362 ACUTE GENERAL INFECTIOUS DISEASES 



when the food is changed. Hog-cholera, however, commonly 

 breaks out among swine fed kitchen ofPal from large institu- 

 tions (penitentiaries, asylums). The food in these cases is 

 not the cause. Large numbers of hogs are bought up indis- 

 criminately to consiune this waste, and with them a few 

 which either have cholera in a chronic form or are cholera 

 convalescents ("virus carriers")- 



(b) Tuberculosis. — ^This is a common disease of swine which 

 follow tubercular cattle, or are fed skimmed milk containing 

 tubercle bacilli, or the tubercular offal from slaughter houses. 

 It would be confused only with chronic cholera. The history 

 and necropsy nearly always suffice to differentiate between 

 the two diseases. In cases of doubt the bacteriological 

 examination (staining for tubercle bacilli) may be employed. 



(c) Lung Worms (Strongylus paradoxus). — ^These thread 

 worms are sometimes found in the bronchi of young pigs. 

 They induce chronic cough and general unthriftiness. Occa- 

 sionally death is induced through pulmonary edema. A 

 necropsy reveals absence of cholera lesions and the presence 

 of the strongylus in the foamy mucus of the small bronchi. 



(d) Swine Plague. — In the field the differentiation between 

 swine plague and hog-cholera is most difficult and sometimes 

 impossible. Swine plague appears sporadically and tends 

 to disappear suddenly in a herd. Hog-cholera is epizootic 

 and usually passes through the whole herd. It must be borne 

 in mind, however, that the two diseases may coexist. On 

 necropsy the characteristic changes of swine plague are either 

 fibrinous or necrotic pleuropneumonia, acute swelling and 

 hemorrhages in the lymph glands. In hog-cholera the char- 

 acteristic lesions are noted in the bowels (diphtheritic enteri- 

 tis, "button ulcers"). An accurate differentiation can be 

 made only by filtering the blood and injecting susceptible 

 animals. Negative results from filtration experiments, 

 however, do not disprove the existence of hog-cholera as the 

 virus may have been eliminated from the body before the 

 inoculation material was collected. On the other hand the 

 presence of the bipoled organism in the blood and tissues is 

 not absolute proof of the presence of swine plague, as these 

 organisms have been found in the absence thereof. 



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