inflammatory disease of domestic and wild animals, resulting from the
introduction of a specific organism into the deep connective tissues of a
susceptible animal and proving fatal in many instances within 24 to 48
hours. The disease may be inoculated from one animal to another, but only
by inserting the virus deeply below the skin. It is infrequently met with
in cattle, but may follow operating wounds, as roweling, castration, and
phlebotomy, which have become infected with septic matter, soil, or unclean
instruments. In the pathological laboratory of the Bureau of Animal
Industry the organism has also been obtained from the infected muscles of a
calf that was supposed to have died of blackleg, and, as a result, all
blackleg virus is thoroughly tested before it is made into blackleg vaccine
in order to exclude the malignant-edema organism. The essential cause of
malignant edema is a long, slender, motile, spore-bearing bacillus,
resembling the bacillus of blackleg, and which can develop only in the
absence of the atmosphere. Unlike the bacilli of anthrax and blackleg,
which are confined to certain districts, this organism is widely
distributed and found in ordinary garden soil, foul water, and in the
normal intestinal tract of the herbivora. It may be brought to the surface
of the soil by growing plants, rains, winds, or burrowing insects and
rodents. In animals that have succumbed to the disease the germ is confined
to the seat of infection, but a few hours after death it may migrate
through the blood channels to other parts of the body. The bacillus may
attack man, horses, asses, goats, sheep, pigs, cats, dogs, and poultry.
Adult cattle, although refractory to experimental inoculation, suffer from
natural infection, while calves are susceptible to both these methods of
exposure. (Kitt.) The introduction of the bacillus into abrasions of the
skin and superficial sores rarely does any harm, because the germ is
quickly destroyed by contact with air. If, however, the organisms are
inserted deeply into the subcutaneous tissues of susceptible animals, they
quickly develop, producing a soluble poison, which is the fatal agent.
In lamb-shearing season, or after docking or castration, the mortality is
higher among these animals because of wounds inflicted at such times. The
application of antiseptics to wounds thus made will reduce the percentage
of deaths to a minimum.
_Symptoms._--Usually the first symptoms are overlooked. In the early stages
the animal appears listless, disinclined to move about, and lies down in
shady and quiet places. If forced to move about, the hind legs are drawn
forward with a peculiar, stiff, dragging movement, and there may be slight
muscular trembling over all the body, which becomes more intense as the
disease progresses. When driven, the animal shows signs of fatigue,
ultimately dropping to the ground completely exhausted. Breathing becomes
fast and painful, with frequent spasmodic jerks.
The pulse is quick and weak and the temperature is 106∞ to 107∞ F. An
edematous, doughy, and painful swelling appears at the point of infection.
This tumefaction spreads more and more, and crackles on pressure. In case
of an open wound, a fetid liquid and frothy discharge is observed. The
center of the swelling may appear soft and jellylike, while the margin is
tense, hot, and painful. The symptoms increase rapidly, resulting in coma
and death.
_Lesions._--After death the fat and subcutaneous tissues surrounding the
infected area are infiltrated with a yellow gelatinous material containing
an orange-colored foam, due to the presence of gas bubbles.
The muscles at this point are friable, spongy, and of a uniform brownish
tint, dissociated by gas and with a blood-tinged exudate. This gangrenous
tissue, when present before death, can be removed without pain to the
animal. The intestines are generally normal, but, together with the
peritoneum, they may be inflamed, and the lungs are usually the seat of an
edema. The spleen, liver, and kidneys retain their normal appearance, in
marked contrast with anthrax.
_Differential diagnosis._--Unlike blackleg, this disease never appears as
an epizootic but in isolated cases. It may also be differentiated from the
former by the history of a recent parturition or surgical operation, by the
presence of an external injury at the site of the swelling accompanied with
a fetid liquid discharge, and the gangrenous appearance of the tumefaction.
