SPECIAL REPORT ON DISEASES OF CATTLE TEXT

scientists in recent times have definitely proved the entire dissimilarity of the two affections, both from a clinical and a causal standpoint. The disease is produced by a specific bacillus, readily distinguishable from that causing anthrax. (Pl. XXVIII, fig. 4.) Cattle between 6 months and 2 years of age are the most susceptible. Sucking calves under 6 months are rarely attacked, nor are they so susceptible to inoculation as older animals. Cattle more than 2 years of age may become affected, but such cases are infrequent. Sheep and goats may also contract the disease, but man, horses, hogs, dogs, cats, and fowls appear to be immune. Like anthrax, blackleg is more or less restricted to definite localities. There are certain pastures upon which the disease regularly appears in the summer and fall of the year. As to any peculiarities of the soil nothing is definitely known. Some authors are inclined to regard moist, undrained, and swampy pastures favorable to this disease, but these theories will hardly hold, as it is found in all kinds of soil, in all altitudes, at all seasons of the year, and under various climatic conditions. It occurs in this country from the Atlantic to the Pacific and from Mexico to Canada, but it is more prevalent in the Western and Southwestern States. In Europe it exists in France, various parts of Germany, in Belgium, Norway, Denmark, Italy, and in the Alps of Switzerland. In Africa it occurs in Algeria and to some extent in Natal and bordering countries. In South America it prevails quite extensively throughout Argentina. Cattle in Cuba and Australia also suffer. _Cause._--The cause of the disease is a bacillus resembling in some minor respects the anthrax bacillus and differing but little from it in size. It also possesses the power of forming within itself a spore. In Plate XXVIII, figure 4, this is represented as an uncolored spot located in one end of the rod, which is enlarged so that the rod itself appears more or less club-shaped. What has already been stated concerning the significance of the spore of the anthrax bacillus applies equally well to these bodies. They resist destructive agents for a considerable time, and may still produce disease when inoculated after several years of drying. This fact may account for the occasional appearance of blackleg in stables. In order to meet the requirements for the development of the spores, which takes place only in the absence of the atmosphere, it is necessary that the wound be very small and deep enough to penetrate the subcutaneous tissue. Several observers have found this organism in the mud of swamps. By placing a little of the mud under the skin, the disease has been produced. Since the disease may be produced by placing under the skin material containing the specific bacilli and spores, it has been assumed that cattle contract the disease through wounds, principally of the skin, or very rarely of the mouth, tongue, and throat. Slight wounds into which the virus may find access may be caused by barbed wire, stubbles, thorns, briers, grass burs, and sharp or pointed parts of feed. Infection by way of digestive tract is also probable. _Symptoms and lesions._--The symptoms of blackleg may be either of a general or of a local nature, though more frequently of the latter. The general symptoms are very much like those belonging to other acute infectious or bacterial diseases. They begin, from one to three days after the infection has taken place, with loss of appetite and of rumination, with dullness and debility, and a high fever. The temperature may rise to 107∞ F. To these may be added lameness or stiffness of one or more limbs, due to the tumor or swelling quite invariably accompanying the disease. After a period of disease lasting from one to three days the affected animal almost always succumbs. Death is preceded by increasing weakness, difficult breathing, and occasional attacks of violent convulsions. The most important characteristic of this disease is the appearance of a tumor or swelling under the skin a few hours after the setting in of the constitutional symptoms described above. In some cases it may appear first. This tumor may be on the thighs (hence "blackleg," "black quarter"), the neck, the shoulder, the breast, the flanks, or the rump; never below the carpal (or knee) and the hock joint. It more rarely appears in the throat and at the base of the tongue. The tumor, at first small and painful, spreads very rapidly both in depth and extent. When it is stroked or handled a peculiar crackling sound is heard under the skin; this is due to a collection of gas formed by the bacilli as they multiply. At this stage the skin becomes dry, parchment-like, and cool to the touch in the center of the tumor. If the swelling is cut into, a frothy, dark-red, rather disagreeable-smelling fluid is discharged. The animal manifests little or no pain during the operation. As it is