Chapter 64

Variola in the horse, while it is identical in principle, general course, complications, and lesions with variola in other animals, is a disease of the horse itself, and is not transmissible in the form of variola to any other animal; nor is the variola of any other animal transmissible to the horse. Cattle and men, if inoculated from a case of horsepox, develop vaccinia, but vaccinia from the latter animals is not so readily reinoculated into the horse with success. If it does develop, it produces the original disease.

_Causes._--The direct cause of horsepox is infection. A large number of predisposing causes favor the development of the disease, as in the case of strangles, and this trouble, like almost all contagious diseases, renders the animal which has had one attack immune. The chief predisposing cause is youthfulness. Old horses which have not been affected are less liable to become infected when exposed than younger ones. The exposure incident to shipment, through public stables, cars, etc., acts as a predisposing cause, as in the other infectious diseases. The period of final dentition is a time which renders it peculiarly susceptible.

Dupaul states that the infection is transmissible through the atmosphere for several hundred yards. The more common means of contagion is by direct contact or by means of fomites. Feed boxes and bridles previously used by horses affected with variola are probably the most frequent carriers of the virus, and we find the lesions in the majority of cases developed in the neighborhood of the lips and nostrils. Coition is a frequent cause. A stallion suffering from this disease may be the cause of a considerable epizootic, as he transmits it to a number of brood mares and they in turn return to the farms where they are surrounded by young animals to which they convey the contagion. The saddle and croup straps are frequent agents of infection. The presence of a wound greatly favors the inoculation of the disease, which is also sometimes carried by surgical instruments or sponges. Trasbot recites a case in which a set of hobbles, which had been used on an animal suffering from variola, were used on a horse for a quittor operation and transmitted the disease, which developed on the edges of the wound.

_Symptoms._--There is a period of incubation, after an animal has been exposed, of from five to eight days, during which there is no appreciable alteration in the health. This period is shorter in summer than in winter. At the end of this time small nodes develop at the point of inoculation and the animal becomes feverish. The horse is dull and dejected, loses its appetite, and has a rough, dry coat with the hairs on end. There is moderate thirst. The respirations are somewhat quickened and the pulse becomes rapid and full. The body temperature is elevated, frequently reaching 104° or 105° F. within 36 or 48 hours from the appearance of the first symptoms.

The visible mucous membranes, especially the conjunctivæ, are of a bright rosy red. In the lymphatic, cold-blooded, and more common horses these symptoms of fever are less marked; even with a comparatively high temperature the animal may retain its appetite and work comparatively well, but these cases, if worked and overheated, are liable to develop serious complications.

At the end of from three and a half to four days the eruption breaks out, the fever abates, and the general symptoms improve. The eruption in severe cases may be generalized; it may be confined to the softer skin of the nose and lips, the genital organs, and the inside of the thighs, or it may be localized in the neighborhood of a wound or in the irritated skin of a pair of greasy heels. It consists of a varying number of little nodes which, on a mucous membrane, as in the nostrils or vagina, or on soft, unpigmented skin, appear red and feel at first like shot under the epidermis. These nodes soften and show a yellowish spot in the center when they become pustules. The epidermis is dissolved and the matter escapes as a viscid fluid at first citrine and later cloudy and purulent, which dries rapidly, forming scabs; if these fall off or are removed they leave a little shallow, concave ulcer which heals in the course of five or six days. In the softer skin if pigmented the cicatrices are white and frequently remain so for about a year, when the pigment returns. The lips or genital organs of a colored horse, if covered with a number of small white spots about the size of a pea, will usually indicate that the animal has been affected with the horsepox.

At times the pustules may become confluent and produce large, superficial, serpentine ulcers on the membrane of the nostrils, around the lips or eyelids, or on the borders of wounds and in greasy heels; in this case the part becomes swollen, hot, painful, and is covered with a profuse discharge of matter. In this form there is frequently a secondary fever lasting for a day or two.

In severe cases there may be a suppurative adenitis, or inflammation of the lymphatic glands which are fed from the affected part. If the eruption is around the nostrils and lips, the glands between the jaws (submaxillary) form abscesses as in a case of strangles; if the eruption is in a pair of greasy heels abscesses may form in the fold of the groin (inguinal). There may be so much tumefaction of the nostrils as to produce difficulty in breathing.

_Complications._--A case of horsepox may be attended with various complications of varying degrees of importance. Adenitis, or suppuration of the glands, has just been mentioned. Confluent eruptions irritate the part and induce the animal to rub the inflamed part against the manger or scratch it in other ways and thus produce troublesome ulcers, which may leave ugly scars. Irritation of the mucous membrane of the nose causes severe coryza with purulent discharge.