Man is susceptible to malignant edema, but not to blackleg. Malignant edema
may also be easily differentiated from anthrax in that the blood and spleen
are normal in appearance, while in the latter disease the blood is dark and
of a tarlike consistency, and the spleen appears swollen, injected, and
softened. The local tumor in malignant edema contains gas bubbles, which
are absent in anthrax swellings. Inoculation experiments of guinea pigs,
rabbits, and chickens will also disclose the differences among the
above-mentioned three diseases, since all these species are killed by the
germ of malignant edema, only the first two species by the anthrax
bacillus, while the guinea pig alone will succumb to the blackleg
infection.
_Treatment._--Treatment is chiefly surgical and consists in laying the
infected areas wide open by free incision, followed by a liberal
application of a 30 per cent solution of hydrogen dioxid and subsequently a
5 per cent solution of carbolic acid. Usually the disease when observed has
advanced to such an extent that medicinal interference is without avail.
Preventive treatment is by far the most desirable, and consists,
essentially, in a thorough disinfection of all accidental and surgical
wounds, the cleansing of the skin, and the exclusion of soil, filth, and
bacteria during surgical operations of any nature. Sheds, barns, and
stables should receive a thorough application of quicklime or crude
carbolic acid wash after all rubbish has been removed and burned. All dead
animals should be burned or deeply buried and covered well with quicklime.
SOUTHERN CATTLE FEVER (TEXAS FEVER, TICK FEVER).
[Pls. XLIV-XLIX.]
This disease, which is more commonly known as Texas fever, and sometimes as
splenetic fever, is a specific fever communicated by cattle which have
recently been moved northward from the infected district; it is also
contracted by cattle taken into the infected district from other parts of
the world. It is characterized by the peculiarity among animal diseases
that the animals which disseminate the infection are apparently in good
health, while those which sicken and die from it do not, as a rule, infect
others.
It is accompanied with high fever, greatly enlarged spleen, destruction of
the red blood corpuscles, escape of the coloring matter of the blood
through the kidneys, giving the urine a deep-red color, with a yellowness
of the mucous membranes and fat, which is seen more especially in fat
cattle, by a rapid loss of strength, and with fatal results in a large
proportion of cases.
This disease has various names in different sections of the country where
it frequently appears. It is often called Spanish fever, acclimation fever,
red water, black water, distemper, murrain, dry murrain, yellow murrain,
bloody murrain, Australian tick fever, and tristeza of South America.
The earliest accounts we have of this disease date back to 1814, when it
was stated by Dr. James Mease, before the Philadelphia Society for
Promoting Agriculture, that the cattle from a certain district in South
Carolina so certainly disease all others with which they mix in their
progress to the North that they are prohibited by the people of Virginia
from passing through the State; that these cattle infect others while they
themselves are in perfect health, and that cattle from Europe or the
interior taken to the vicinity of the sea are attacked by a disease that
generally proves fatal. Similar observations have been made in regard to a
district in the southern part of the United States.
The northern limits of this area are changed yearly as a result of the
dissemination or eradication of the cattle tick along the border, but the
infected area has gradually decreased, owing to the successful endeavors
pushed forward to eliminate the ticks.
It was the frequent and severe losses following the driving of cattle from
the infected district in Texas into and across the Western States and
Territories which led to the disease being denominated Texas fever. It is
now known, however, that the infection is not peculiar to Texas or even to
the United States, but that it also exists in southern Europe, Central and
South America, Australia, South Africa, and the West Indies.
When cattle from other sections of the country are taken into the infected
district they contract this disease usually during the first summer, and if
they are adult animals, particularly milch cows or fat cattle, nearly all
die. Calves are much more likely to survive. The disease is one from which
immunity is acquired, and therefore calves which recover are not again
attacked, as a rule, even after they become adult.
When the infection is disseminated beyond the permanently infected
district, the roads, pastures, pens, and other inclosures are dangerous for
susceptible animals until freezing weather. The infection then disappears,
and cattle may be driven over the grounds or kept in the inclosures the
succeeding summer and the disease will not reappear. There are some
exceptions to this rule in the section just north of the boundary line of
the infected district. In this locality the infection sometimes resists the
winters, especially if they are mild.
In regard to the manner in which the disease is communicated, experience
shows that this does not occur by animals coming near or in contact with
one another. It is an indirect infection. The cattle from the infected
district first infect the pastures, roads, pens, cars, etc., whence the
susceptible cattle obtain the virus secondhand. Usually animals do not
contract the disease when separated from infected pastures by a fence. If,
however, there is any drainage or washing by rains across the line of fence
this rule does not hold good.
