Susceptibility of previously untested fish species to EHN Virus, and the epidemiology of EHN Virus in the Murray Darling Basin
Whittington, R., Becker, J., Tweedie, A. and Gilligan, D., 2007. Susceptibility of previously untested fish species to EHN Virus, and the epidemiology of EHN Virus in the Murray Darling Basin. Presentation given at the Fisheries Research & Development Corporation's Aquatic Animal Health Subprogram Conference, 25–27 July 2007, Cairns, Australia.
Epizootic Haematopoietic Necrosis Virus (ENHV) is considered to be a serious threat to a number of native fish species in the Murray Darling Basin. This virus, unique to Australia, was first isolated in 1985 in redfin perch. It causes sudden mortalities and the fish display necrosis of the renal haematopoietic tissue, liver, spleen and pancreas. Experimental work by Langdon  demonstrated that a number of native species were susceptible to the disease, including the threatened Macquarie perch and silver perch, as well as mountain galaxias. The virus has been recorded from Victoria, New South Wales, South Australia and the Australian Capital Territory. The spread of EHNV has been aided by its relative resistance. It can be readily transmitted from one location to another on nets, fishing lines, boats and other equipment [2, 3]. Langdon found that the virus retained its infectivity after being stored dry for 113 days. Once EHNV has entered a water body it is considered impossible to eradicate.
Langdon (1989) tested 11 fish species for susceptibility to EHNV . For example, when Macquarie perch were held in aquaria and exposed to low concentrations of EHNV in water, all ten fish in two separate trials died. The susceptibility of other species in the Basin remains unknown. There have been no subsequent trials to validate Langdon’s findings or to test additional species. It is speculated that the sudden and severe depletion of the Macquarie perch population in Lake Eildon, Victoria, may have been partly due to EHNV. However, there are populations of Macquarie perch and silver perch still remaining in catchments that have experienced outbreaks of EHNV, which suggest that the epidemiology of the virus in the wild may be different to that recorded under laboratory conditions. The distribution of redfin perch in the Basin is still expanding through human intervention. There is a real chance that redfin will be transported past existing barriers and expose further populations of threatened species risk from the virus. The aims of this project are to validate earlier findings of susceptibility of native fish to EHNV, to determine the susceptibility to infection of a range of previously untested fish species, to investigate the epidemiology of EHNV in wild populations of priority fish species, to develop a test to determine exposure of wild populations of priority fish species and to identify the extent to which EHNV is a risk to native fish in the Murray Darling Basin.
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