Part 84

11. Ovipositing usually occupies about a week, while hatching varies with the temperature from two to six weeks.

12. Cases can be adduced in which native cattle followed, on the same pasture, the tick-bearing infecting cattle, and remained for a week or more, and yet escaped, the larvæ being as yet unhatched from the ova. Other native cattle, following these two or three weeks later, perished almost without exception.

13. This delay in the hatching may be indefinitely prolonged, and thus in the southern states, the winter may be tided over, without the loss of vitality in the ova, especially if it is covered by leaves, moss, wood, or decaying vegetable matter.

14. When dealing with lung plague in Chicago in 1888, I noted the facts that every cow that entered a city stable through the stock yards during the dry, hot, midsummer weather died of Texas fever within a month, while those that passed through the same yards during a particular rainy week, all escaped. Berkau has shown that, in the absence of the coating of the glutinous saliva, the eggs do not hatch, and here we may assume that this covering was washed off by the rains and the eggs perished.

15. It has long been noticed that the ticks are scarcely at all dangerous to young calves living on milk. This applies not only to calves born of cows native to infected localities, and therefore possibly having a congenital immunity, but also to the calves of northern and susceptible cows, and which were exposed simultaneously with their dams. It suggests a special defensive power in even the bovine system when sustained on animal food. In the Bureau of Animal Industry experiments, calves of four months, already using vegetable food freely, sickened but still, as a rule, recovered.

16. The Bureau fed three cattle with adult live ticks (2000 to one animal) but no infection resulted.

17. Four cattle were injected intravenously with the liquid charged by crushing ticks in a mortar with distilled water. In some cases the liquid was put through a Pasteur filter, in others only through two thicknesses of filter paper. No infection ensued.

18. Lignieres injected, subcutem, in different animals the pulp of the ticks at all stages of life, ground in a mortar with distilled water, but found in no case tristeza as the result nor any destruction of red globules.

The apparent paradox involved in the last three items probably finds its explanation in the statement of Nicolle and Adil-Bey that, in biting, the tick instils into the wound a venomous saliva which causes local congestion and infiltration and presumably operates on the blood globules as well. Curtice describes the two racemose glands situated under the head shield, the secretions of which are pressed out by the movements of the mouth ring and appendages. How much of this irritant and toxic action is inherent in the saliva, and how much due to the protozoan contained in it, has not been shown. Nicolle, Adil-Bey and, later, Lignieres showed a similar toxic property in the blood. Three to five cc. of blood taken from an acute case at the crisis and injected into the marginal vein of the ear in a rabbit, killed the subject in a few seconds. A similar amount thrown into the peritoneum of a Guinea pig destroyed life in a few minutes. It is probable that the dilution of the venom in the mass of tick pulp and distilled water reduced its toxic quality to such a low ebb that the red globules were comparatively unaffected by it and successfully resisted the attacks of the microbe.

The name Boöphilus bovis was given to the bearer of the Piroplasma by Cooper Curtice who made a special study of the tick, and its development. For the description see Parasites, Ixodes. Among the most marked and distinctive features of the female are the extreme shortness and relative breadth of the rostrum, the slender palpi, the eight rows of spines on the lower surface of the labium, the smooth mandibles with terminal hooks, the limbs long, slender, in seven segments, and each furnished with a terminal pad (pulvillus) and one hook (fore limbs) or two hooks (hind). Curtice has identified the ticks of hæmoglobinuria in various other countries with the boöphilus. The Garrapata of Mexico and the West Indies, the Hæmaphysalis rosea of Cuba (Koch), the Ixodes Annulata of Florida (Say), the Ixodes Dugesii of Italy (Nequin), the Ixodes Algeriensis and the Ixodes Egypti he found to be identical. There may be some doubt as to the Rhipicephalus Annulatus Microplus of Buenos Ayres, but as it agrees with the boöphilus in size, in the thickness of its rostrum, in the eight rows of hooks on the lower surface of the labium, in its host and habits, in the fact that it transfers the piroplasma to cattle, and that it prevails on the same continent in what were formerly colonies of Spain it is in all probability the same tick. Curtice holds that it was originally a North African tick, which was carried by the Spaniards to their American colonies. The Rhipicephalus Annulatus of Roumania is probably the same, together with the ticks that convey the Piroplasma in the other countries of Europe. There remain the Hæmaphysalis of South Africa and the “Scrub-tick” of Australia to be identified with, or differentiated from the Boöphilus. The life history of the Queensland “scrub” tick coincides with that of the boöphilus of America (Pound). As Australia derived her cattle from Britain it is improbable that the tick was imported from Europe.