The investigations made by the Bureau of Animal Industry demonstrate that
the ticks which adhere to cattle from the infected district are the only
known means of conveying the infection to susceptible cattle. The infection
is not spread by the saliva, the urine, or the manure of cattle from the
infected district. In studying the causation and prevention of this
disease, attention must therefore be largely given to the tick, and it now
seems apparent that if cattle could be freed from this parasite when
leaving the infected district they would not be able to spread the malady.
The discovery of the connection of the ticks with the production of the
disease has played a very important part in determining the methods that
should be adopted in preventing its spread. It established an essential
point and indicated many lines of investigation which have yielded and are
still likely to yield very important results.
_Nature of the disease._--Texas fever is caused by an organism which lives
within the red blood corpuscles and breaks them up. It is therefore simply
a blood disease. The organism does not belong to the bacteria but to the
protozoa. It is not, in other words, a microscopic plant, but it belongs to
the lowest forms of the animal kingdom. This very minute organism
multiplies very rapidly in the body of the infected animal, and in acute
cases causes an enormous destruction of red corpuscles in a few days. How
it gets into the red corpuscle it is not possible to state, but it appears
that it enters as an exceedingly minute body, probably endowed with motion,
and only after it has succeeded in entering the corpuscle does it begin to
enlarge. Plate XLV, figure 4, illustrates an early stage of this blood
parasite. The red corpuscle contains a very minute, roundish body which is
stained blue to bring it into view. The body is, as a rule, situated near
the edge of the corpuscle. Figure 5 illustrates an older stage in the
growth of the parasite, in fact the largest which has thus far been
detected. It will be noticed that there are usually two bodies in a
corpuscle. These bodies are in general pear-shaped. The narrow ends are
always toward each other when two are present in the same corpuscle. If we
bear in mind that the average diameter of the red blood corpuscles of
cattle is from 1/4000 to 1/5000 inch, the size of the contained parasite
may be at once appreciated by a glance at the figures referred to.
The various disease processes which go on in Texas fever, and which we may
observe by examining the organs after death, all result from the
destruction of the red corpuscles; this destruction may be extremely rapid
or slow. When it is rapid we have the acute, usually fatal, type of Texas
fever, which is always witnessed in the height of the Texas-fever season,
that is, during the latter weeks of August and the early weeks of
September. When the destruction of corpuscles is slower, a mild, usually
nonfatal, type of the disease is called forth, which is only witnessed late
in autumn or more rarely in July and the early part of August. Cases of the
mild type occurring thus early usually become acute later and terminate
fatally.
The acute disease is fatal in most cases, and the fatality is due not so
much to the loss of blood corpuscles as to the difficulty which the organs
have in getting rid of the waste products arising from this wholesale
destruction. How great this may be a simple calculation will serve to
illustrate. In a steer weighing 1,000 pounds, the blood in its body weighs
about 50 pounds, if we assume that the blood represents one-twentieth of
the weight of the body, which is a rather low estimate. According to
experimental determination at the bureau station, which consists in
counting the number of blood corpuscles in a given quantity of blood from
day to day in such an animal, the corpuscles contained in from 5 to 10
pounds of blood may be destroyed within 24 hours. The remains of these
corpuscles and the coloring matter in them must be either converted into
bile or excreted unchanged. The result of this effort on the part of the
liver causes extensive disease of this organ. The bile secreted by the
liver cells contains so much solid material that it stagnates in the finest
bile canals and chokes these up completely. This in turn interferes with
the nutrition of the liver cells and they undergo fatty degeneration and
perish. The functions of the liver are thereby completely suspended and
death is the result. This enormous destruction of corpuscles takes place to
a large extent in the kidneys, where a great number of corpuscles
containing the parasites are always found in acute cases. This accounts
largely for the blood-colored urine, or red water, which is such a
characteristic feature of Texas fever. The corpuscles themselves are not
found in the urine; it is the red coloring matter, or hemoglobin, which
leaves them when they break up and pass into the urine.
