148 REPORT OF THE BUREAU OF ANIMAL INDUSTRY. 



PREVENTION OF HOG CHOLERA.* 



ISOLATION, DISINFECTION, AND CLEANLINESS AS PREVENTIVE MEAS- 

 URES. 



It is frequently necessary to apply preventive measures before in- 

 fectious diseases have actually appeared in a herd. The disease may 

 have appeared on a neighboring farm and the problem then arises, 

 How can the disease be prevented from spreading to other farms ? 

 How can the surrounding farms keep the disease from their premises ? 



The sources and channels of infection are as follows, the most com- 

 mon and important being placed first: 



(a) Pigs purchased from infected herds, or coming in contact with those from 

 infected farms, or running over ground occupied by diseased swine within a period 

 of two or three months. 



(6) Infected streams may communicate the disease to herds below the source of 

 infection. 



(c) Virus may be carried in feed, implements, and on the feet and clothing of per- 

 sons from inf ected herds and premises. 



(d) Winds, insects, birds (particularly buzzards), and various animals may trans- 

 port hog cholera virus. 



(a) In regard to a, it may be said that no pigs should be purchased 

 from any locality until one year after the death of the last case of 

 cholera. There are frequently, near the end of an .epizootic, chronic 

 cases which may live for three or four months without showing any 

 distinctive signs of disease until they suddenly die. The post mortem 

 examination usually reveals extensive \ilceration of the large intes- 

 tine. The disease may thus linger in a herd long after all danger 

 has apparently subsided. By bringing any chronic cases in contact 

 with hitherto unexposed healthy swine the disease may spring up 

 anew, as a dying fire would among fresh fuel. Although our exper- 

 iments have shown that the disease germs may all disappear from 

 the soil in three or four months, the uncertainty of knowing 

 whether there are any chronic cases continually adding fresh virus 

 to the soil makes the period of one year not too long. It is advisable, 

 in districts where hog cholera is very prevalent and is rarely absent 

 for any length of time, for farmers to raise their own pigs and not 

 trust to any animals from outside. In this way infection may be at 

 least in part kept under control. When animals have been obtained 

 from places which are not above suspicion, they should not be brought 

 in contact with swine already on the place, but quarantined as far as 

 possible from them and kept under careful observation for at least 

 one month. 



(b) Perhaps the most potent agents in the distribution of hog 

 cholera are streams. They may become infected with the specific 

 germs when sick animals are permitted to go into them, when dead 

 animals or any part of them are thrown into the water, or when pig 

 pens are drained into them. They may even multiply when the 

 water is contaminated with fecal discharges or other organic matter. 

 Experiments in the laboratory f have demonstrated that hog cholera 

 bacilli may remain alive in water for four months. Making all due 

 allowance for external influences and competition with other bacteria 



* Equally applicable to swine plague. f See bulletin on hog cholera. 



