272 INFECTIOUS DISEASES 



Period of Incubation. — The length of time elapsing between 

 the exposure of the hog to the cholera virus, and the development 

 of noticeable symptoms of hog-cholera, varies from a few days 

 to two or three weeks. The length of this incubation period 

 depends on the susceptibility of the animal, the virulence of 

 the virus and the method of exposure. An acute form of hog- 

 cholera indicates a short period of incubation, and a chronic 

 form, a long period. 



Symptoms. — The s_>nnptoms of hog-cholera may differ widely 

 in the different outbreaks of the disease. The symptoms may be 

 classified under the following forms : Acute, subacute and chronic. 

 The acute form of hog-cholera is the most common. The early 

 symptoms are tremors, fever, depressed appearance, marked 

 weakness, staggering gait, constipation and diarrhoea, labored 

 breathing and convulsions. Death may occur within a few hours 

 or a few days. Recovery seldom occurs. In the subacute form, 

 the symptoms are mild and develop slowly. Recovery may take 

 place within a few days, or after extending over a week or ten 

 days it may assume the chronic form. Very often in outbreaks 

 of subacute cholera a large majority of the herd does not show 

 visible symptoms of the disease. In the chronic form, marked 

 symptoms of pleuropneumonia and chronic inflammation of the 

 intestine are common. Ulcers and sores form on the skin and 

 the hair may come off. Large portions of the skin may become 

 gangrenous and slough. This condition is caused by infection 

 with the bacillus necrophorous, and is usually met with in yards 

 that are very insanitary. 



The first symptom of disease is an elevation of body tem- 

 perature. 



At the beginning of any outbreak of hog-cholera the body 

 temperatures of the apparently healthy animals may vary from. 

 105° to 108° F. After a few days, animals that are fatally 

 sick or recovering from the disease may show normal or sub- 

 normal body temperature. 



Loss of appetite is the first s\anptom of disease usually noted 



