Part 51

The rational conclusion is, that while there is every indication of a primal identity of the two diseases, and indeed of all forms of variola, as shown by a disposition of the virus from one genus, when inoculated upon a totally different genus, to show some indication of the characteristic eruption of the latter, yet the generic type, which comes from the long continued growth in the one class of animal, becomes so fixed, that it cannot be overcome at once, and sometimes apparently not at all, by transferring it to an animal of another class.

If the unfortunate results obtained by Martin, Reiter, and Chauveau, are insufficient to deter from the use of smallpox lymph which has been passed through the cow, the long experience with humanized vaccine, which in its inoculation from man to man for a century has shown no tendency to revert to smallpox virus should be a sufficient warning against such dangerous optimism.

No deduction can be safely drawn from the comparative mildness of most of the cases caused by reinoculation from cow or horse to man, inasmuch as that all forms of variola can be rendered less severe by resorting to inoculation, which was extensively practised to limit the ravages of smallpox before the days of vaccination, and is still largely resorted to in the case of sheeppox in Europe. In each of these diseases the mortality can easily be reduced to 2 per cent. instead of the 20 to 50 per cent. which are lost when the disease is contracted casually.

As occurring casually, cowpox like horsepox is rare. Yet in Denmark, a dairying country, 1,037 cases were reported in 1877–8, and 878 cases in 1888–9. I have found some outbreaks explainable, through the existence of vaccinations in the families of the milkers, and Bollinger says that in Germany, most outbreaks take place in spring, the time when children are vaccinated. He should have added that this is the usual time of parturition in the cow, the time when primipara are first subjected to the danger from the hands of the milker, and when the cow from the noninfected district is brought into an infected stable for the season’s milking. In a dairying district in Tompkins Co., N.Y., the affection appeared every spring, in the same barns, in heifers with their first calf and in newly bought cows. All older cows, bulls, steers and unimpregnated heifers escaped.

Symptoms. The period of incubation is two days, after inoculation, and though it may appear to extend to a week when the disease is contracted accidently, it is impossible in such cases to state the exact date of infection. The preliminary fever is not always present, or recognized, yet there may be slight encrease of temperature, partial impairment of appetite and rumination, extra firmness of the fæces, a higher color of the urine, and above all a slight diminution of milk, which is a little more watery and coagulates more readily, than the normal.

This is followed by heat and tenderness of the udder and the appearance on the teats of small, pale red nodules the size of a pea or larger. In one or two days more the nodule, largely encreased in size, presents in the centre a depressed or umbilicated bluish white portion, with a firm yellowish, reddish or reddish blue margin, and outside this a soft pink areola, shading off into the white skin. The epidermis is raised at points by a viscid, yellowish lymph, enclosed in a series of saccules (multilocular vesicle). The vesicle encreases to 8 or 10 lines in diameter by the eighth or tenth day, and exceptionally, the umbilication is effaced by the excessive production of lymph. If left unbroken a brownish shade appears in the centre and gradually extends toward the periphery, the contents becoming purulent, and the pustule gradually drying up to form a crust. The drying and thickening of the crust goes on until the fourteenth day and the crust is usually detached by the twentieth, leaving a pale rose colored, smooth, shallow depression, which forms the permanent pit left after the skin has healed. The primary scabs usually show the central umbilication, and always the conical projection in the center of the deep aspect, and corresponding to the pit.

Vesicles on the mammæ may pass through the above stages, but those on the teats are usually ruptured by the hands of the milker as soon as the liquid is thrown out, and this gives rise to troublesome sores, with complex infections, at times implicating the gland tissue so as to cause destructive mammitis with loss of one or more quarters, and in any case abraded and irritated at each milking, so that the animal resists handling, the milk is drawn off imperfectly, and dries up or the cow becomes an inveterate kicker. If the milker has not been vaccinated he is liable to contract the disease.

A succession of vesicles often appear on the same animal, so that they may be found in all different stages of vesicle, pustule and crust on the same bag at one time. The later eruptions may be the result of inoculation from the earlier ones, and tend to prolong the attack materially.

In inoculation of the bovine animal for the production of lymph for vaccination, the skin of the abdomen from the symphysis pubis to the umbilicus is shaved, or in other cases the skin between the thighs, or in still others the skin on each side over the loins, and the virus applied in 50 to 200 points, by preference scraped until liquid oozes, but without any escape of blood. In a warm room the eruption matures in four or five days, its form taking on an appearance approximating that seen on the hairy skin of the horse. The individual lesions are somewhat extended corresponding in form and size to the abrasion on which the lymph was applied, and usually present the appearance of a raised patch, covered by a grayish film of epidermis, on the removal of which there is seen a raw alveolated surface filled with the amber-colored lymph.

Differential Diagnosis. From aphthous fever, cowpox is clearly distinguished by (a) the multilocular structure of the vesicle, while that of aphthous fever is a single undivided cavity which can be drained completely by a single needle prick; (b) by the pitting or umbilication, the aphthous vesicle being uniformly rounded and convex; (c) by the absence of vesicles or sores on the mouth and feet, which are rarely wanting in the aphthous eruption; (d) by the comparative absence of hyperthermia and constitutional disturbance, which is better marked though still slight in aphthous fever, and (e) by the absence of the intense and subtle infection of aphthous fever, which quickly attacks a whole herd and extends with equal rapidity over sheep, goats and pigs, attacking all cloven-footed animals virtually without exception. The cowpox patient, on the contrary, does not necessarily attack the cow in the next stall unless milked by the same hands, and spares heifers, bulls, steers, sheep, goats and pigs.