The eruption may occur in the throat or in the air tubes to the lungs, developing an acute laryngitis or bronchitis. If the animal is exposed to cold, or worked so as to engorge the lungs with blood at the termination of the specific fever, just when the eruption is about to localize, it may be determined to the lungs. In this case we have a short, dry cough, labored breathing, the development of a secondary fever of some gravity, and all the external symptoms of a pneumonia. This pneumonia differs, however, from an ordinary pneumonia in the symptoms furnished by the examination of the lungs themselves. In place of a large mass of the lung tissue being affected the inflammation is disseminated in smaller spots over the entire lung.

_Diagnosis._--The diagnosis of horsepox is to be based on the presence of a continuous fever, with rosy mucous membranes, for several days and the appearance of the characteristic eruption. If the eruption is in the nasal cavities, marked by a considerable discharge and attended with submaxillary abscesses, it may be confounded with strangles. If the throat is affected, it may be confounded with an angina (laryngitis or pharyngitis), but in the latter the local trouble precedes or is concomitant with the fever, while in the former the fever precedes the local trouble by several days. Variola may be confounded with bronchitis or pneumonia if complicated with these troubles and the eruption is absent from the exterior, but it is of little moment, as the treatment for both is much the same. When the eruption is in the neighborhood of the genital organs the disease has been mistaken for dourine. In variola the eruption is a temporary one; the nodes and pustules are followed by shallow ulcers and rapid cicatrization unless continued in the vagina or on the penis by the rubbing of the walls and filth which accumulates; there are apt to be pustules at other parts of the body. In the venereal disease the local trouble commences as a papule and breaks into an ulcer without having formed a pustule. The ulcer has not the convex rosy appearance of that of the less serious discharge; the symptoms last for a longer period, by which time others aid in differentiating the two. In glanders the tubercle is hard and, after breaking into an ulcer, the indurated bottom remains, grayish or dirty white in color, ragged, and exuding a viscous, oily discharge. There is no disposition to suppuration of the neighboring glands. In variola the rosy shallow ulcer and healthy pus, with the acutely tumefied glands, should not be mistaken, at least after a day. I have seen in mules acute glanders which required a day's delay to differentiate from strangles; at that time the farcy buds appeared.

_Prognosis._--The average case of horsepox runs a course of dejection, loss of appetite, and more or less fever for about four days, followed by a rapid convalescence, and leaves the animal as well and as sound as before. If the eruption has been excessive or confluent, the ulcerations may act as irritants and render the animal unfit for use for several weeks. Laryngitis, pharyngitis, bronchitis, and pneumonia in this disease are not of greater gravity than they are when occurring from other causes. The spots denuded of pigment left by the pustules on the lips and genitals may temporarily depreciate the value of the animal to a slight degree.

_Treatment._--As this is a disease unattended by alterations of the blood itself, although a specific fever, and is of a sthenic type, active remedies are admissible and indicated. The horse should be placed on a low diet (little or no oats)--bran mashes, a moderate quantity of good, sound hay, a few carrots or apples, which will act as laxatives; also slop feed. Barley flour is more cooling for mashes than bran or oatmeal. Water may be given as the animal desires it, but it should not be cold; if a half bucketful of water is kept in the manger, the horse will take but a few swallows at a time. One-dram doses of nitrate of potash or 1-ounce doses of sweet spirits of niter are useful in the drinking water. If the fever is high, the antipyretics are indicated: Sulphate of quinin in 1-dram doses; iodid of potash in 1-dram doses; infusion of pine tops, of juniper leaves, of the aromatic herbs, or of English breakfast tea are useful in the later stages. If complications of the air passages or lungs are threatened, a large mustard poultice should be applied to the belly and sides of the chest. Oxid of zinc ointment should be used on confluent eruptions, and if the ulceration is excessive it may have to be touched with caustic.

Great care must be taken to keep the animal protected from cold drafts of air or other exposure. Blankets or sheets should be used on the body and bandages on the legs. After convalescence is established, nutritious feed of easy digestion and walking exercise are all that is needed, except perhaps a little Glauber's salt to prevent constipation.

_Prophylactic treatment._--When horsepox breaks out among a large number of horses, especially on a farm where there are a number of colts, it may be assumed that the greater majority will contract the disease, and it is more economical that they should have it and be through with it at once. If the weather is moderate, all the animals which have not been affected can be inoculated, which will produce the disease in a mild form, with the eruption at a point of election, and render the danger of complication a minimum one. For inoculation the discharge from the pustules of a mild case should be selected and inoculated by scarification on the belly or the under surface of the neck.

