Seasonal and geographical changes of spontaneous skin papillomas in the Japanese newt Cynops pyrrhogaster.

The occurrence of spontaneous skin papillomas in Japanese newts (Cynops pyrrhogaster) from Niigata prefecture in Northern Japan was monitored over four seasons covering a period of 2 years. Of 13,613 newts, 249 were found to possess papillomas. The percentage of newts with papillomas was highest in autumn, ranging from 1.93 to 5.45% of the total average. These values were more than four times as high as values obtained in the other three seasons (0.16 to 0.50%). A total of 12,167 newts were collected from their natural environment in 10 prefectures of Japan in the autumn of 1980 and 1981. Newts collected from the northern, seaside prefectures had higher papilloma rates (1.00 to 5.45%) than did newts from the Southern, Pacific Ocean prefectures of Japan (0 to 0.27%). Male and female newts were affected equally often by the epitheliomas. Virus-like bodies, resembling herpes-type virus, were found in the cytoplasm of the epitheliomas. These virus-like bodies were not seen in the control epithelium of newts with normal skin and without papilloma or in nonaffected regions of newts with papilloma. It is suggested that tumor and virus are causally related.