Occurrence of osseous metaplasia in association with Avian lymphoid leukosis - A case report

Lymphoid leukosis is one of the most important lymphoproliferative neoplastic conditions affecting poultry worldwide. The present study reports a very rare occurrence of osseous metaplasia associated with lymphoid leukosis in a flock of layer birds. Carcasses of layer birds brought from an organized farm in the central part of Kerala were used as study material. On necropsy, important gross lesions identified included enlargement of visceral organs especially liver and spleen or formation of discrete whitish nodular tumour-like lesions in various organs. Cytological and histopathological examinations revealed the presence of uniform monomorphic blast cells of lymphoid population in all the affected organs. An unusual observation in these cases was the formation of mature bony trabeculae in spleen. The tissue samples were also subjected to polymerase chain reaction (PCR) and etiology was identified as Avian leukosis A virus. Thus the study revealed the relative potential of the leukosis virus/retro virus to induce osseous metaplasia and heterotopic bone formation. On perusal of literature with special reference to the particular species, similar condition was not found documented and hence, this could be considered as the first case report of osseous metaplasia occurring in association with any lymphoproliferative diseases of poultry. However, extensive studies are required to elucidate the exact pathogenesis of osseous metaplasia in lymphoproliferative diseases of poultry.