From the rinderpest cutaneous eruption it is easily distinguished by the presence of lymph in the lesion, that of rinderpest being a mere epidermic concretion; by the absence of the intense fever, anorexia and general constitutional disturbance, and of the early and high mortality which characterize that disease; by the absence of rapid and uniform infection of other cattle irrespective of a common milker; by the immunity of heifers, steers and bulls, which are speedily prostrated by rinderpest, and by the absence of the congestions and epithelial concretions of the mucosæ which characterize rinderpest.

From the leg irruption found in animals feeding on distiller’s swill and grains, or on the mast of beet sugar factories, by the history of the outbreak, of the dietary, of the seat and nature of the disease, and by the escape of animals living on a different aliment.

From the false cowpox (varicella) it is distinguished by the unilocular lesion of the latter, its absence of areola, and its rapid pustulation and drying, in five or six days into a thin papery crust instead of a thick, firm, umbilicated scab, as in cowpox. Varicella is further liable to appear in successive crops and thus last for several weeks.

The streptococcus eruption on teats and udder, is marked by the formation of abscesses of various sizes from a simple pustule upward, by the unilocular condition of the pus sac, by its tendency to invade the deeper tissues, and by its rupture and granulation without the formation of the thick umbilicated scab of cowpox.

The hard warty growths on the teats which last for weeks or months should never be mistaken for cowpox.

Cowpox usually lasts for some weeks in a herd, the duration depending on the number of susceptible animals and, whether these are habitually milked by the same person.

Course. Prognosis. It is a mild affection, which does not endanger life, yet it causes considerable loss through diminution of the milk secretion and, it may be, altered character of the milk, through the persistent sores and ulcers of the teats, through inflammation of the mammæ, and through an acquired habit of kicking.

Treatment is rarely needed. Any costiveness should be corrected by a cooling saline laxative (½ to 1 lb. Epsom salts) or by soft food, and milking should be done with great care to prevent rupture of the vesicles and the formation of sores. A teat tube may be used if necessary. Sores may be dressed with bland ointment. An ounce each of spermacetti and sweet almond oil with half a dram of gum myrrh. Or the vesicles or sores may be washed after each milking with a solution of 2 drams hyposulphite of soda in 1 quart water.

SHEEPPOX. VARIOLA OVINA.

Synonyms. Pocks; Peltrot; Clavelee, Picotte, (Fr.).

Definition. An acute febrile affection, eminently contagious, prevailing epizoötically in sheep and goats, characterized by early and marked hyperthermia, and general constitutional disorder, followed by the appearance on the bare or merely hairy portions of the skin, of diffuse redness becoming intensified in points, a rounded papular eruption, passing into vesicles, pustules and scabs, which latter dry up and drop off in 15 to 20 days.

Pathogenesis. Beside sheep and goats which contract the disease by exposure, the following genera have been successfully inoculated: ox, dog, pig, horse.

Forms. Two typical forms are recognized: (a) the discrete, regular or benign, in which the vesicles remain relatively few, and well isolated from each other, and (b) the confluent, irregular or malignant in which the vesicles are generally diffused over the body, even on the parts covered by wool, and set so close together that they merge into each other forming extensive continuous lesions. Other forms are the hæmorrhagic, purple or black sheeppox, the volante or intermittent kind, etc.

Geographical Distribution. Formerly common in Central and Western Europe, it still prevails continuously in the Balkans, the Danubian Principalities, Italy, Spain, the South of France and Algiers. Like other forms of variola, its permanent home is in Asia.

Causes. Long before the advent of modern bacteriology, sheeppox was held to be always and everywhere the result of contagion alone. Whenever it entered a new locality it was as the result of the importation of an affected sheep or one of its products; insular places like England maintained a permanent immunity, though the disease prevailed on the other side of the narrow straits or channel; yet when imported (1847 and 1862) it demonstrated a general susceptibility of the flocks on exposure or inoculation; more distant lands (America, Australia, Tasmania, South Africa, etc.) in the absence of imported infection remain clear to the present day.

The infection is more intense and diffusible than that of cowpox and horsepox following in this the smallpox of man. Absolute contact is not necessary, in either case the infection is carried in the air either on dust or otherwise, and above all in a confined building, a crowded sheep fold or a dusty highway.

In all forms of variola the virulence is concentrated in the lymph of the vesicle, and in horsepox and cowpox it is largely confined to this, whilst in sheeppox in severe cases it must also at times infect the blood, as lambs are occasionally born with sheeppox. On this basis the infection of the secretions generally has been advocated, but it is to be supposed that in moderate cases these are contaminated after secretion. Nocard and Roux produced immunity by the transfusion of blood from the sick to the healthy, but in no case a variolous eruption. Even the serosity from the swollen lymph glands failed to convey the disease.

In view of the diffusible nature of the germ, however, we must recognize that all secretions may be quickly contaminated as soon as they are exposed, and therefore no product of a sick or suspected sheep can be held to be safe, and all should be treated as presumably infected. The most dangerous products and those most liable to convey the disease are wool, hides, litter, buildings, yards, covers, parks, railway cars, boats, manure, urine and milk.