_Symptoms._--After a period of exposure to infected soil, which may vary
from 13 to 90 days, and which will be more fully discussed under the
subject of cattle ticks as bearers of the Texas-fever parasite, the disease
first shows itself in dullness, loss of appetite, and a tendency to leave
the herd and stand or lie down alone. A few days before these symptoms
appear the presence of a high fever may be detected by the clinical
thermometer. The temperature rises from a normal of 101∞ to 103∞ F. to 106∞
and 107∞ F. There seems to be little or no change in temperature until
recovery or death ensues. The period of high temperature or fever varies
considerably. As it indicates the intensity of the disease process going on
within, the higher it is the more rapid the fatal end. When it does not
rise above 104∞ F. the disease is milder and more prolonged.
The bowels are mostly constipated during the fever; toward the end the
feces may become softer and rather deeply tinged with bile. The urine shows
nothing abnormal during the course of the disease until near the fatal
termination, when it may be deeply stained with the coloring matter of the
blood. (Hemoglobinuria; see Pl. XLV, fig. 3.) Although this symptom is
occasionally observed in animals which recover, yet it may generally be
regarded as an indication of approaching death. The pulse and respiration
are usually much more rapid than during health.
Other symptoms in addition to those mentioned have been described by
observers, but they do not seem to be constant, and only those described
above are nearly always present. As the end approaches emaciation becomes
very marked, the blood is very thin and watery, and the closing of any
wound of the skin by clots is retarded. The animal manifests increasing
stupor and may lie down much of the time. Signs of delirium have been
observed in some cases. Death occurs most frequently in the night.
The duration of the disease is very variable. Death may ensue in from three
days to several weeks after the beginning of the fever. Those that recover
ultimately do so very slowly, owing to the great poverty of the blood in
red corpuscles. The flesh is regained but very gradually, and the animal
may be subjected to a second, though mild, attack later on in the autumn,
which pushes the full recovery onward to the beginning of winter.
In the mild type of the disease, which occurs in October and November,
symptoms of disease are well-nigh absent. There is little if any fever, and
if it were not for loss of flesh and more or less dullness the disease may
pass unnoticed, as it undoubtedly does in a majority of cases. If, however,
the blood corpuscles are counted from time to time a gradually diminishing
number will be found, and after several weeks only about one-fifth or
one-sixth of the normal number are present. It is indeed surprising how little
impression upon the animal this very impoverished condition of the blood
appears to make. It is probable, however, that if two animals kept under
the same conditions, one healthy and the other at the end of one of these
mild attacks, are weighed, the difference would be plainly shown.
_Pathological changes observable after death._--In the preceding pages some
of these have already been referred to in describing the nature of the
disease. It is very important at times to determine whether a certain
disease is Texas fever or some other disease, like anthrax, for example.
This fact can, as a rule, be determined at once by a thorough microscopic
examination of the blood. The necessary apparatus and the requisite
qualifications for this task leave this method entirely in the hands of
experts. There are, however, a considerable number of changes caused by
this disease which may be detected by the naked eye when the body has been
opened. Put together they make a mistake quite impossible. The presence of
small ticks on the skin of the escutcheon, the thighs, and the udder is a
very important sign in herds north of the Texas-fever line, as it indicates
that they have been brought in some manner from the South and have carried
the disease with them, as will be explained later. Another very important
sign is the thin, watery condition of the blood, either just before death
or when the fever has been present for four or five days. A little incision
into the skin will enable any one to determine this point. Frequently the
skin is so poor in blood that it may require several incisions to draw a
drop or more.
The changes in the internal organs, as found on post-mortem examinations,
are briefly as follows: The spleen, or milt, is much larger than in healthy
animals. It may weigh three or four times as much. When it is incised the
contents or pulp is blackish (see Pl. XLIV, fig. 1), and may even well out
as a disintegrated mass. The markings of the healthy spleen (fig. 2) are
all effaced by the enormous number of blood corpuscles which have collected
in it, and to which the enlargement is attributable. Next to the spleen the
liver will arouse our attention. (See Pl. XLV, fig. 2.) It is larger than
in the healthy state, has lost its natural brownish color (fig. 1), and now
has on the surface a paler, yellowish hue. When it is incised this
yellowish tinge, or mahogany color, as it has been called by some, is still
more prominent. This is owing to the large quantity of bile in the finest
bile capillaries, and as these are not uniformly filled with it the cut
surface has a more or less mottled appearance. This bile injection causes
in many cases a fatty degeneration of the liver cells, which makes the
organ appear still lighter in color.
