Pathomorphological and immunohistochemical investigations of myelocytoma caused by avian leukosis virus-J in adult laying birds

The subgroup J of avian leukosis virus causes myelocytomas, a neoplastic condition of the birds that affects several visceral organs. In the present study, myelocytomas were diagnosed in adult laying birds based on cytological and histopathological examination. On necropsy examination, the birds showed enlarged liver and spleen with multifocal tumorous growths in liver, spleen, kidneys, lungs, ovary, proventriculus, intestine and mesentery. Cytological examination of the impression smears from tumorous lesions revealed the characteristic myeloid cell population with granular cytoplasm and large eccentric nucleus with prominent nucleoli. Histopathologically, most of the organs showed infiltration of uniform sized, large myeloid cells arranged in sheets or columns. These cells had large number of cytoplasmic acidophilic granules and pleomorphic, vesicular or lobulated nucleus with few chromatin clumps. In addition, mitotic figures were also observed. The confirmatory diagnosis was done by immunolocalization of ALV-J viral antigen within the infiltrating cells in various tissues. Thus, the present study revealed circulation of ALV-J in the adult laying birds causing myelocytomoa under field conditions in Punjab, India. Further, cytopathology can be used as an alternative tool for diagnosis of this viral disease in field conditions with limited resources.