Histopathological characteristics of spindle-cell proliferative disease in broiler chickens and its experimental reproduction in specific pathogen-free chickens.

The livers and spleens of 45 broiler chickens (33 to 79 days old) suspected of Marek's disease (MD) at meat inspection were collected and examined histopathologically. Macroscopically, they were enlarged from two to three times, and multiple, small, white areas of plaque or infrequent, large, white nodules were observed in most cases. Only 9 birds (20%) were diagnosed with MD based on the histological examination, while the other 35 birds (78%) had tumor-like proliferative lesions in the Glisson's sheath of the liver and in the white pulp and around the sheathed arteries of the spleen, which differs from the pattern seen in MD. The proliferating cells were mainly spindle-shaped or pleomorphic, and were variable in size with abundant eosinophilic cytoplasm. The disease giving rise to the present lesions was diagnosed tentatively as spindle-cell proliferative disease. Total 50 1-day-old specific pathogen-free chicks by serial passage were inoculated intramuscularly with 0.1 ml of a 10% homogenate of the affected livers or spleens. Microscopically, one inoculated bird, necropsied at 6 weeks of age, had spindle-cell proliferative lesions in the spleen similar to the lesions of naturally occurring spindle-cell proliferative disease. Some birds had tumorous lesions, including renal adenoma, leiomyosarcoma and myxosarcoma. Reverse transcriptase-polymerase chain reaction performed using primers specific for subgroup J avian leukosis virus (ALV) produced specific amplifications of subgroup J ALV genes in 4 of 5 field cases examined.