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Virus Content of Shope Papillomas of Cottontail Rabbits¹

Department of Microbiology, School of Medicine, University of Washington, Seattle, Washington 98105

The virus content of naturally occurring and experimentally induced papillomas of cottontail rabbits varies considerably. As a rule different individual papillomas on the same rabbit were found to have a similar virus content. The amount of virus usually increased as the tumors aged from 6 to 12 weeks. After 12 weeks there was no consistent pattern of change in virus content of papillomas, and dilution end points of 10^-3 to 10^-5 were commonly observed for at least 1 year. Tumors with low and intermediate levels of virus were induced by inoculation of 500 ID₅₀ and by 0.5 ID₅₀ of the same virus suspension. The white avascular portions of papillomas from the 2 cottontail rabbits tested were found to contain a substantially higher amount of virus than the dark portions of the same tumors. Papillomas tested several weeks before regression had a high virus content. Virus persisted in considerable amounts in these tumors during the entire period of regression.

¹ This investigation was supported in part by Research Grants CA 02668 and CA-5040 from the National Cancer Institute, NIH, USPHS.

Received 9/19/66. Accepted 1/11/67.