Stvine Groiuers' Association. 299 



HOW THE INFECTION IS PROPAGATED AND SPREAD. 



A knowledge of the ways in which the infection is propagated 

 and spread is essential to the application of rational methods of 

 control of hog cholera. Every infectious disease is due to a spe- 

 cific cause, in the nature of a parasitic micro-organism, which 

 lives and multiplies for a time in the body of the hog that suffers 

 from a disease. In hog cholera the exact nature of this germ 

 has not been determined. These facts, however, have been estab- 

 lished : The micro-organism exists in a virulent form in the blood, 

 and organs of the body, and in the excretions of the sick animal. 

 This hrs been proven by feeding and inoculation experiments on 

 susceptible hogs. The urine and dung of the sick animals retain their 

 virulence for a considerable time after passing from the animal; 

 as shown by the fact that susceptible animals, when put in pens 

 previously occupied by sick hogs, contract the disease. The dung 

 and urine of sick hogs, and the carcasses of hogs that have died 

 of cholera, are the usual sources of infection from which fresh 

 outbreaks of cholera originate. There are a variety of ways in 

 which the disease is carried from a focus of infection. The pigs 

 from a healthy herd often become infected from a diseased herd 

 of an adjoining farm by breaking through insecure division fences 

 and carry the disease to the home herd. A sufficient amount of 

 infectious dung may be carried on the shoes of a person, who has 



walked about in a pen containing diseased hogs, to start the dis- 

 ease in a healthy herd. Dogs may also carry the infection from 

 one farm to another on the feet, or by carrying home a portion of 

 a diseased carcass, which had not been properly disposed of. 

 Barnyard fowls often spread the disease quickly over the farm 

 from the first infected pen. Pigeons and crows, after feeding 

 among diseased hogs, may carry the infection to the feeding lots 

 of a neighboring farm. The litter and dung from infected pens, 

 or portions of a decaying carcass, may be carried a long distance 

 by the natural streams, or by drainage following heavy rains. 

 During outbreaks of cholera, it is the custom of farmers to put on 

 the market the healthy looking hogs from a diseased herd. Some 

 of these apparently healthy hogs are, in fact, infected with the 

 disease ; and all of them carry at least a small amount of infectious 

 material on their feet and bodies. If such animals are driven to 

 the shipping station, as often happens, some disease producing 

 material is dropped on the public highways to be picked up by the 

 pigs of abutting farms. The small streams that run across the 



