276 SWIKE PRACTICE 



are apparently due to a primarj' infection with either the B. suipesti- 

 fer, B. suisepticus, B. coli communis, enteritidis and possibly some 

 other microbian agents separately or in various combinations., thus 

 diminishing the resistance of the swine and the virus used in the 

 simultaneous immunization, which under normal conditions would 

 be harmless, actually producing fatal hog cholera. Similar conditions 

 have arisen when swine affected with infectious necrotic enteritis 

 or swine plague have been simultaneously immunized on farms. 



Other predisposing causes of hog cholera are : Age : young animals 

 generally speaking are more subject to hog cholera than mature 

 swine. Sex: excepting mature boars, either sex or barrows are 

 equally susceptible to hog cholera. Old boars may not become af- 

 fected on farms where practically all other swine die of hog cholera. 

 Breed : all breeds of swine are equally subject to hog cholera. The 

 mule foot hog has been claimed to be relatively immune to hog cholera 

 but these claims are not justifiable. Pure-bred and cross-bred swine 

 as well as scrubs and razor backs, all contract cholera. Season: 

 Cholera prevails throughout the year, although it may be m^ore pre- 

 valent in the spring and fall, probably because in those seasons the 

 pigs are at the most susceptible age. Condition of pens: Swine 

 maintained in filthy pens are not so resistant to hog cholera, other 

 things equal, as are swine kept in clean sanitary quarters. Water 

 and feed: Swine are more likely to be healthy if supplied clean 

 wholesome water and feed than if required to drink stagnant filthy 

 water and consume musty or spoiled foods and, therefore, more re- 

 sistant not only to hog cholera but also other diseases. Parasites : 

 Parasites deplete the body and therefore swine infested with para- 

 sites are more susceptible to hog cholera than swine that are free or 

 relatively free, from parasites. Effect of previous disease: Pig scour, 

 navel ill, necrotic stomatitis and other diseases deplete the body and 

 render swine more subject to the action of the filtrable virus. 



Sources of infection. — The original source of the virus of hog 

 cholera like the origin of other viruses and pathogenic agents, is un- 

 known. The following are the principal present " sources of the 

 filtrable virus of hog cholera: Infected swine, the nasal, ocular and 

 fecal discharges and the urine from infected swine, the carcasses of 

 swine dead of cholera, garbage containing scraps of pork, virus used 

 in simultaneous immunization; food, water, vehicles of transporta- 

 tion, stockyards, and other substances or objects that are contami- 

 nated with discharges of infected swine, or the tissues, juices or 



