Retroviral particles in neoplasms of Burmese pythons (Python molurus bivittatus)

Neoplastic diseases associated with retroviruses were diagnosed in four Bur mese pythons (Python molurus bivattatus) from a single collection. Snake No . 1 was a 7-year-old female with recurrent undifferentiated mesenchymal rou nd cell tumor (lymphosarcoma) of the oral cavity. At necropsy, similar neop lastic masses were evident in the uterus and ovary, and there was diffuse i nvolvement of the spleen. Snake No. 2 was a 4.5-year-old female that was eu thanatized because of complications following resection of a segmental colo nic adenocarcinoma. Snake No. 3 was a 5-year-old female that was euthanatiz ed because of a large transitional cell carcinoma of the right kidney. Snak e No. 4 was a 19-year-old female that was euthanatized following recurrence of an intermandibular fibrosarcoma. Ultrastructural examination revealed f ew to numerous extracellular and intracellular (intravacuolar) type C-like retroviral particles in all tumors. Tumors were about 90-95 nm in diameter, with an electron-dense core and bilaminar external membrane. The relations hip of the intraneoplastic viral particles to the etiology of the tumors is uncertain.