THE CHARACTERISTIC OF SO-CALLED FOWL GLIOMA, WHICH IS A UNIQUE CENTRAL NERVOUS SYSTEM NEOPLASM IN ANIMALS CAUSED BY A RETROVIRUS

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So-called fowl glioma is characterized by multiple nodular gliomatous growths associated with disseminated nonsuppurative encephalitis. The causal agent is still unknown. The purpose of the present study was to examine the relationship between so-called fowl glioma and an avian leukosis virus (ALV) as the causative candidate. One-day-old chicks of Japanese bantams and specific pathogen-free (SPF) chickens were intracerebrally inoculated with the brain homogenate or culture supernatant from the affected bantam. Most of birds in the inoculated roups showed nonsuppurative encephalitis, and the 18 bantams (82%) and five chickens (28%) developed multiple nodules consisting of aggregations of astrocytes in the cerebrum. These astrocytes immunohistochemically had ALV antigen. By Southern blot analysis, the ALV proviral sequence was detected both in DNA from the brains of the inoculated birds and in DNA from the inoculum. Tadpole-shaped particles, approximately 100 nm in diameter, were detected in the inoculum, and budding of the particles was noted on the cell surface of the infeced CEF. The env gene sequence of the DNA from the CEF was most similar (> 92% identity) to the env gene of ALV-B subgroup. Nonsuppurative myocarditis was also observed in the inoculated SPF chickens. The gliomatous nodules at the initial stage ultrastructurally consisted of neoplastic proliferation of astrocytes and mild desmoplastic reaction of the adventitial fibroblasts. Perineurioma-like neoplasm, which were also suspected to be related with the ALV, was rarely observed in the peripheral nerves of the birds. The present study demonstrated that so-called fowl glioma is a viral disease caused by a subgroup A or B of ALV. Our results suggest that the infected birds reveal nonsuppurative encephalitis and myocarditis immediately after the infection and most of these birds develop glioma/gliomesenchymal mixed tumor or peripheral nerve neoplasm since 4 months of age.