Part 52

Living creatures like men, dogs, cats, birds, vermin, flies and other predacious insects are occasional bearers of infection.

Receptivity must be considered in every case. In countries and districts habitually immune from sheeppox, all breeds appear to be equally susceptible, the only refractory specimens being sheep that have survived a first attack, and lambs born of ewes that had the disease (naturally or inoculated) during the later stages of gestation. New born lambs, on an exclusively milk diet, are alleged to be somewhat refractory. In a country where sheeppox has prevailed long and extensively, as in Algiers and Brittany, certain breeds of sheep seem to have attained to a large measure of immunity (Nocard). This is doubtless largely due to the survival of the more insusceptible strains of blood, as Algerian sheep carried into France lead to most virulent outbreaks among the native animals (Galtier).

This relative immunity is still more decided when we come to animals of other genera. Though the latest results of research seem to identify the sporidia found in the different forms of variola, yet the long habit of living in an environment found in the ovine race unfits the germ for pathogenic life in various other genera that have their own variolæ. Sacco and Villain reported inoculations from sheep to man, but as the first was experimenting with variola at the same time, and the second did not test his pustules by reinoculation the results are not convincing. Küchenmeister had a general eruption in sheep after intravenous injection of variola of man, but failed to test it by reinoculation. Voisin and Nocard on the other hand were uniformly unsuccessful in attempts to convey sheeppox to man, and the handling of variolous flocks from time immemorial must have led to many cases in man, had he been appreciably receptive. It is virtually the same with cowpox. Huzard vaccinated 2,000 sheep without producing immunity from sheeppox. Voisin had precisely similar results. He further inoculated infants with sheeppox, and later, successfully, with vaccine lymph.

It does not follow that these genera would be insusceptible under all conditions. Yet the failure to immunize against each other would argue a wider divergence of sheeppox and cowpox, than of smallpox and cowpox, or than of bovine and avian tuberculosis.

Galtier failed to inoculate sheeppox on rabbits or Guinea pigs, yet Jourdan, records a destructive outbreak in the Alps, in hares, kept in the same places with variolous sheep.

Accessory External Causes. All unwholesome conditions of life, and especially overcrowding, filth, starvation, and neglect contribute to the extension of the infection. Still more so, the importation of sheep, whether in the parks of armies, or in the channels of trade, by rail, or steamboat, through stockyards or markets.

The virus is possessed of unusual vitality, and in the dried condition, secluded from air and light will remain virulent for an indefinite period. Hence the danger of wool, and dried sheepskins. Even in the moisture of an ordinary shed it has retained its infectiveness for five or six months. The sheep that has recovered from the affection may transmit the disease to others for a period of six weeks. The virulence is rapidly destroyed by exposure to free air and sunshine, by a high temperature (140° F.), by dilute HCl (2:100), by carbolic acid (2:100), by zinc chloride (5:100), by potassæ permanganas (10:100), by lime chloride (4:100), or indeed by any of the strong antiseptics.

Incubation. This extends from four to seven days on an average, with a minimum of two and a maximum of twenty days. The conditions favoring an early eruption are youth, high condition, and a hot season, or close warm building, with overcrowding. Those favoring a tardy eruption are old age, debility, and above all a cold or wet season with exposure in the open air. Simonds, who inoculated in England in the cold months (October and November) never saw it exceed 13 days. In certain cases, however when the eruption had already commenced in mild weather, the sudden occurrence of a week of cold and wet, would stop it short to start anew on the return of warm weather a week later. In inoculated cases the incubation is shortened, while it is prolonged when the virus is introduced by the digestive or respiratory passages.

Symptoms. During the last two or three days of a prolonged incubation and especially in old sheep, there may be some impairment of appetite and rumination, dulness, a stiffness of movement of the hind limbs, and a disposition to lag behind the flock. The temperature may even have risen (104.5° F.), yet Simonds has never seen the febrile symptoms precede the eruption.

There follow, trembling, or rigors, accelerated pulse (80 to 90) and breathing, arched back, anorexia, suspension of rumination, costiveness, redness of the eyes, epiphora, a watery discharge from the nose, gradually becoming more viscid, and a marked hyperthermia (105°, 106° or 107° F.) If the skin is white, a blush, with some heat, is shown in the seat of the future eruption, usually on the parts uncovered by wool, the axillæ, sternum, abdomen, udder, inner sides of the thighs, lower surface of the tail, and the face—especially the eyelids, nostrils and lips.