Lesions. If the course of the disease has been short, followed by an early death, the carcass may be full and rounded, but if the animal has been sick for five or six days there is marked loss of condition and weight—emaciation. As after any other affection occurring during very hot weather, decomposition sets in early, though not quite so speedily as in anthrax, in which the subject dies full of rich blood. Something, too, depends on the condition at death, putrefaction being manifestly slower in protracted and debilitated cases. The color of the skin, the mucosæ and normally white tissues varies in the same way. As it has been largely seen in our northern States (and Australia) in fat cattle, which contracted the disease in railway cars, cattle markets, or dealers’ or butchers’ parks, etc., the deep orange hue of the white tissues is one of the most marked features, and even the muscles have a deep mahogany yellow hue. In poor milch cows and stock cattle in the South, on the other hand, the icteric hue is often conspicuous by its absence. Cattle killed early for experimental purposes may also show less icterus. The color appears to be influenced largely by the abundance of red globules in the blood when the animal was attacked, by the rapid destruction of these globules, and the saturation of the blood and tissues with hæmoglobin in solution. The presence of ticks on the skin, especially along the ventral aspect, inside of the thighs, on the scrotum, udder or perineum, sufficiently explains the number of minute infiltrations into the derma, the oozing of blood or serum, and the matting of the hairs into little tufts.

The pale, watery condition of the blood was recognized as one of the most constant features in 1868, together with the disappearance of the red globules. The clot is remarkably soft and, at the crisis of the disease, the serum is of a reddish hue by reason of the hæmoglobin in solution. When, however, the urine is no longer stained, the hæmoglobin having been eliminated, the serum assumes its normal pale amber hue. For the first counting of the red globules in this disease we are indebted to the Bureau of Animal Industry. The average count in healthy cattle approximated to 6,000,000 per mm. of blood, and in three days this would descend to 4,000,000, 3,000,000, 2,000,000 or even 1,183,000. The rates of decrease was ⅛ to ⅙ of the entire number in one day. In case of recovery the repair of the red globules was slow, from one to two months being required to bring them up to the normal standard. Lignieres claims recoveries after the count had gone as low as 300,000 per mm., and in fatal cases, a few hours before death, it may be but 31,000 per mm.

In high conditioned animals, with high fever often aggravated by travel, the muscles may be dark and firm, but in those out of condition and in the advanced anæmic stages of the disease the muscles are pale, and there may be subcutaneous œdema below the chest and belly. These last features are especially noted by Smith and Kilborne.

The lungs are usually normal. Sometimes limited congestions, punctiform petechiæ, emphysema and small areas of œdema or hepatization are noticed (Smith and Kilborne).

The pericardium contains a little bloody serum and is marked by petechiæ.

The left heart is usually empty, but the right heart full of fluid, or later, of clotted blood, in the latter case without buffy coat. The endocardium, and especially on the musculi papillares, is marked by petechiæ, punctuate or in considerable patches. The cardiac capillaries are full of blood, with numerous piroplasmata.

The peritoneum often contains a little reddish serosity, and a slight gelatinoid exudation is sometimes found around the kidneys or elsewhere in the abdomen. Petechiæ are frequent.

The stomachs usually show petechiated spots on the mucous membranes, and more or less diffuse congestion. Sloughing of the mucosa at such points is not uncommon, and even perforation of the folds of the third and fourth stomachs. The Bureau of Animal Industry and Lignieres both found these stomach lesions very inconsiderable. The smaller pinhead erosions described by Gamgee were identified by the Bureau of Animal Industry as bites of the strongylus convolutus. The small intestines are usually moderately congested.

The cæcum and colon show more congestion, becoming at times of a deep red or almost black hue, and considerable extravasation of blood may take place. This is especially marked in the rectum, which may be of a port wine hue, comparable to that seen in rinderpest or hæmorrhoidal anthrax. The fæces are often dry and massed in balls in cæcum and rectum, while if diarrhœa has set in, the discharges may be colored with blood or blood elements. Yet in the cases reported by the Bureau serious lesions of the intestines were rather the exception, and some subjects showed scarcely any lesion.

The liver is usually enlarged, averaging three to five pounds heavier than in a healthy ox of the same weight. In these enlarged and congested cases it is of a deep yellowish brown color, and often shows yellow spots on the darker ground. Microscopically each acinus has a bright yellow centre from which yellow radiating canals diverge to join the peripheral gall duct. In the superficial or portal portion of the acinus, the hepatic cells are granular from fatty change, yet the nucleus is usually still recognizable. Toward the central zone it may have disappeared. The further this has advanced, the softer, the more easily pitted and the more friable the liver. The congestion of these radical gall ducts with the dense colored bile, displays the structure of the acini in a clear and beautiful way, which no injection can accomplish. When the affected tissue is teased out and placed under the microscope the inspissated contents of the bile canaliculi may be seen as yellow cylindroid casts sometimes bifurcated to represent the union of the two canals. If stained in Ehrlich’s acid hæmatoxylin, the necrotic elements refuse to take the stain so that the contrast between the dead and the living tissues is enhanced. Fatty degeneration is common in the liver of healthy beef cattle so that this is less significant than the congestion of the acini, and the phenomenal distension of the radical gall ducts with inspissated bile.

The gall bladder is usually full (½ pint to 1 quart or more), and its mucous membrane congested and sometimes petechiated. The bile is thick and viscid, like tar, it may be yellowish green, darkening on exposure and contains hæmatoidin crystals and abundance of flocculi showing bright yellow or orange by transmitted light and reddish brown by reflected light.

