Diseases of cattle, sheep, goats and swine

by G. Moussu; Jno. A. W. Dollar

Etiology. As regards the etiology of the form of swine fever prevalent in England no question now exists. It has been proved to demonstration by the bacteriological inquiry conducted by Professor McFadyean that it is due to a special pathogenic organism, a bacillus, which, after cultivation in artificial media, will produce in the healthy pig fed with the pure cultures the typical ulcerations which are found in the intestines of pigs affected with swine fever contracted in the ordinary way.

The observations made by the veterinary officers of the Board of Agriculture caused them to doubt whether there was any disease of the lungs of pigs which, in the absence of lesions in the intestinal tract, could be accepted as evidence of swine fever.

The bacillus which produced swine fever when introduced in the healthy pig did not induce any special disease of the lungs.

Pathology and morbid anatomy. Swine fever, like typhoid fever in man, is essentially a disease of the digestive system, its chief characteristic being certain morbid changes of a well-marked nature which are found upon the surface of the mucous membrane in some part of the alimentary canal.

The changes referred to consist of what have been commonly described as the formation of a series of ulcers, single or confluent, distributed upon some part of the intestinal tract, varying in size and shape, of a yellowish-grey to black colour, and assuming as a rule a circular form. In some instances the lesions consist of diphtheritic exudations with necrosis of the lining membrane of the bowels.

These ulcers or necrotic patches may be found upon the tongue, tonsils, epiglottis, stomach, and small intestines, but they are more constant in the large intestines, especially the cæcum and colon. The lesions may involve the whole thickness of the mucous membrane, but seldom penetrate the other coats of the intestine; in fact, perforation of the peritoneal covering of the bowel is very rare in even prolonged cases of swine fever.

In cases where swine fever assumes the more acute form and death supervenes rapidly, it is usual to find that the small intestines are largely involved.

In the non-acute or slowly progressing form the lesions are more abundant in the large intestines, and in some instances the walls of the intestines become so thick as a result of infiltration into their structure and the excessively thick deposits upon the lining membrane, that it becomes a matter of surprise that the passage of the ingesta has been possible and that the animal has lived so long.

Next to the intestinal lesions the congested condition of the lymphatic glands, especially those of the mesentery, may be considered as most prominent among the pathological changes which occur in swine fever. Occasionally centres of necrosis are observed in the liver, and some writers refer to changes in or upon the spleen and kidneys.

The only lesions which can be characterised as absolutely typical of swine fever are those present in the bowels, the absence of which will justify any observer in declining to accept the case as one of swine fever without some further evidence or inquiry. It must, however, be distinctly understood that in the case of very young pigs which have died shortly after infection, there is often an entire absence of the lesions described, the only changes present being inflammation of the stomach or some part of the intestines.