INFECTIOUS DISEASES 175 



danger in the community. The cholera-infected swine 

 are hauled or driven from the farm to the railroad station 

 along or over the public road, which thus becomes a 

 source of infection, the virus of which may collect on the 

 feet of horses, on the wheels of wagons or other vehicles, 

 and be transported to farms where infection had not 

 before been present. 



The possibility of virus carriers of hog-cholera infec- 

 tion must be admitted, for such carriers and distributers of 

 infection are recognized in other infective diseases. It 

 has been claimed by good authorities that swine immun- 

 ized simultaneously do not eliminate the virus, but this 

 claim has not been satisfactorily proved, and because of 

 the possibility of such swine eliminating infection, they 

 must be considered a source of infection. 



Dogs, crows, buzzards, and pigeons are scavengers, and 

 are an important factor in the dissemination of infection. 

 Neighbors visiting back and forth and exchanging labor 

 are prolific means of carrying infection from place to 

 place. And careless veterinarians have in some instances 

 apparently been responsible for the transmission of hog 

 cholera from infected to non-infected premises. 



Manner of infection. Hog cholera may be trans- 

 mitted by direct or indirect infection. Direct infection 

 may be affected by the actual contact of a healthy, 

 susceptible swine with one affected with cholera. Direct 

 infection may also occur in utero, the pigs becoming 

 infected before birth. This statement may be questioned 

 by some, but the fact that pregnant sows abort when they 

 become affected with hog cholera is common knowledge 

 among swine breeders. It has also been observed that 

 abortion is of frequent occurrence in pregnant sows that 

 are simultaneously immunized. The transmission of the 

 virus from the sow to the pig in utero would not seem 

 difficult when it is remembered that this virus readily 

 passes through porcelain filters. 



Indirect infection also is of common occurrence in 

 hog cholera. This is accomplished by the infection being 

 introduced on food stuff, in water, in the inspired air, or 



