LECTURE LII. 

 HOG CHOLERA, AND SWINE PLAGUE. 



Definition. — It is evident that there are at least three distinct 

 diseases of swine which are commonly confused under the name 

 of hog cholera. These are true hog cholera, swine plague, and 

 swill-barrel cholera. Most of the outbreaks of infectious disease, 

 under this name are mixed infections of hog cholera and swine 

 plague. 



Very few typical cases of either swine plague or hog cholera 

 alone are seen. 



It is undoubtedly possible to have an unmixed outbreak of 

 either hog cholera or swine plague, although the existence of epi- 

 demics of swine plague unmixed with hog cholera has not been 

 clearly proven. Unmixed infection from hog cholera in which 

 no swine plague lesions appear is probably more common. It is 

 a matter of some importance for farmers and stockmen to know 

 which disease they have to deal with, or whether there is mixetl 

 infection, for while these diseases are equally contagious, and 

 equally fatal, the swine plague germs are much more easily de- 

 stroyed, and this disease is much more easily controlled than is 

 hog cholera. 



Variations in virulence.— Different outbreaks of so-called hog 

 cholera vary greatly in virulence. In some epidemics the infec- 

 tion is marked, and the hogs die quickly ; in other epidemics the 

 majority of the cases assume the chronic type ; the hogs do not 

 die so quickly, and the percentage of loss is not so great. 



Various gradations may appear between epidemics of the ut- 

 most virulence and those of the milder type. 



Two factors are to be considered in explaining this variation. 

 It has been shown that there are at least six varieties of the hog 

 cholera bacillus which differ somewhat in the virulence of the 

 disease they produce, and that each one of these varieties, under 

 uniform conditions, will produce a certain type of hog cholera. 



