Studies on Adaptation of Rous Sarcoma Virus to Ducks.

Normal, chick embryonic tissues were mixed with Rous sarcoma virus and inocu lated into 1-day-old ducklings and conditioned hamsters. In the hamsters tumors, although small, grew, and a high titer virus was demonstrated. In ducklings there were temporary growths followed by rapid regression. When the ducklings were treated with large doses of cortisone and infected with the high titer virus, a progressive growth of the tumor was observed. A tumor grown in a cortisone-treated duckling and extirpated on the 7th day was still a chicken-type, and the tumor extract induced sarcoma in chickens but not in ducklings. However, once passed through condi tioned hamsters, together with normal chick embryo, a duck-adapted variant virus was isolated. On the other hand, when another tumor in cortisone-treated ducklings was ex amined on the 14th day, signs of adaptation of Rous virus were evident. The variant virus thus obtained was oncogenic in 8-day-old or older ducks and at the same time retained oncogenicity in chickens.