278 SWINE PRACTICE 



contaminated and infect healthy, susceptible swine and thus pro- 

 duce hog cholera. Water, too, is frequently the source of infection. 

 This is especially noticeable in the spread of hog cholera in sections , 

 of country in which there are many small streams. Such enzootics 

 usually follow the streams. The contamination of surface water is 

 due to the discharges, and even to the carcasses of cholera-infected 

 hogs being washed by rain into the small streams. j\Iany hog raisers 

 have fenced and made pastures of low lands with small streams of 

 water, thus favoring the introduction of infection into their herds. 



The shipment of cholera infected hogs to market centers has been 

 of common occurrence, althought there is a federal law prohibiting 

 the shipment of swine affected with an infectious disease. By such 

 shipments stockyards, stock cars and the railroad right of way be- 

 come contaminated with discharges of (tholera-infected swine, and 

 the chances are that some of the discharges contain the virus of hog 

 cholera in a sufficiently virulent form to produce cholera in healthy, 

 susceptible swine. By this means cholera is, no doubt, frequently 

 transported hundreds of miles, and new centers of infection pro- 

 duced. 



Federal regulations require the cleaning and disinfecting of cars 

 that are known to have been used to transport cholera-infected hogs 

 to market. This regulation diminishes, the spread of infection, but 

 in some shipments the disease is not' identified until the hogs are 

 slaughtered, and in many instances the cars^ in such shipments are 

 not located and are consequently not cleaned, and disinfected. By 

 the practice of shipping cholera hogs to market, practically all public 

 stockyards become infected and therefore become a source of 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 may adhere to the 

 feet of horses, to the wheels of wagons or other vehicles, and be trans- 

 ported to farms where infection had not before been present. 



The, possibility of virus carriers of hog-cholera infection must be 

 ad^ifldtted, although no definite cases have been identified. It is 

 generally conceded that swine, immunized simultaneously do not 

 eliminate the virus unless they become visibly sick with cholerg, and 

 therefore there is always a possibility of establishing infecited centers 

 by simultaneops immunization. 



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

 portant factors in the dissemination of infection. Neighbors visiting 



