READ THIS Latest Development - Escaped Virus !
Rabbit Calcivirus Disease (RCD), also known as viral haemorrhagic disease (VHD) and rabbit haemorrhagic disease (RHD), is caused by a calicvirus which has potential as a biological control agent. It appears to be a new disease of rabbits which possibly crossed from another mammal host species. It was first observed in China in 1984 and in Europe in 1988. In Italy it is estimated to have killed 30 million domestic rabbits. In Czechoslovakia, retrospective examination of earlier blood samples of rabbits showed that antibodies to the virus were present in blood samples collected 12 years before the virulent strain was detected. The disease in now endemic in populations of wild rabbits in Europe. Studies to date indicate that the disease is species specific, infecting the European wild rabbit and the domestic strains derived from the wild rabbit. There are no external signs of the disease until 24 hours after infection, when the rabbits become listless with a high temperature. Rabbits at the CSIRO high security laboratory in Geelong died quietly 30-40 hours after infection with no indication of distress. At autopsy the spleen and liver are swollen. Due to extensive death of cells, the liver is pale and crumbly. The effects on the lungs are variable but they may fill up with fluids and the blood vessels blocked by fibrin. The cause of death is probably and acute lack of oxygen and heart failure.
Nestling rabbits, less that 18 days old, do not die, but excrete the virus and develop antibodies. The mortality rate of at Geelong to the virulent strain was 50% for 4-5 weeks old rabbits and more than 95% for rabbits nine weeks or older. It is not known whether rabbits would be susceptible to a second infection. The disease is highly infectious by contact and there are indications that it may also be spread by insects. Despite the short period of infectivity, RCD spread rapidly through the wild populations in Spain, 15 km per month, with infection rates and mortality rates of about 90%. It is not known how the disease persists in the field. Carrier rabbits are a possibility, although there is no evidence for this. The virus can be detected in frozen rabbit meat and may persist in protected environments, such as warrens for six months.
Promising results from preliminary testing at the Australian Animal Health Laboratory mean that it is now appropriate to assess the possibility of releasing the virus into the filed. Should the release occur, it would require the approval of the Commonwealth Minister for Primary Industries and Energy, whose Department administers the Quarantine Act. Other Ministers, notably the Minister for the Environment, may well be involved in the ultimate decision. Their decision on the release of RHD will rest on an assessment of the scientific evidence relating to (1) host specificity; (2) economic and conservation impacts; (3) animal welfare considerations; (4) effectiveness; (5) community views on the potential release of a relatively new and unknown virus. It will be a significant decision.
The information on this page was imported from the publication "Managing Vertebrate Pests" CSIRO Divsion of Wildlife and Ecology. See References
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