Histopathogenesis of Porcine Polioencephalomyelitis in the Germ Free Pig

Twenty-four germ free pigs were used to study the disease produced by oral inoculation of a porcine polioencephalomyelitis virus. Fever and diarrhea were noted in all pigs after the seventh post-inoculation day; neurological signs were generally mild. Lesions of polioencephalomyelitis occurred in all pigs killed 7 or more days following inoculation. The initial lesions were those of neuronal degeneration. Perivascular cuffing, cellular infiltrations, and neuronophagia were most marked 10 to 14 days following inoculation. The spinal cord and associated dorsal root ganglia were the sites of most severe lesions. A decreasing frequency of lesions was apparent in anterior areas of the brain stem. Changes in the cerebellum and rhinencephalon were sparse and they were rare in the cerebral cortex. Lesions in the adrenal gland were noted during the initial stages of virus infection and suggested a possible extraneural site of virus multiplication. The pathogenesis of central nervous system infection was discussed and the blood vascular system was favored as the portal of viral entry.