482 VETERINARY BACTERIOLOGY 



Distribution. The disease is wide-spread in Europe and North 

 America. 



Nature of Virus. The organism causing hog-cholera is an ultra- 

 microscopic filterable virus. It passes readily through porcelain 

 filters. It has never been cultivated. Fluid material will retain 

 its virulence for a period of ten to fourteen weeks, at least, when 

 kept at room-temperatures. It is killed by exposure ,to 60 to 70 

 for an hour. Desiccation does not destroy it at once, but only 

 after a lapse of several days. It may be destroyed by disinfect- 

 ants, but is relatively resistant. 



Pathogenesis. The subcutaneous injection of 1 to 2 c.c. of 

 filtered blood-serum or body fluids results in the production of the 

 disease. The animals may die of a very acute type of the disease, 

 or it may assume a chronic form. The acute cases generally 

 reveal, on autopsy, hyperemia and acute swelling of the internal 

 organs, and hemorrhages on the serous and mucous membranes, 

 and frequently a serous transudate into the pericardium. In the 

 more chronic type ulcerated and necrotic areas are commonly 

 found in the intestines, together with pneumonia. 



The disease cannot be transferred to other animal species. 

 The Bacillus cholerce suis is probably a secondary invader, but the 

 lesions produced by this organism may in some cases be of the 

 greatest importance. 



Immunity. Animals that have recovered from an infection 

 with hog-cholera are thereafter immune, and it has been shown 

 that their blood has some immunizing power when injected into 

 other susceptible individuals. 



Practical methods of immunization were developed through 

 the work of Dorset, McBryde, and Niles in this country. The 

 method devised by them and commonly used is as follows: It is 

 necessary to start with an animal that has recovered from the 

 disease or that has already been immunized. This animal is then 

 hyperimmunized by repeated injections of virulent blood. The 

 latter must be shown to be virulent by actual test before it can 

 be used. About 1 c.c. of the defibrinated virulent blood is injected 

 for each pound of body weight. A week later an injection of two 

 and one-half times as much is made, and after another week an 

 injection of 5 c.c. Subsequent injections are made, preferably 



