EVOLUTIONARY CHANGES IN MYXOMA VIRUS IN BRITAIN. AN EXAMINATION OF 222 NATURALLY OCCURRING STRAINS OBTAINED FROM 80 COUNTIES DURING THE PERIOD OCTOBER-NOVEMBER 1962.

Abstract

Samples of lesions containing viable myxoma virus were collected from 222 infected wild rabbits captured in 80 counties of Britain during October–November 1962. They were dispatched by air to Australia and passaged once in domestic rabbits before being tested for their virulence by the intradermal inoculation of groups of six laboratory rabbits with small doses of virus.The results showed that a wide range of viruses of differing properties now coexist in Britain. Their virulence ranges from very high (99 % lethal) to low (about 50 %), but the majority of strains fall into the grade III virulence group, with estimated case mortality rates varying between 70 and 95%. The viruses also produce disease of varying symptomatology, skin lesions being very prominent, raised or flat. There was no obvious association between lesion type and virulence.Tests made on the wild rabbits from which the samples were obtained, and on Inoculated domestic rabbits, showed that virulence could not be predicted by gel-diffusion tests.