Bacteriology. In a disease with such destructive changes in blood and tissues, bacteria are found, almost of necessity, in the seats of the lesions and even in the blood. No constant microörganism has, however, been isolated, cultivated in artificial cultures, and successfully inoculated on other and susceptible animals. Saweljeff isolated sporulating motile bacilli which break up into micrococci and streptococci, with the cultures of these on agar he produced what he believed to be cattle plague. Metchnikoff found a short bacillus with rounded ends, forming cocci and leptothrix-like threads, non-liquefying, and producing cattle plague in calves. Sacharow found a bacillus 0.25μ to 1.5μ long and Tokishige a very small short bacillus the cultures of which produced rinderpest in cattle. It would seem as if here as in the case of lung plague, the experimenters had retained the real but invisible pathogenic agent in what they took for pure cultures. Semmer attributes the disease to fine corpuscles which have so far eluded current methods of staining and cultivation, and that they exist in the number of from one to six in the enlarged cell nucleus. Nicolle and Adel Bey sustain this position, having found that the unseen virulent germ passed through the more open and thinner Berkefeld filter, but failed to traverse the denser Berkefeld and Chamberland porcelain filters even when favored by a somewhat higher temperature. As this filtration usually removes the germ and renders the liquid noninfecting they hold that the real germ is almost certainly intraleucocytic. When in exceptional cases a few pass through the filter it is held to be only such as were free in the liquid, and these are usually so small in number, that inoculation with the filtrate does not kill, nor always produce appreciable symptoms, but only immunity.
Accessory Causes. The essential cause being the germ, accessory causes are of necessity such as contribute to the preservation of that microbe and its introduction into the systems of susceptible animals.
Susceptibility has a powerful influence even in races habitually subject to rinderpest. The highest susceptibility inheres in cattle, and yet the surviving cattle of the Steppe race, which has been exposed to the infection for centuries, mostly recover from the plague, while fresh cattle imported into the Steppes perish almost without exception. Sheep and goats contract the disease but it is more severe and deadly in the latter than in the former animal. Both, however, can carry the infection back to the bovine animal, as can also the whole group of ruminants. The Guinea pig contracts the affection by inoculation and may thus become an indirect means of conveying infection from ox to ox.
Immunity follows a first attack. Calves born of cows that passed through cattle plague during the last months of gestation are usually immune.
Exposure to infection arises in various ways. All of the secretions of the diseased animal are apparently infecting, and the virus possesses great vitality, so that the channels of infection are almost endless. It is carried in the manure, washed on in streams, and drains, dried up on hay, straw, feathers and other light objects, or in dust, and blown about by the winds, left in stables, in feeding and watering troughs, in railroad cars, steamboats, ferry boats, loading banks and yards, it is carried in the fresh milk, flesh, fat, sausage cases, hairs, hoofs, horns, wool and bristles, in hides and bones, in halters and harness, on wagon shafts and poles, on goads, on boots and clothes of men, and the feet of dogs, birds and other animals, on the wheels of vehicles, the runners of sleighs, and by vermin and wild animals. The various infected products, however, soon lose their virulence after drying. Galtier assures us on the basis of the experiments of a Russian Commission, and the experience of France, Belgium, England and other countries that dried or salted hides can be introduced with perfect safety, and that rendered suet, and dried skins, horns, bones and hairs are equally harmless. On stalls, mangers and racks on the other hand, in an obscure and still atmosphere, virulence may be preserved for three months (Müller, Dieckerhoff). Again in litter and manure in the open air, and even in yards and pastures it may retain its vitality for weeks (Chauveau). The infection is destroyed by a temperature of zero, or 131° F. (Semmer).
Whatever determines a movement of animals from an infected locality, determines the extension of the plague, hence war, and commerce, the food demands of a large and encreasing manufacturing population, the inauguration of new routes of rapid transit by steam over land or sea all contribute in their various ways to the extension of rinderpest.
Lesions. The most significant feature of the morbid lesions is their concentration on the fourth stomach, small intestine, rectum, oral cavity and vagina. The respiratory apparatus, eyes, skin, muscles, and nervous system suffer to a lesser extent. If the case has gone on to a fatal result there is usually marked emaciation, the natural openings (mouth, nose, eyes, anus) are soiled with morbid discharges (muco-purulent, feculent) the thighs smeared with offensive liquid fæces, and the skin may be yellowish red, or dark, with a general scurfy condition and distinct eruptions, especially of rounded wart-like epidermic concretions on teats and udder. The eyes are deeply sunken, the conjunctiva of a yellowish red, and the lips and muzzle dry, swollen and it may be eroded.
The buccal mucosa is swollen, fœtid, with marked epithelial desquamation and more or less deep and extended erosions on the upper and lower lips, gums, dental pad of the upper jaw, cheeks, hard palate, and root of the tongue. There may still be some of the characteristic, white, epithelial concretions, or the epithelium may hang in loose semi-detached shreds, or there may be extensive areas of abrasion, in transverse cracks or broad patches, and finally extensive petechiæ. The conical papillæ on the cheeks and dorsum of the tongue are especially liable to dark red petechial discolorations.
The subderma and submucosa are also suffused with these congestions and petechiæ, and like the epidermic layer show a marked increase of all elements and of the cell nuclei.
The congestions, petechiæ, desquamations, erosions, are found on the fauces, pharynx, gullet, nasal mucosa, trachea, and bronchia, to a greater or less extent in different cases. There may be even limited areas of superficial necrosis and even the formation of false membranes. In the diseased epidermis and epithelium, in the necrotic plaques and false membranes there are spores and mycelia of fungi and bacterial growths.