The status of myxomatosis at Urana, New South Wales, from 1968 until 1971

Abstract

Epizootics of myxomatosis which occurred each year from 1968 until 1971 in a rabbit population inhabiting a 700-acre study site at Urana, N.S.W., were studied. Transmission was rapid in 1968 and 1969, Anopheles annulipes being the vector, and the peak of these epizootics occurred in early November. Transmission in 1970 was primarily by the flea Spilopsyllus cuniculi, and was slower, but the midpoint of the epizootic still occurred in early November. In 1971 the epizootic peaked in late December, transmission was rapid, and the vector was unknown. Each year, about 75% of the susceptible animals older than 3 months of age at the time of the epizootic contracted myxomatosis; of these, 60% recovered, and of the recoveries, 20% died between the time of recovery (early December) and 1 January. Fewer animals (16-55 %) under 3 months of age were seen with myxomatosis; of these, about 50% were seen to recover, and a large proportion (from 25 to 45%) of animals seen to recover died before 1 January each year. The great majority of animals not seen to contract myxomatosis probably died from other causes without being exposed to the disease. These data indicate that myxomatosis killed very few animals directly during these epizootics, and that other factors were responsible for the majority of deaths which occurred during the epizootic period. In 1968, 1969, and 1970, reactivation of latent virus in animals which had previously recovered from myxomatosis was probably the source of the virus which initiated the epizootics.