Observations on Myxomatosis in a Rabbit Population With Immune Adults.

Abstract

High mortality (88-100%) was observed during two outbreaks of myxomatosis between 1973 and 1974 in a population of Oryctolagus cuniculus at Canberra. The presence of immune adult rabbits predisposed the disease to be confined either to the young kittens or to susceptible immature rabbits surviving from the period between the outbreaks. A virulent Lausanne strain myxoma virus was deliberately introduced by means of infective fleas (Spilopsyllus cuniculi). Field strains were present. Reactivation and transmission of virus in natural populations is discussed. The possibility of contact rather than vector (flea) transmission is examined in respect of failure to maintaining the outbreaks. Some observations were made on rabbits that recovered from myxomatosis and on the occurrence in some individuals of persistent sublethal signs of myxomatosis. Frequency of raptor predation is compared between periods with and without myxomatous rabbits. The duration of survival of infected rabbits is not significantly reduced by predation, but some raptors, such as brown hawk and little eagle, may concentrate more on the youngest available rabbits during an outbreak. ADDITIONAL ABSTRACT: High case mortalities (88-100%) were observed during two outbreaks of myxomatosis between 1973 and 1974 in a population of rabbits (Oryctolagus cuniculus), at Canberra, Australia. The presence of immune adult rabbits predisposed the disease to be confined either to the young kittens or to susceptible immature rabbits surviving from the period between the epizootics. A virulent Lausanne strain myxoma virus was deliberately introduced by means of infective Spilopsyllus cuniculi (Dale). Field strains were present. Reactivation and transmission of virus in natural populations is discussed. The possibility of contact rather than vector (flea) transmission is examined in respect of failure to maintaining the epizootics. Some observations were made on rabbits that recovered from myxomatosis and on the occurrence in some individuals of persistent sublethal signs of myxomatosis. The duration of survival of infected rabbits was not significantly reduced by predation, but some raptors sometimes concentrated more on the youngest available rabbits during an epizootic.