The spleen is always enlarged, often enormously so. From an average weight of 1.5 lb. to 1.7 lb. for a 1000 lbs. ox, it will rise to 2, 7 or even 10 lbs. One measured 27 inches long by 7½ inches wide and in the centre 3 inches thick (Rauch). Even in apparent health the Gulf coast cattle have spleens averaging about 2½ lbs.

The spleen is gorged with blood which appears purple as seen through the stretched and attenuated capsule, and darker petechial spots are found at intervals. When cut into, the pulp alone appears dark, brownish red, grumous, and showing under the microscope many red blood cells, larger cells granular and undergoing fatty degeneration, yellow flocculi, crystals of hæmatoidin, and granules of black pigment. It is the excess rather than the nature of these agents that is significant. The pulp may be pressed or washed out, bringing the trabeculæ and Malphigian bodies into view.

The kidneys are most seriously affected in acute and rapidly fatal cases. There may be œdema, with blood staining and even extravasation on their lower surface and in the adipose tissue. The gland may be enlarged and the cortical substance congested of a dark brownish red or black. Its capillaries are gorged with red globules in which the piroplasmata are very numerous. The medullary portion is much paler, and with fatty granules in the epithelium, and oil globules in the tubules. The renal pelvis is more or less petechiated and marked by extravasations.

The bladder is marked by petechiæ and usually contains some quarts of urine more or less deeply stained with hæmoglobin. The depth of color is in exact ratio with the extent and rapidity of the destruction of red globules, and of the elimination of their coloring matter. When the destruction is proceeding rapidly the urine may be as dark as port wine; when their disintegration has lessened it may be pale though the temperature is still high (105° F.) In slight and tardy cases there is reason to believe that the redness of the urine may be omitted altogether as is the icteric discoloration of the mucosæ, and hence cases seen in animals indigenous to the protozoan fever districts, have been described as a distinct disease. In these mild cases and advanced stages there is usually a certain amount of albuminuria remaining. In the early stages the urine is strongly alkaline, effervesces with acids, and has a high specific gravity (1030–1040); later when abstinence and suspended digestion and assimilation causes the patient to subsist on its own tissues the reaction may become distinctly acid and the specific gravity reduced (1010–1020). It no longer effervesces. During convalescence while there is a great deficiency of red globules and other blood solids, the urine tends to become pale and watery, of a low specific gravity, and lacking in even its normal pigments.

The womb will at times show petechiæ and in pregnant cows the fœtus will show sero-sanguineous effusions or even extravasations in the chest or abdomen, and hæmoglobinuria (Lignieres).

Incubation. Outbreaks occurring in the North, in herds into which southern infected cattle have been brought, were at first held to indicate an incubation of thirty or forty days (or even sometimes sixty-five), but this is now explained by the time required for the laying and hatching of the eggs of the mature ticks and the evolution of infecting young larval or seed ticks. The actual incubation, as shown by the subcutaneous or intravenous injection of the blood of an infected ox, extends from three to ten days. The hyperthermia is usually shown on the third day, and the more manifest outward symptoms on the sixth. Extreme heat of the weather, a special susceptibility of the animal infected, and especially a large dose of the blood and protozoa will hasten somewhat the onset, but three to six days may be set down as the rule after the ticks have introduced the parasite into their victim. Cattle taken from the northern states and placed on southern pastures, or passing over trails already well stocked with the ticks, are infected at once and sicken in from three to ten days. Cattle in their northern home placed on a previously uninfested field with southern cattle just arrived, do not suffer for thirty, forty, sixty, and in exceptional cases, even ninety days. The paradox is explained by the time wanted for the laying of the eggs and the hatching of the tick larvæ. The female tick does not lay eggs until she is fully mature, and if the ticks on a southern ox are still immature there is a variable period of delay until the eggs are mature enough to be deposited. Then the ovigerous tick drops off her host and spends one week in laying her eggs. In warm weather these eggs take three to four weeks to hatch, so that usually five weeks elapse before the young (seed ticks) can climb upon the ox and infect him. Add three to six days more for the actual incubation and we account for about six weeks of delay in the appearance of the disease in northern cattle. If we consider further that a wet season occurring after the eggs have been laid and before they are hatched tends to divest them of their protective covering and to expose them to destruction, and that, in any case, a cold season will delay the hatching until the recurrence of warm weather, and that the absence of bovine victims will doom the new-born larva to an arrest of development, so that a further indefinite delay may be entailed, we have abundant explanation of the frequently delayed evolution of symptoms. Yet in general terms the apparent prolongation of incubation is due to fortuitous circumstances which delay the infection, and not to any actual extension of the incubation itself.

Symptoms of Acute Type. Cattle infected outside the area of habitual prevalence and stock from noninfected districts, conveyed into the infected ones in hot weather, usually contract the disease in its acute and fatal form. The period of the year is often significant, a number of animals being attacked at once in the hot dry period of late summer or autumn—July to September in North America, February to May in Argentina.