frequently desirable to know whether the disease is anthrax or blackleg, a few of the most obvious post-mortem changes may here be cited. The characteristic tumor with its crackling sound when stroked has already been described. If after the death of the animal it is more thoroughly examined, it will be noted that the tissues under the skin are infiltrated with blood and yellowish, jellylike material and gas bubbles. The muscular tissue beneath the swelling may be brownish or black, shading into dark red. (Pl. XLII.) It is soft, easily torn and broken up. The muscle tissue is distended with numerous smaller or larger gas-filled cavities, often to such extent as to produce a resemblance to lung tissue. Upon incision it does not collapse perceptibly, as the gas cavities are not connected with one another. In the abdomen and the thorax bloodstained fluid is not infrequently found, together with bloodstaining of the lining membrane of these cavities. Blood spots (or ecchymoses) are also found on the heart and lungs. The liver is congested, but the spleen is always normal in appearance. _Differential diagnosis._--Among the features of this disease which distinguish it from anthrax may be mentioned the unchanged spleen and the ready clotting of the blood. It will be remembered that in anthrax the spleen (milt) is very much enlarged, the blood tarry, coagulating feebly. The anthrax carbuncles and swellings differ from the blackleg swellings in not containing gas, in being hard and solid, and in causing death less rapidly. It is difficult to distinguish between the swellings of blackleg and malignant edema, as they resemble each other very closely and both are distended with gas. Malignant edema, however, generally starts from a wound of considerable size; it usually follows surgical operations, and seldom results from the small abrasions and pricks to which animals are subjected in pastures. Inoculation experiments on guinea pigs, rabbits, and chickens will generally disclose the differences between the three diseases above, as all these species are killed by the germ of malignant edema, only the first two species by the anthrax bacillus, while the guinea pigs alone will succumb to the blackleg infection. Hemorrhagic septicemia may be differentiated from blackleg by its affecting cattle of all ages, by the location of the swelling usually about the region of the throat, neck, and dewlap, by the soft, doughy character of the swellings without the presence of gas bubbles, and finally by the characteristic hemorrhages widely distributed throughout the body. Other means of diagnosis, which have reference to the specific bacilli, to the inoculable character of the virus upon small animals, and which are of decisive and final importance, can be utilized only by the trained bacteriologist and veterinarian. _Treatment._--In this disease remedies have thus far proved unavailing. Some writers recommend the use of certain drugs, which seem to have been beneficial in a few cases, but a thorough trial has shown them to be valueless. Others advise that the swelling be opened by deep and long incisions and a strong disinfectant, such as a 5 per cent solution of carbolic acid, applied to the exposed parts; but this procedure can not be too strongly condemned. As nearly all those attacked die, in spite of every kind of treatment, and in view of the fact that when these tumors are opened the germs of the disease are scattered over the stables or pastures, thus becoming a source of danger to other cattle, it is obvious that such measures do more harm than good and should be put aside as dangerous. Bleeding, nerving, roweling, or setoning have likewise some adherents, but the evidence indicates that they have neither curative nor preventive value and therefore should be discarded for the method of vaccination which has been thoroughly tried and proved to be efficacious. _Prevention._--The various means suggested under "Anthrax" to prevent the spread or recurrence of this disease are equally applicable to blackleg, and hence do not need to be repeated here in full. They consist in the removal of well animals from the infected pasture to a noninfected field, the draining of the swampy ground, the burial or burning of the carcasses to prevent the dissemination of the germs over vast areas through the agency of dogs, wolves, buzzards, or crows, the disinfection of the stables and the ground where the animals lay at the time of death, and, if possible, the destruction of the germs on the infected pastures. One of the most effective methods for freeing an infected pasture from blackleg is to allow the grass to grow high, and when sufficiently dry to burn it off. One burning off is not sufficient to redeem an infected pasture, but the process should be repeated several years in succession. This method, however, is in many instances impracticable, as few cattle owners can afford to do it, and the only means left for the protection of the