Studies in the epidemiology of infectious myxomatosis of rabbits: VII. The virulence of strains of myxoma virus recovered from Australian wild rabbits between 1951 and 1959

Abstract

During the 8½ years, February 1951 to July 1959, 672 strains of myxoma virus were recovered from the field in Australia, all but thirteen, which were derived from mosquito pools, being extracted from the tissues of infected wild rabbits. These were tested for virulence by the intradermal inoculation of small groups of rabbits with a small dose of virus. Based primarily on survival times, strains have been allocated to five grades of virulence, ranging from very high to very low. In spite of inadequate sampling during the first 5 years there has clearly been a trend from a predominance of highly virulent strains in the initial epizootics to a mixture of strains of virulence varying from very high (rarely) to very low. For the last 6 years the proportion of strains allotted to the different virulence grades has remained almost constant, just over half the strains tested each year being classified as moderately virulent.