612 INFECTIOUS DISEASES 



Etiology.— This disease is produced by a specific virus, 

 the nature of which has not been determined. All animals 

 except fowls are susceptible to inoculations with the virus 

 which is found in the blood, central nervous system, and 

 in some of the other tissues. The saliva, bile and urine are 

 free from the virus. 



Pathogenicity.— Most animals are very susceptible to 

 infection by inoculating them with only minute quantities 

 of the blood, or central nerve tissues, from those affected 

 with the disease. At the point of inoculation, the tissues 

 become red and inflamed; later, necrotic. The inoculated 

 wound shows intense irritation, and the animal bites and 

 scratches the part almost continuously. Dogs and cats 

 contract the disease readily after being fed on organs or 

 tissues containing the virus. 



Natural Infection.— This has not been definitely established, 

 but probably in most cases is due to eating infected meats, 

 or being inoculated by infected mice or rats. 



Pathology.— No marked lesions are found in this disease, 

 except at the point of inoculation. The meninges of the 

 brain, and the brain substance, usually show hyperemia, 

 and blood extravasations. AVhen infection takes place in 

 cats and dogs from eating infected meat, the stomach and 

 small intestines are congested, and in some cases markedly 

 inflamed. Hemorrhages under the mucosa, and frequently 

 petechias on the serous membranes of the stomach and intes- 

 tines are noted. No other lesions are found. 



Symptoms.— The period of incubation varies from two to 

 nine days. The onset of the disease is characterized in the 

 dog and cat by a sudden change in disposition, tendency to 

 seek dark, cool places, where the patient lies quietly or 

 maintains a crouching attitude. They often cry or mew 

 as if in severe pain. Vomiting is more or less persistent, 

 there is complete loss of appetite, and marked salivation. 

 Severe itching is manifested in niost cases by the animal 

 scratching and biting itself, sometimes so severely that the 

 skin is entirely removed over the involved area, usually 

 around the lips or face. In some few cases this symptom may 