ANTHRAX.

_Synonyms:_ Carbuncle, splenic fever, splenic apoplexy, etc.; charbon, sang de rate (French); Miltzbrand (German).

_Definition._--Anthrax is a severe and usually fatal contagious disease, characterized by chills, great depression and stupor of the animal, and a profound alteration of the blood. It is caused by the entrance into the animal's body of a bacterium, known as the _Bacillus anthracis_, or its spores.

Practically all animals are susceptible to anthrax. The herbivora are especially susceptible, in the following order: The sheep, the ox, and the horse. The guinea pig, the hog, the rabbit, mice, and other animals die quickly from its effects. Man, the dog, and other omnivora and carnivora may be attacked by it in a constitutional form as fatal as in the herbivora, but fortunately in many cases develop from it only local trouble, followed by recovery.

Anthrax has been a scourge of the animals of the civilized world since the first written history we have of any of their diseases. In 1709-1712 extensive outbreaks of anthrax occurred in Germany, Hungary, and Poland. In the first half of the nineteenth century it had become an extensively spread disease in Russia, Holland, and England, and for the last century has been gradually spreading in the Americas, more so in South America than here. In 1864, in the five governments of Petersburg, Novgorod, Olonetz, Twer, and Jaroslaw, in Russia, more than 10,000 horses and nearly 1,000 persons perished from the disease.

_Causes._--The causes of anthrax were for a long time attributed entirely to climatic influence, soil, and atmospheric temperature, and they are still recognized as predisposing factors in the development of the disease, for it is usually found, especially when outbreaks in a great number of animals occur, in low, damp, marshy countries during the warm seasons. It is more frequent in districts where marshy lands dry out during the heat of summer and are then covered with light rains. Decaying vegetable matter seems most favorable for nourishing and preserving the virus.

The direct cause of anthrax is always infection of a previously sound animal, either directly from a diseased animal or through various media which contain excretions or the débris from the body of one previously infected.

The specific virus of anthrax was first discovered by Davaine in 1851. He recognized microscopic bodies in the form of little rods in the blood of animals suffering from anthrax. It was not, however, till a quarter of a century later that Pasteur defined the exact nature of the bacillus, the mode of its propagation, and its exact relationship to anthrax as the sole cause of the disease. In the animal body the bacilli have a tendency to accumulate in the spleen, liver, and elsewhere, so that these organs are much more virulent than the muscles or less vascular tissues. When eliminated from the animal in the excretions, or when exposed to outside influences by the death of the animal and the disintegration of the tissues, the body of the rod is destroyed and the spores only remain. These spores, which may be called the seeds of the bacilli, retain their vitality for a long period; they resist ordinary putrefaction; they are unchanged by moisture; and they are not affected by moderate heat. If scattered with the débris of a dead animal on the surface of the ground, they may remain around the roots of the grass in a pasture or may be washed to the nearest low-lying ground or marsh. If buried in the body of an animal dead from anthrax, they may be washed deep into the ground, and in later years (in one proved case 17 years) be brought to the surface and infect other animals. They are frequently brought to the surface of the earth, having been swallowed by earthworms, in the bodies of which they have been found.

This accounts for the outbreaks at the time of the first rains after a dry season. During the latter the earthworm goes deep in the ground in search of moisture; it finds the spore which has been washed there in past years, swallows it, and afterwards brings it to the surface. The virus is carried with the wool from infected sheep and remains in it through the process of manufacture into cloth. The spores remain in the hides of animals which have died of anthrax and retain their vitality throughout months of soaking in the tanners' pits, the working of the harness maker or the cobbler, and after the oiling of the completed leather. The dried spores in the dust from any of these products may be carried by the atmosphere.

Infection of an animal takes place through inoculation or contact of the bacillus or its spores with an abraded surface or mucous membrane, on a sound animal. In an infected district horses may eat with impunity the rich pasturage of spring and early summer, but when grass gets low they crop it close to the ground, pull up the roots around which the virus may be lodged, and under these conditions the animals are more apt to have abrasions of the lips or tongue by contact with dried stubble and the dirt on the roots; this favors the introduction of the germs into the system. The virus may be introduced with feed and enter the blood-vessel system from the stomach and intestines. If in the dust, dried hay, or on the parched pasture of late summer, the virus may be inhaled and be absorbed from the lining of the lungs. If in harness leather, it needs but an abrasion of the skin, as the harness rubs it, to transfer the spore from the leather to the circulation of the animal.

