The virus of canine distemper in cell culture: II. Effect of serial passage in ferret kidney cell cultures and BS-C-1 cell cultures on the virulence of canine distemper virus

Abstract

Passage of virulent canine distemper virus in ferret kidney cell culture produced little attenuation for ferrets. Virus passaged 8 times in BS-C-1 cell, although producing clinical signs of distemper did not kill 3 3 ferrets. After 21 serial passages in BS-C-1 cells, the virus was modified so that it failed to produce distemper in 8 8 ferrets and only a mild temperature response in 5 5 puppies. Furthermore, the animals were protected against challenge with virulent CDV which killed 10 10 ferrets and produced clinical distemper in 7 7 puppies. These results are highly significant. The BS-C-1 adapted CDV was retested after it had been purified twice by cloning under agar overlay, and at the 37th passage level protected dogs and ferrets. About 10 infective doses of attenuated virus induced active immunity in ferrets: a thousand times this dose produced no signs of clinical distemper in ferrets, and only a mild temperature response in dogs.