In two days more, deep red points, like flea bites, appear more or less numerously, in the congested parts of the skin, and in twenty-four hours these have increased to firm rounded papules which are felt to extend into the true skin. These vary in size from 3 to 12 mm. or more. In two or three days the papule has become firmer and less tender, and shows in the centre a paler area where the exudation has resolved it into a vesicle. The characteristic sheeppox vesicle is rounded or flattened on its summit, being rarely pointed as in smallpox, or umbilicated as in cowpox. It is usually surrounded by a pink zone, which is at times infiltrated, firm and resistant. After about the sixth day, the vesicle becomes yellowish from the formation of pus. The pustules, with the surrounding tumefaction, encrease for about three days, when if they have not become confluent nor infected, they begin to dry up, acquiring a grayish crust on the surface which gradually encreases to a thick scab, which in five or six days more is detached leaving a pink, pitted spot covered by forming epidermis. Sometimes no distinct scab forms, but the crust dries, cracks up, and falls off in scales.

All the vesicles do not appear at once, but some earlier and some later, so that the successive stages of the eruption may be often seen together on the same subject, and the case is thereby materially prolonged.

As in other forms of variola the hyperthermia usually subsides with the appearance of the eruption, but as often reappears in some measure with pustulation (secondary fever of reaction), and becomes more severe in proportion to the extent and confluence of the eruption and the occurrence of complex infection.

The eruption may invade the conjunctiva, the cornea (inducing blindness), the nasal mucosa (causing difficult breathing), the mouth (salivation, difficult mastication), the pharynx (difficult deglutition), the stomach and intestines (diarrhœa), the bronchia (cough), or the vulva.

With the occurrence of desiccation, in discrete cases, the fever subsides, the swelling of the skin and head disappears, the discharges from the nose and eyes cease, and the animal is restored to health.

A secondary eruption will sometimes take place, but only papules form, which disappear without reaching maturity.

The duration of discrete sheep pox is usually about three weeks, but it may reach four in cool weather. It is more rapid and more prone to dangerous complications in hot weather. As the members of a flock are usually attacked in succession, it may take three months to pass through a flock.

In confluent or complicated cases the fever of invasion is very high, the sheep dull, prostrate, tender to touch along the back and loins particularly, with hurried, labored, panting, breathing, and mawkish, fevered breath, the weakness increases rapidly, standing even may become difficult, the wool is loosened and falls off in patches, the exposed skin is red, shading, it may be, into a violet hue. The head droops, the lips and nostrils swell, saliva drivels abundantly, anorexia is complete, though thirst may be ardent, a yellowish and even reddish, fœtid discharge may flow from the nose, respiration is difficult, the eyes are watery and deeply sunken, and the head, limbs, breast and abdomen are extensively infiltrated and œdematous.

Fever does not subside with the occurrence of eruption, which may appear thickly over the whole body, the woolly parts as well as the bare or hairy. The vesicles, which have often a dark, unhealthy look, tend to become confluent, and instead of proceeding regularly to maturity, they may remain hard or indolent papules or nodules or blacken and dry up. The secretion, when it takes place, is liable to be a thick, yellowish, fœtid pus. The eruption has much more tendency than with the discrete form to invade mucosæ, and not infrequently the serosæ are involved, especially those covering the lungs, liver and spleen. In the worst cases death may result from the fever before any eruption has taken place, in other cases the extent of the internal lesions tends to hasten a fatal result. With the amount of care that can be given to a flock, confluent cases are usually fatal.

In connection with the itching and scratching of the nose, abrasions and complex infections ensue, resulting in extensive ulceration and gangrene implicating the nasal cartilages and bones. The eruption around the pasterns may lead to shedding of the hoofs, and sloughing of the whole digital structures. Suppurating and gangrenous swellings form subcutaneously and in the lymph glands with fatal results. Blindness is especially liable to happen from the formation of the eruption on the conjunctiva and cornea. Ulcerations and sloughs are common on the internal mucosæ, and even on the serosæ. In implication of the abdominal organs, a fœtid diarrhœa is usually present, and in pregnant ewes abortion is the usual result.

