Phylogenetic analysis of avian retroviruses with neuropathogenicity in central nervous system

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Avian leukosis virus (ALV) mainly causes hematopoietic neoplasms in chicken, whereas fowl glioma-inducing virus (FGV), which belongs to ALV subgroup A, induces astrocytoma in chickens. Fowls kept in zoological garden A in Toyama have been considered as source for the FGV infection in other Japanese zoological gardens. However, the background and process how FGV acquired the unique oncogenicity in nervous system has not been clarified. At first, to detect FGV using nested PCR, primers were designed specific to the 3' untranslated region (UTR) and the PCR-protocol was established. The prevalence of FGV by the nested PCR in 131 Japanese fowls of zoological garden A was 40% and the prevalences in a total of 129 chickens in three other zoological gardens, which were received the eggs or chicks from the zoological garden A, were 26 to 56%. Phylogenetic analysis revealed that 3' UTRs, including the FGV-specific sequence, of the 14 isolated ALVs showed high sequence identity and a close relati … More onship with that of FGV. Secondly, the prevalence in chickens, which were not related by birth to any fowls of the zoological garden A, was examined. Ancestors of Japanese fowl are thought to be brought to Japan in the Edo era from Southeast Asia. Along the propagation path, feather pulps and cloaca swab were collected from 264 chickens in Indonesia, Philippines, South Korea and Japan. Twenty nine chickens, including 9 birds in the foreign countries, were positive for nested PCR and the amplified products of showed 98% nucleotide sequence homology to the corresponding region of FGV. Six strains of FGV were isolated from these chickens in Japan. On the other hand, different ALV strain (Tyms_90) was isolated from brains of layers affected with fowl glioma and subcutaneous mesenchymal neoplasm in Japan. Another two Japanese fowls in Japan showed perineurioma and neurofibroma, respectively and a strain of ALV having endogenous-1(ev-1) locus was isolated from the latter. These results suggest that mutants of FGV spread in Japanese fowls in Japan, that small number of domestic and foreign chickens unrelated to the birds in the zoological garden A is infected with FGV, and that Japanese fowls are infected with other ALVs having ev-1 locus in the genome and showing oncogenicity in nervous system. In conclusion, it is speculated that FGV has appeared outside of the zoological garden A and a part of FGV-infected chickens were brought to this garden and used for breeding. Less