In all cases the gall bladder should be examined. This is distended with
bile, which holds in suspension a large number of yellow flakes, so that
when it is poured into a tall bottle to settle fully one-half or more of
the column of fluid will be occupied by a layer of flakes. If mucus is
present at the same time, the bile may become so viscid that when it is
poured from one glass to another it forms long bands. The bile in health is
a limpid fluid, containing no solid particles.
If the animal during life has not been observed to pass urine colored with
blood or red water, the bladder should be opened. This quite invariably, in
acute cases, contains urine which varies in color from a deep port wine to
a light claret. In many cases the color is so dense that light will not
pass through even a thin layer. (Pl. XLV, fig. 3.) The kidneys are always
found congested in the acute attack. The disease exerts but little effect
on the stomach and intestines beyond more or less reddening of the mucous
membrane; hence an examination of them may be safely omitted. The lungs
are, as a rule, not diseased. The heart usually shows patches of blood
extravasation on the inside (left ventricle) and less markedly on the outer
surface.
We have observed jaundice of the various tissues but very rarely. It has
been observed by some quite regularly, however.
During the hot season about 90 per cent of the susceptible mature animals
from a noninfected district die, but later, in the cool weather, the
disease assumes a milder type, with a consequent decrease in the number of
deaths.
_The cattle tick, Margaropus annulatus, as the carrier of Texas fever._
(Pls. XLVI, XLVII, and XLVIII.)--The cattle tick is, as its name indicates,
a parasite of cattle in the southern part of the United States. It belongs
to the group of Arthropoda and to the genus _Margaropus_ (or _Boophilus_),
which is included in the order Acarina. Its life history is quite simple
and easily traced from one generation to another. It is essentially a
parasite, attaching itself to the skin (Pl. XLVIII) and drawing the blood
of its host. It is unable to come to maturity and reproduce its kind unless
it becomes attached to the skin of cattle, whence it may obtain its food.
The eggs laid on the ground after the female has dropped from the host
begin to develop at once. When the embryo is fully formed within the shell
it ruptures this and gains its freedom. The time required from the laying
of the eggs to their hatching varies considerably, according to the
temperature. In the laboratory in the heat of midsummer this was
accomplished in about 13 days. In the late fall, under the same conditions,
it required from four to six weeks. The larva after emerging from the egg
is very minute, six-legged, and is just visible to the naked eye. (Pl.
XLVI, fig. 3.) If these larvÊ are kept on a layer of moist sand or earth in
a covered dish, they may remain alive for months, but there is no
appreciable increase in size. So soon, however, as they are placed upon
cattle growth begins.
On pastures these little creatures soon find their way on to cattle. They
attach themselves by preference to the tender skin on the escutcheon, the
inside of the thighs, and on the base of the udder. Yet when they are very
numerous they may be found in small numbers on various parts of the body,
such as the neck, the chest, and the ears. (Pl. XLVIII and Pl. XLIX, fig.
1.)
The changes which they undergo during their parasitic existence were first
studied by Dr. Cooper Curtice, of the Bureau of Animal Industry, in 1889.
The young tick molts within a week, and the second or nymphal stage of the
parasite's life is thus ushered in. After this change it has four pairs of
legs. Within another week another molt takes place by which the tick passes
from the nymphal to the sexual, or adult, stage. Impregnation now takes
place, and, with the development of the ova in the body, the tick takes an
increased quantity of blood, so that in a few days it becomes very much
larger. That the rapid growth is due to the blood taken in may be easily
proved by crushing one. The intestine is distended with a thick, tarry mass
composed of partly digested blood. When the female has reached a certain
stage of maturity she drops to the ground and begins to lay a large number
of eggs, which hatch in the time given above.