Lesions. The cutaneous lesions are in their multilocular structure, the same as in cowpox, but differ materially in size and form. The typical vesicle is small (5 to 12 mm.), and neither broad and umbilicated like cowpox, nor conical and pointed as in smallpox, but round with a slight flattening on the summit. On the same animal may often be found all the successive stages at once, red points or hæmorrhagic spots, vesiculation, pustulation and even desiccation. The early changes are seen in the papillary layer and rete mucosum, in the form of swelling and congestion of the papillæ, exudation, active proliferation of the epidermic and tissue cells, and migration of leucocytes, (embryonic cells polynuclear) vacuolation of the papule, the spaces being filled with a straw colored exudate, and finally, the replacing of this by pus. If the local inflammation is very acute, the pustule may be resolved into a small abscess. On section of the skin the affected parts are found to be the seat of congestion and gelatinoid exudation, extending into the subcutaneous and intermuscular connective tissue, and even the muscles themselves are blackish and their capillaries engorged. The exudation is especially abundant in the dependent parts (head, neck, sternal and abdominal regions, legs). In proportion to the severity of the attack there are congestion, exudation, swelling, and blood extravasation in the lymph glands.

The nasal mucosa is congested, thickened or even ulcerated with abundant, tenacious, muco-purulent secretion and the nasal chambers narrowed or obstructed, and similar changes may be present in the larynx, trachea and bronchia. Spots of ecchymosis and even distinct variolous vesicles are to be expected. The pleuræ are often the seat of congestion, petechiæ, exudation, and discoloration (red or pale). The lung may show congestion and hepatisation in circumscribed areas, or there may be on the surface of such hepatised portions red or grayish foci, like a lentil, pea or bean, the seat of degeneration or forming minute abscesses. The pericardium and myocardium may be involved to a limited extent.

The buccal and pharyngeal mucosæ may be the seats of vesicles, or erosions or ulcers the result of their destruction, and the gastro-intestinal mucosa presents ecchymoses, vesicles, abrasions, and open sores in the midst of inflamed catarrhal patches. The mesenteric and other lymph glands are congested, swollen, softened and friable. Congestions and petechiæ are found on the peritoneum, liver, spleen and kidneys, with, at times, nodular foci. In certain cases congestions and effusions have been found on the pia mater and arachnoid, in the cerebral ventricles and the brain substance.

Prognosis. Mortality. Mortality varies much with the severity of the special outbreak and the conditions of life, favorable or otherwise, in which the flock is placed. In the milder forms the mortality may not exceed seven per cent, while in the more violent the whole flock almost may perish. A fatality of 20 to 30 per cent is the general average. Yet the inoculated form kills but 2 per cent.

If at the outset there is great weakness and prostration, complete anorexia and high fever, the prospect is discouraging. If the fever is moderate and strength and appetite retained, the case is very hopeful. On its first advent into a new country it causes a far greater mortality than after it has been long domiciled there, and frequent outbreaks have killed off the more susceptible strains of blood. Again very hot weather, or, still more, the prevalence of cold, drenching rains aggravates an outbreak and greatly encreases the fatality.

The loss is not to be measured by the deaths alone. The failure of the crop of lambs, through abortion, the shedding of wool, the loss of sight, hearing, hoofs, digits, flesh, stamina, etc, render recovery far from desirable, in the worst cases, as the animal fails to thrive or pay for its keep. On the contrary it is immune from any future attack, and if left in a thrifty condition it becomes especially valuable in a district where sheeppox prevails.

Treatment. Once established in the system the disease will follow its regular course, through all its stages. Yet we can, by dieting, pure air, cleanliness, shelter and even by medicinal measures, do much to render that course a safe one. Cool sheds, pure air, clean floor, dry clean litter and shelter from rain are above all important. The sheep may be separated in different enclosures in small lots of 5 or 6 to prevent crowding, heating, and excitement, and in any case the infected should be removed from the noninfected, and even from each other to avoid infection and reinfection. This is especially requisite in hot weather.

For the strong and vigorous, a diet of sliced roots and meal (oat, bran, linseed, barley, wheat middlings) is good, while for the weak, gruels of oat meal, barley meal, linseed meal, or the same agents dry, may be given. Powdered saltpeter may be given in this (1 oz. to 8 or 10 sheep) and common salt allowed to be licked at will. Drinking water may be given pure, or slightly acidulated with sulphuric or hydrochloric acid, or hyposulphite or bisulphite of soda may be used as a substitute for the latter. The bowels are usually costive, and may be relieved at first by 3 ozs. of sodic sulphate, and later, if need be, by soapy injections. Often during the course of the disease a sudden access of fever may be cut short by a mild laxative, if that is not contra-indicated by existing diarrhœa.