Pathogenicity of field isolants of hemagglutinating encephalomyelitis virus for neonatal pigs.

The pathogenicity of hemagglutinating encephalomyelitis virus isolated from the brain of each of 5 pigs with clinical signs and microscopic lesions of encephalomyelitis (1 pig from each of 5 naturally infected herbs) was tested under experimental conditions. Each isolant was administered intranasally to 5 neonatal pigs. Clinically affected pigs developed either an acute or chronic form of illness, commencing 4 to 8 days after exposure. Listless, inappetence, and vomiting were clinical signs common to both forms. Additional signs of the acute form were paddling, muscle tremors, and hyperesthesia. Additional signs of the chronic form were loss of condition and either loss of weight or failure to gain weight at a rate similar to nonaffected littermates.