animals is vaccination. _Immunization by vaccination._--Three French veterinarians, Arloing, Cornevin, and Thomas, were the first to discover that cattle may be protected against blackleg by inoculation with virulent material obtained from animals which have died of this disease. Later they devised a method of inoculation with the attenuated or weakened blackleg spores which produced immunity from natural or artificial inoculation of virulent blackleg germs. Their method has undergone various modifications both in regard to the manufacture of the vaccine and in the mode of its application. Kitt, a German scientist, modified the method so that but one inoculation of the vaccine was required instead of two, as was the case with that made by the French investigators. The vaccine formerly prepared and distributed by the Bureau of Animal Industry combined the principle of Arloing, Cornevin, and Thomas, and the modification of Kitt. By vaccination we understand the injection of a minute amount of attenuated--that is, artificially weakened--blackleg virus into the system. This virus is obtained from animals which have died from blackleg, by securing the affected muscles, cutting them into strips, and drying them in the air. When they are perfectly dry they are pulverized and mixed with water to form a paste, smeared in a thin layer on flat dishes, placed in an oven, and heated for six hours at a temperature close to that of boiling water. The paste is then transformed into a hard crust, which is pulverized and sifted and distributed in packages containing either 10 or 25 doses. This constitutes the vaccine, the strength of which is thoroughly tested on experiment animals before it is distributed among the cattle owners. This vaccine, which is in the form of a brownish, dry powder, is mixed with definite quantities of sterile water, filtered, and by means of a hypodermic syringe the filtrate injected under the skin in front of the shoulder of the animal. The inoculation is usually followed by insignificant symptoms. In a few cases there is a slight rise of temperature, and by close observation a minute swelling may be noted at the point of inoculation. The immunity conferred in this way may last for 18 months, but animals vaccinated before they are 6 months old and those in badly infected districts should be revaccinated before the following blackleg season. The effect of the vaccine prepared by this bureau in preventing outbreaks of the disease and in immediately abating outbreaks already in progress was highly satisfactory, and it is not to be doubted that thousands of young cattle were saved to the stock owners during the 25 years in which the vaccine was distributed.[6] More than 47,000,000 doses were sent out during this period, and from reports received it is safe to conclude that more than 40,000,000 were actually injected, whereby the percentage of loss from blackleg has been reduced from 10 per cent, which annually occurred before using, to less than one-half of 1 per cent per annum. With these figures before us it is plain that the general introduction of preventive vaccination must be of material benefit to the cattle raisers in the infected districts. Moreover, there is every reason to believe that with the continued use of blackleg vaccine in all districts where the disease is known to occur, and an earnest effort on the part of the stock owners to prevent the reinfection of their pastures by following the directions given, blackleg may be kept in check and gradually eradicated. Immunization against blackleg is now frequently accomplished by the use of the so-called blackleg aggressin and blackleg filtrates. NECROTIC STOMATITIS (CALF DIPHTHERIA). [Pl. XLIII.] Necrotic stomatitis is an acute, specific, highly contagious inflammation of the mouth occurring in young cattle, and characterized locally by the formation of ulcers and caseo-necrotic patches and by constitutional symptoms, chiefly toxic. This disease has also been termed calf diphtheria, gangrenous stomatitis, ulcerative stomatitis, malignant stomatitis, tubercular stomatitis, and diphtheritic patches of the oral mucous membrane. _History._--During the last few years farmers and cattlemen in this country, especially in Colorado, Texas, and South Dakota, have increasingly noted the occurrence of enzootics of "sore mouth" among the young animals of their herds. Instead of healing, like the usual forms, of themselves, these cases, if untreated, die. Careful study of some of them has resulted in their identification with cases reported in 1877 by Dammann, from the shore of the Baltic; in 1878 by Blazekowic, in Slavonia; in 1879 by Vollers, in Holstein; in 1880 by Lenglen, in France; in 1881 by Macgillivray, in England; and in 1884 by Lˆffler, who isolated and described the microorganism which produces the disease. Bang obtained this organism from the diphtheritic lesions of calves in 1890, and Kitt likewise recovered the bacillus from similar