Chapter 57

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.

The life of the cattle tick is thus spent largely on cattle, and although the young, or larvÊ may live for a long time on the ground in the summer season, they can not mature except as parasites on cattle and horses. We have purposely omitted various details of the life history, including that of the male, as they are not necessary to an understanding of our present subject--Texas fever. How this is transmitted we will proceed to consider. Before the enforcement of the Federal quarantine southern cattle sent north during the spring and summer months carried on their bodies large numbers of the cattle ticks, which, when matured, would drop off and lay their eggs in the northern pastures. After hatching, the young ticks would soon get upon any northern cattle which happened to be on the pasture. So soon as they attached themselves to the skin they inoculated the cattle, and Texas fever would break out a week or more thereafter. For many years there had been a growing suspicion that the cattle tick was in some way concerned in the spread of Texas fever, and the facts which supported this supposition finally became so numerous and convincing that a series of experiments was inaugurated by the Bureau of Animal Industry which served to show that the tick is abundantly able to carry the disease to a herd of healthy cattle, and, in fact, is probably the only agent concerned in the transmission of the disease from southern cattle to susceptible northern animals.

_Injurious effects of cattle ticks._--Unfortunately many cattle owners who have always been accustomed to see both ticks and ticky cattle on their farms are not inclined to attach much importance to these parasites, and, as a rule, through lack of appreciation of their damaging effects, placidly consider them as of little consequence. That ticks may be detrimental to their hosts in several ways has probably not suggested itself to these stockmen, who are most vitally affected, and it therefore seems necessary to emphasize the fact that, in addition to their relation to Texas fever, they may also be injurious to cattle as external parasites. While the power of transmitting Texas fever is undoubtedly the most dangerous property possessed by the cattle tick and is the principal cause for adopting stringent measures looking to its complete eradication, nevertheless there still remain other good reasons for the accomplishment of this achievement. These secondary objections to the presence of ticks on cattle consists in the physical harm they do to the host aside from the production of the specific disease of Texas fever. True, a few parasites may remain on cattle indefinitely without causing any noticeable effect, but it is not uncommon to notice bovine animals on pastures with their hides heavily infested with these pests. In such cases it can readily be seen that the continuous sucking of blood causes more or less impoverishment of the circulation. The animal must therefore be fed more in order to meet the demands of the parasites in addition to the ordinary needs of the host. If the ticks are removed from the body, the bites inflicted are often distinguished by small, inflamed or reddened areas somewhat swollen, with perforations of the skin which may allow the entrance of various kinds of disease germs, and showing that more or less irritation of the hide is produced by these parasites. This condition, together with the loss of blood, frequently induces an irritable state and evidence of uneasiness commonly known as "tick worry," which results in the loss of energy and other derangements of the animal's health. It may in some cases, especially in hot weather, become so pronounced that the animal will lose flesh in spite of good pasturing, thereby reducing the vitality and rendering it more susceptible to the inroads of disease. Moreover, if the infestation of ticks is not controlled, the cattle may be so reduced in condition that growth is retarded, and, in the case of young animals, they may never become fully developed, but remain thin, weak, and stunted--a condition that has been termed "tick poverty"--and easily succumb to other diseases as a result of lowered vitality. In milch cows this debilitating influence of the numerous ticks is shown in a greatly reduced milk supply. This should not appear strange when it is considered that some animals harbor several thousand of the bloodsucking parasites. If these parasites are crushed, it will be found that their intestines are completely filled with a dark, thick mass of blood abstracted from the animal host and containing nutriment that should go to the formation of milk, flesh, and the laying on of fat. In some rare cases the large number of bites on a limited area of skin may be followed by infection with pus-producing organisms, giving rise to small abscesses which may terminate in ulcers. The discharge from these sores, or in some cases the mere oozing of blood serum through the incision made by the mouth parts of the ticks, keeps the hair moist and matted together, and the laying and hatching of fly eggs in these areas give rise to infestation with destructive maggots, causing ulcers and other complications that require medical treatment. These statements regarding the secondary injurious effects of cattle ticks also apply to those ticks which have been previously spoken of as harmless so far as Texas fever is concerned, and, in fact, to all external parasites. Therefore, it is just as important to eradicate the cattle ticks for reasons other than those associated with Texas fever as it is to exterminate lice, fleas, and other vermin. Furthermore, cattle ticks, aside from the losses sustained by their purely parasitic effects, are the greatest menace to the profitable raising and feeding of cattle in the South, because they are an obstacle to cattle traffic between the infected and noninfected districts.

