axillary glands. In
April, 1906, a school boy of east Oakland developed a multiple plague
adenitis. Investigation showed that he had shot and handled ground
squirrels in the country four or five days before his illness.
THE NATURAL HABITAT OF PLAGUE.
The location of the natural habitat of plague has concerned
sanitarians for many years. Not a few have settled upon India as the
endemic center, while others associate China with the epidemics which
have devastated Europe from remote times. Le Dantec, a recent writer,
suggests the “lofty mountains” between India, Thibet, and China as the
exact location, and selects the rodent (marmot) of that region as the
natural enzootic host.
A panzootic leaves in its wake enzootics of plague in various
countries which persist until the rodents upon which they thrive are
either exterminated or rendered immune. At varying intervals epidemics
spring from them and finally cease with the exhaustion or destruction
of the enzootic foci. Plague disappears in time from these temporary
abodes and retires to its original habitat in India or China.