A non-winter epizootic of myxomatosis in subalpine south-eastern Australia

A myxomatosis epizootic, that occurred in February-April 1972 in a rabbit population in which a winter epizootic was observed in 1969, is described. Rabbit fleas had been introduced into the rabbit population in the intervening period. In the 1972 outbreak the case mortality was only 33% compared with 86% in 1969. The difference is thought to be related to the colder conditions during the 1969 epizootic. The morbidity rate could not be accurately measured in 1972 but was a minimum of 65%. It is believed that in the 1972 epizootic the virus was transmitted by rabbit fleas. It appears that any change in the epidemiological pattern of myxomatosis towards summer epizootics in areas in which they have previously occurred in winter will drastically reduce the rabbit mortality currently caused by myxomatosis. The introduction of rabbit fleas may increase the likelihood of epizootics in summer and autumn.