_Loss occasioned by cattle ticks._--The economic aspect of the tick problem is unquestionably of the greatest practical interest, since the fundamental importance of all the other questions which surround it depends upon the actual money value involved. A careful and conservative estimate made in 1916 placed the annual loss caused by the ticks in the United States at $40,000,000, and indicated that the ticks also lowered the assets of the South by an additional $33,000,000. The principal items in these losses are set forth below.

It is well known that those animals coming from an infected district and sold in the "southern pens" of northern stockyards bring about one-half a cent less per pound than the quoted market price. The handicap that is placed on the southern cattle raiser as a result of this decrease in value of his stock will average at this figure $3 per head, allowing an individual weight of 600 pounds for all classes of animals. This decreased value reacts and fixes the valuation of all cattle which remain in the infected territory, thereby reducing the assets of the cattle industry of that section. In addition there is a very great loss from the decrease in flesh and lack of development of southern cattle occasioned by the parasitic life of the ticks from without and by the blood-destroying and enervating properties of the protozoan parasites from within.

The presence of the tick among the cattle of the South not only lessens the value of the cattle on the hoof but causes the gradings of hides that have been infested with ticks as No. 4 quality. The same hide, if free from tick marks, would grade No. 2. The difference in price between these two grades of hides is 3 cents a pound. As the hide of a southern steer weighs about 42 pounds, the presence of the tick in the hide causes a loss in the hide alone of more than $1.26 a hide. It has been shown that the cost of tick eradication is only about 50 cents a head, so that if the counties make a systematic campaign to eradicate the tick, the increase in value of the hide alone would pay for the cost of tick eradication and leave the farmer a net profit of about 76 cents a hide.

The shrinkage in the milk production of cattle harboring many ticks will average 1 quart a day, which in the aggregate is a heavy loss. The damage resulting to the southern purchaser of northern purebred or high-grade cattle is another item of no small moment. About 10 per cent of all such cattle taken into the South die of Texas fever, even after they are immunized by blood inoculations, and about 60 per cent of them succumb to Texas fever when not so treated. As they are usually very expensive animals and of a highly valued strain of blood, the loss in certain cases is excessive and in others almost irreparable, owing to the possible extinction of some particular type especially selected for the improvement of the herd.

Another instance in which it is difficult to figure the injury done by the ticks is in the case of death of nonimmune cattle in the tick-free pastures of the South. Such animals are as susceptible to Texas fever as nonimmune northern cattle, and inasmuch as there is in many States only one out of every four farms infested with ticks, the cattle on the remaining farms will in many cases contract Texas fever when exposed to the fever tick. These losses can scarcely be computed, as the death rate depends so much on the season of the year when exposure occurs and on the age of the animal affected. However, the deaths among such cattle are considerable, although this fact is little appreciated or understood by many outside the infected area.

On rare occasions a small outbreak of Texas fever occurs north of the quarantine line as a result of improperly disinfected cars, of unscrupulous dealers breaking the quarantine regulations, or of some accidental condition. Such damage, however, is slight, but should be considered in summing up the loss occasioned by the fever tick.

The advertisement which a breeder obtains and the sales which are made by having his stock in the show ring are usually lost to the cattle raiser in the infected area who aspires to display his animals in the North, as they are barred from most of these exhibitions. On the other hand, the southern farmer is not given an opportunity to see and be stimulated by the fine specimens of northern cattle which might be shown at southern stock exhibits, for the reason that the danger of contracting Texas fever is too patent to warrant such exposure. A heavy expense is incurred by the Government and the States in enforcing the regulations that apply to the quarantine line.

Another loss which is indirectly sustained by the southern cattle industry through increased freight rates is the cost, to the railroad companies, of cleaning and disinfecting the cars that carry cattle and in providing separate pens for them at various places.

