A winter epizootic of myxomatosis in subalpine south-eastern Australia

Abstract

An epizootic of myxomatosis in rabbits that occurred during the winter months (March-August) of 1969 is described in detail. Virus of virulence grade 111, the common virulence of field strains of myxoma virus presently in Australia, was isolated during the epizootic. The estimated case mortality was 86% over the 5 months during which the epizootic was active. Only 41228 of the original susceptible and established population completely avoided infection. Transmission through the population was relatively slow and apparently depended on social contact between individual rabbits. The seasonal conditions and the slow progression of the disease through the population make it most unlikely that mosquitoes were involved in transmitting the virus. The origin of the virus that initiated the epizootic is discussed, including the possibility that it was not a reintroduction of myxoma virus to the population. This implies that the virus may have remained latent in the rabbit population for several years.

Myxomatosis in farmland rabbit populations in England and Wales

“…A more reliable method was required to assess the situation during the 1970s in Britain, where a much lower kill rate was expected than for the original outbreaks. The method adopted in detailed studies of myxomatosis in Australia (18,19) was considered appropriate, combining estimates of the proportion of rabbits infected during individual 335 outbreaks and the proportion of these infected rabbits that died from the disease. The characteristics of myxomatosis outbreaks and the effects of the disease were investigated as part of a wider study of the population dynamics of rabbits on three farmland sites between 1971 and 1978 in the UK.…”

Fluctuations in the titre of antibody to a soluble antigen of myxoma virus in field populations of rabbits,Oryctolagus cuniculus(L.), in Australia

“…However, where field strains operate at low temperatures (i.e. in winter), amongst rabbits in which the genetic resistance is low, and maternal antibodies are absent, the chances of recovery are low (Dunsmore et al 1971;Williams, Fullagar et al 1972, Williams et al 1973.…”

“…Additionally, in such summer and winter epizootics which have been studied in detail Dunsmore et al 1971;Williams, Fullagar et al 1972, 1973) the re-activation of latent virus resulting in overt infection in certain rabbits was considered to be the source of virus initiating the epizootics. In these cases, climatic conditions and population density were such that they could be regarded as stressful in the periods immediately before the epizootics.…”

“…In contrast to the situation at Urana, myxomatosis at Snowy Plains does not appear to occur annually. Details of the myxomatosis history at Snowy Plains from 1967 until 1972 have been set out elsewhere (Dunsmore, Williams & Price, 1971;Dunsmore & Price, 1972). Briefly, an outbreak of the disease was in progress when the study began in March 1967, and all the animals entering the 1967 breeding season, which at Snowy Plains lasts only from October to December each year, were survivors of the outbreak.…”

Myxomatosis: passive immunity in the offspring of immune rabbits (Oryctolagus cuniculus) infested with fleas (Spilopsyllus cuniculiDale) and exposed to myxoma virus

“…Despite the long periods during which maternal antibody titres remain high in serum it was decided to examine the epidemiological consequences of passive immunity under Australian conditions. This seemed necessary because of reports of winter epizootics by Dunsmore, Williams & Price (1971) and Williams, Fullager, Davey & Kogon (1972) and also because of the introduction of the European rabbit flea into Australia (Sobey & Conolly, 1971) with the consequent possibility of virus being spread throughout the year including the breeding season. The main question is whether passive immunity up to 8 weeks is of any consequence to the population.…”