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Susceptibility of previously untested fish species to EHN Virus, and the epidemiology of EHN Virus in the Murray Darling Basin

Authors:
Susceptibility of previously untested fish species to EHN Virus, and the
epidemiology of EHN Virus in the Murray Darling Basin
Richard Whittington1, Joy Becker1, Alison Tweedie1 and Dean Gilligan2
1Faculty of Veterinary Science, The University of Sydney, Camden
2NSW Department of Primary Industries, Fisheries Research Centre, Narranderra
Funding source: Murray Darling Basin Commission
Introduction
Epizootic Haematopoietic Necrosis Virus(EHNV) 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 [1] 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 ACT. The spread of EHNV has
been aided by its relative resistance. It can be readily transmitted from one location
to another in water, by infected fish, and likely also 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 tested 11 fish species for susceptibility to EHNV [1] (Table 1). 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 most 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 suggests that the epidemiology of this 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 activity. There is a real
chance that redfin will be transported past existing barriers and expose further
populations of threatened species to 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 an
immunological 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. The project commenced in 2007.
References
[1] Langdon, J. S., J. Fish Dis. 1989, 12, 295-310.
[2] Whittington, R. J., Kearns, C., Hyatt, A. D., Hengstberger, S., Rutzou, T., Aust.
Vet. J. 1996, 73, 112-114.
[3] Whittington, R. J., Reddacliff, L. A., Marsh, I., Kearns, C., et al., Dis. Aquat. Org.
1999, 35, 125-130.
Table 1. Susceptibility of finfish to EHNV. Most data are from Langdon[1]
NoNoNoAustralian smelt R semonii
NoNoNoBarramundi L calcarifer
NoNoNoGoldfish and carp
No; 30% carrierNoNoAtlantic salmon S salar
20% diedNoNoAustralian bass M novemacuelata
all diedNoNoGolden perch M ambigua
all diedNo; 20% carrierNoMurray cod M peeli
not testedall diedNoMountain galaxias G olidus
+ died+ diedNoMosquito fish G affinis
all died30-60% diedNoSilver perch B bidyanus
all diedall diedNoMacquarie perch M australasica
++/-YesRainbow trout
++++++++YesRedfin perch
InjectionImmersion
Susceptible to Natural
infection
reported
Host
NoNoNoAustralian smelt R semonii
NoNoNoBarramundi L calcarifer
NoNoNoGoldfish and carp
No; 30% carrierNoNoAtlantic salmon S salar
20% diedNoNoAustralian bass M novemacuelata
all diedNoNoGolden perch M ambigua
all diedNo; 20% carrierNoMurray cod M peeli
not testedall diedNoMountain galaxias G olidus
+ died+ diedNoMosquito fish G affinis
all died30-60% diedNoSilver perch B bidyanus
all diedall diedNoMacquarie perch M australasica
++/-YesRainbow trout
++++++++YesRedfin perch
InjectionImmersion
Susceptible to Natural
infection
reported
Host
... Although redfin perch is the only species to succumb to EHNV in the wild, the virus has caused mortalities of rainbow trout in fish farms (Whittington et al. 1999). Despite there being no reported cases of EHNV causing mortality of native fish species, laboratory tests have shown several species are susceptible to the virus, while others may act as natural hosts and / or subclinical carriers (Becker et al. 2013, Whittington et al. 2015. The susceptibility of brown trout and Chinook salmon to EHNV is unknown. ...
  • R J Whittington
  • L A Reddacliff
  • I Marsh
  • C Kearns
Whittington, R. J., Reddacliff, L. A., Marsh, I., Kearns, C., et al., Dis. Aquat. Org. 1999, 35, 125-130.