These statements are sufficient to indicate that the loss to the quarantined section from the cattle tick is something enormous. Such a series of encumbrances as those recorded could be carried by the cattle industry of no other section of the country than the South, whose excellent pastures, rich soil, and salubrious climate are the only reasons for its ability to overcome such obstacles in meeting the competition of the West; and it is the inherent capacity of the South for greatly increasing its herds and enlarging its pasture lands that makes the actual loss even secondary to the potential loss from restrictions necessitated by the presence of the cattle tick. This potential loss may be described as the difference between the value of the cattle industry of the South to-day and the extent to which this industry would be increased if farmers and ranchmen were assured that their lands and cattle would not become infested with fever ticks. Could this assurance be given, the beneficial effects would extend over the entire country, because the market of the northern breeder would thereby become greatly extended.

These appalling losses and annual sacrifices of the cattle raisers of the infected district can be entirely effaced, and this at a small proportionate cost; for, with enthusiastic stockmen, satisfactory State legislation, sufficient money, and a corps of trained inspectors, the cattle tick may be exterminated, and every dollar expended in this work will be returned many times during each succeeding year.

_The so-called period of incubation._--After the young ticks have attached themselves to cattle the fever appears about 10 days thereafter in midsummer. When the weather is cool, as in autumn, this period may be a little longer. The actual period of incubation may be shorter, for if blood from a case of Texas fever is injected into the blood vessels of healthy cattle the fever may appear within five days. When cattle graze upon pastures over which southern cattle have passed, the time when the disease appears varies within wide limits. When the animals have been put upon pastures immediately after southern cattle have infected them with ticks, it may take from 30 to 60 days, or even longer, before the disease appears. This will be readily understood when we recall the life history of ticks. The southern cattle leave only matured ticks which have dropped from them. These must lay their eggs and the latter must be hatched before any ticks can get upon native cattle. The shortest period is thus not less than 30 days if we include 10 days for the period of incubation after the young ticks have attached themselves to native cattle. When the infection of pastures with ticks has taken place early in the season, or when it is cold, the period is much longer, because it takes longer for the eggs to hatch.

If native cattle are placed upon pastures which have been infected with ticks some time before, the disease will appear so much sooner, because the young ticks may be already hatched and attack the cattle at once. It will be evident, therefore, that the length of time between the exposure of native cattle on infected fields and the appearance of the disease depends on the date of original infection, and on the weather, whether cold or hot. When native cattle are placed upon fields on which young ticks are already present, they will show the fever in 13 to 15 days if the season is hot.

The fever appears before the ticks have matured. In fact, they are still small enough to be overlooked. In any case very careful search should be made for them in those places which they prefer--the thighs, escutcheon, and udder. After the acute stage of the fever has passed the ticks begin to swell up and show very plainly. (Pl. XLVI, figs. 6 and 7.)

_Prevention._--It is generally accepted that if southern cattle are entirely free from that species of tick known as _Margaropus annulatus_ they can be allowed to mingle with the most susceptible animals without danger. Furthermore, it has been learned from the study of the life history of the cattle tick and by observation that this tick infests pastures only transiently, never permanently, and will not mature except upon cattle or equines, that its extermination is possible, and that the disease it causes may be prevented. Therefore the various methods with these results in view should be directed toward the destruction of ticks on cattle as well as their eradication from the pastures.

METHODS OF ERADICATING THE TICKS.[7]

In undertaking measures for eradicating the tick it is evident that the pest may be attacked in two locations, namely, on the pasture and on the cattle.

In freeing pastures the method followed may be either a direct or an indirect one. The former consists in excluding all cattle, horses, and mules from pastures until all the ticks have died from starvation. The latter consists in permitting the cattle and other animals to continue on the infested pasture and treating them at regular intervals with agents destructive to ticks and thus preventing engorged females from dropping and reinfesting the pasture. The larvÊ on the pasture, or those which hatch from eggs laid by females already there, will all eventually meet death. Such of these as get upon the cattle from time to time will be destroyed by the treatment, while those which fail to find a host will starve in the pasture.