Observations on a naturally occurring winter epizootic of myxomatosis at Canberra, Australia, in the presence of rabbit fleas (Spilopsyllus cuniculi Dale) and virulent myxoma virus.
A rabbit from a colony of 143 adult rabbits kept in a rabbit-proof 32-hectare paddock was inoculated with the virulent Lausanne strain of myxoma virus, infested with 25 S. cuniculi, and returned to the colony. It first showed clinical signs 7 days later. However, on the day after it was released, another rabbit in the colony was found to have myxomatosis caused by a field strain. During the outbreak, 70% of the adult rabbits contracted the field strain, 11% the Lausanne strain, and 13% an indeterminate strain. Only five adults, all of which contracted the field strain, survived. The mean duration of clinical symptoms in adult rabbits was 9.3 days for the field strain and 3.4 days for the Lausanne strain. As the course of the outbreak was very similar to one caused by a field strain two years previously in the same paddock, it was concluded that the course was not affected either by the presence of fleas or by the release of virulent myxoma virus, both of which were absent in the previous outbreak. It appears that the transmission of myxomatosis among rabbits infested with both S. cuniculi and Listrophorus gibbus (a mite) is not significantly different from that among rabbits infested with L. gibbus alone.