The writer saw a case of anthrax occur in a groom from the use of a new horse brush. The strap which passes over the back of the hand inoculated an abrasion on the knuckle of the first finger, and in 12 hours a "pustule" had formed and the arm had become infected.

_Symptoms._--The symptoms of anthrax usually develop with extreme rapidity. The horse is dejected and falls into a state of profound stupor, attended with great muscular weakness. The feeble, indolent animal, if forced to move, drags its legs. There are severe chills, agitation of the muscles, symptoms of vertigo, and at times colicky pains. The mucous membranes turn a deep ocher or bluish-red color. The body temperature is rapidly elevated to 104° or 105° F. The breathing is increased to 30 or 40 respirations in the minute and the pulse is greatly accelerated, but while the arteries are soft and almost imperceptible, the heart beats can be felt and heard, violent and tumultuous. In some cases, when inoculation is through the skin, large subcutaneous swellings appear; these may involve a leg, a shoulder, one side of the body, or the neck or head. The swelling is at first hot and painful, but afterwards it becomes necrotic and sensation is lost. The symptoms last but two, three, or four days at most, when the case usually terminates fatally. An examination of the blood shows a dark fluid which will not clot, and which remains black after exposure to the air. After death the bodies putrefy rapidly and bloat up; the tissues are filled with gases, and a bloody foam exudes from the mouth, nostrils, and anus, and frequently the mucous membranes of the rectum protrude from the latter. The hairs detach from the skin. Congestion of all the organs and tissues is found, with interstitial hemorrhages. The muscles are friable and are covered with ecchymotic spots. This is especially marked in the heart.

The black, uncoagulated, and incoagulable blood shows an iridescent scum on its surface, which is due to the fat of the animal dissolved by the ammonia produced by the decomposed tissues. The serum oozes out of every tissue and contains broken-down blood, which, when examined microscopically, is found to have the red globules crenated and the leucocytes granular. A high power of the microscope also reveals the bacteria in the shape of little rodlike bodies of homogeneous texture with their brilliant spores.

The lymphatic ganglia are increased four, five, six, or ten times their natural size, enlarged by the engorgement of blood. The spleen shows nodulated black spots containing a muddy blood, which is found teeming with the virus. This organ is much enlarged and is quite friable. The mucous membranes of the intestines are congested and reddish brown; the surface of the intestines is in many places denuded of its lining membrane, showing fissures and hemorrhagic spots. The liver has a cooked appearance; the kidneys are congested and friable; the urine is red; the pleura, lungs, and the meninges are congested, and the bronchi of the lungs contain a bloody foam.

_Treatment._--Treatment of anthrax in animals by medicinal means has not proved satisfactory. In cases of local anthrax an incision of the swelling followed by the application of disinfectants sometimes causes good results. In such cases, however, the danger of disseminating the infection from the wounds tends to make this procedure inadvisable unless great care is taken.

Good results are obtained from the use of serum in the treatment of the disease. For this purpose 30 to 100 cubic centimeters should be administered subcutaneously or intravenously. If no improvement is noticed within 24 hours the injection should be repeated. In a number of instances afforded to test the curative value of the serum in cases of anthrax in man and animals splendid results were obtained.

The prophylactic treatment formerly consisted in the avoidance of certain fields and marshes which were recognized as contaminated during the months of August and September and had been occupied the years in which the outbreaks usually occurred. It underwent, however, a revolution after the discovery by Pasteur of the possibility of a prophylactic inoculation or vaccination which granted immunity from future attacks of the disease similar to that granted by the recovery of an animal from an ordinary attack of the disease.

This treatment consists in the use of a vaccine which is made by the artificial cultivation of the virus of anthrax in broth and in the treatment of it by means of continued exposure to a high temperature for a certain time, which weakens the virus to such extent that it is capable of producing only a very mild and not dangerous attack of anthrax in the animal in which it is inoculated, and thus protects it from inoculation of a stronger virus. The production of this virus, which is carried on in some countries at the expense of the governments and is furnished at a small cost to the farmers in regions where the disease prevails, in this country is made in private laboratories only.

At the present time very good results are being obtained with vaccination consisting of an injection of highly potent anthrax serum on one side of the animal and a vaccine on the other side. This method of treatment requires only a single handling of the animals and further possesses advantages over the Pasteur treatment in that it immediately makes animals immune. In the numerous applications of this form of treatment very good results have been obtained and the immunity produced thereby visually lasts at least one year. The vaccinated animals should be kept for a period of ten days to two weeks from exposure, since during that period they are at times even more susceptible to the disease, and therefore care should be taken not to reduce their vitality.