446 HORSE, SWINE AND POULTRY DISEASES 

 CONTAGIOUS AND INFECTIOUS DISEASES. 



HOG CHOLERA. 



Description. Hog cholera is an acute febrile disease which, so 

 far as is known, affects only hogs, and which is characterized by ex- 

 treme contagiousness and a very high death rate. It is usual to 

 speak of two forms of this disease. One is called the acute and the 

 other the chronic form. This is because of the fact that in some 

 cases the disease is sudden in its onset and rapid in its course, where- 

 as in others the affected hogs linger for weeks or months before death 

 or recovery. Notwithstanding the dissimilarity in the symptoms and 

 lesions observed in these two types of hog cholera, the causative 

 agent is the same in both, the difference in the manifestations of the 

 disease being no doubt due to a variation in the virulence of the 

 germs which cause the disease, and possibly to some extent also to a 

 variation in the resisting power of hogs. 



Prevalence. Hog cholera is found in practically all parts of the 

 world, and is especially prevalent in the large hog-raising districts of 

 the United States. The first recorded outbreak in this country oc- 

 curred in the year 1833 in the State of Ohio, and is supposed to have 

 arisen through the importation of hogs from European countries, 

 where the disease, no doubt, existed prior to its appearance in this 

 country. From the original center of infection the disease has grad- 

 ually extended to all portions of the United States, the spread being 

 usually along the lines of transportation. Owing to the former lim- 

 ited facilities for communication between the Eastern and the Pacific 

 Coast States, the latter section remained free of this disease until 

 within the last few years, but reports received recently show that the 

 disease now exists there, and at the present time no section of the 

 United States may be regarded as free from hog cholera. Enormous 

 losses are caused yearly in the large hog-raising States of the Middle 

 West, and it may be safely said that several of these States lose 

 yearly an average of more than $1,000,000 each from this source 

 alone. While outbreaks may occur at all seasons of the year, the 

 great majority take place during the late summer and fall. The 

 mortality from hog cholera is as high as 100 per cent in some herds, 

 while the average is probably from 70 to 80 per cent, and many of 

 the hogs which survive are comparatively worthless, owing to their 

 being weakened and stunted in growth. (F. B. 379.) 



Cause of Hog Cholera. The germ or microbe which causes hog 

 cholera is present in the blood of sick hogs and also in the excretions 

 from such hogs, particularly in the urine. It has been shown that 

 the disease can be produced almost without fail by inoculating well 

 hogs with the blood or urine from sick hogs. The germ which is in 

 this blood and urine is so small, or else of such structure, that it can 

 not be seen with the strongest microscopes now available. It has 

 never been cultivated in laboratories, as has been done with many 

 other infectious germs, and we know of it only by the effects which 

 it produces. The germ of hog cholera is therefore classed with the 

 "invisible micro-organisms," and in this respect it resembles those 

 which bring about a number of other diseases of animals and men, 