lesions of the larynx and pharynx of calves and pigs in 1893. [Illustration: PLATE XLII. SECTION OF MUSCLE FROM A BLACKLEG SWELLING. a. GAS BUBBLES. b. CAVITIES DUE TO GAS FORMATION.] [Illustration: PLATE XLIII. NECROTIC STOMATITIS (CALF DIPTHERIA).] _Etiology._--The cause of necrotic stomatitis, as demonstrated by Lˆffler and since confirmed by other investigators, is _Bacillus necrophorus_, often spoken of as the bacillus of necrosis. This organism varies in form from a coccoid rod to long, wavy filaments, which may reach a length of 100µ; the width varies from 0.75µ to 1µ. Hence it is described as polymorphic. It does not stain by Gram, but takes the ordinary anilin dyes, often presenting, especially the longer forms, a beaded appearance. A characteristic of the organism, of great moment when we come to treatment, is that it grows only in the absence of oxygen, from which fact it is described as an obligate anÊrobe. Very few organisms exhibit a wider range of pathogenesis. According to clinical observation to the present time, _Bacillus necrophorus_ is pathogenic for cattle, horses, hogs, sheep, reindeer, kangaroos, antelope, and rabbits. Experimentally it has been proved pathogenic for rabbits and white mice. The dog, cat, guinea pig, pigeon, and chicken appear to be absolutely immune. It is not pathogenic for man. The importance of this bacillus is far beyond even its relation to necrotic stomatitis. Besides this disease it has been demonstrated as the causative factor in foot rot, multiple liver abscesses, disseminated liver necrosis, embolic necrosis of the lungs, necrosis of the heart, in cattle; gangrenous pox of the teats, diphtheria of the uterus and vagina, in cows; diphtheritic inflammation of the small intestine of calves. Among horses it is the agent in the production of necrotic malanders, quittor, and diphtheritic inflammation of the large intestine. In hogs it has caused necrotic or diphtheritic processes in the mucous membrane of the mouth, necrosis of the anterior wall of the nasal septum, and pulmonary and intestinal necrosis, accompanying hog cholera. Abscesses of the liver, gangrenous processes of the lips and nose, and gangrenous affections of the hoof have all been caused in sheep by this organism. _Pathology._--The principal lesions in necrotic stomatitis occur in the mucous membrane of the mouth and pharynx. The alterations may extend to the nasal cavities, the larynx, the trachea, the lung, the esophagus, the intestines, and to the hoof. The oral surfaces affected are, in the order of frequency, tongue, cheeks, hard palate, gums, lips, and pharynx. In the majority of cases the primary infection seems to occur in the tongue. (Pl. XLIII.) Infection takes place by inoculation. Some abrasion or break in the continuity of the mucous membrane of the mouth occurs. Very likely the origin may be connected with the eruption of the first teeth after birth, or, in animals somewhat older, the entrance of a sharp-pointed particle of feed. Gaining an entrance at this point, the bacilli begin to multiply. During their development they elaborate a toxin, or poisonous substance, which causes the death, or necrosis, of the epithelial, or superficial, layer of the mucous membrane and also of the white blood cells which have sallied forth through the vessel walls to the defense of the tissues against the bacillary attack. This destruction of the surface epithelium seems to be the essential factor in the production of the caseous patch, often called the false membrane. From the connective-tissue framework below is poured forth an inflammatory exudate highly albuminous or rich in fibrin-forming elements. When this exudate and the necrosed cellular elements come in contact, the latter furnish a fibrin ferment which transforms the exduate into a fibrinous mass. This process is known as coagulation necrosis, and the resulting fibroid mass, containing in its meshes the necrosed and degenerated epithelium and leucocytes, constitutes the diphtheritic or false membrane. Did the process cease at this point it would be properly called a diphtheritic inflammation, but it does not. A caseating ferment is supplied by the bacilli, and this, acting upon the fibroid patch, transforms it into a dry, finely granular, yellowish mass of tissue detritus resembling cheese. Frequently this caseous inflammation results in the formation of one or more ulcers with thickened, slightly reddened borders, surmounted by several layers of this necrosed tissue. The floor of the ulcer is formed by a grayish-yellow, corroded surface, under which the tissue is transformed into a dry, friable, or firm cheesy mass. In the tongue this may progress to two fingers' thickness into the muscular portion; in the cheek it may form an external opening, permitting fluids to escape from the mouth; upon the palate it frequently reaches and includes the bone in its destructive course; upon the gums it has produced necrosis of the tooth sockets,