Epizootic haematopoietic necrosis virus: epidemiology and uncertainty
2009
Nguyen, T. | Dixon, R. | Hyatt, A. | Whittington, R. | Li, L.
Epizootic haematopoietic necrosis virus (EHNV) was the first virus isolated from fish in Australia, and the first iridovirus associated with systemic infection and epizootic mortality. It is one of only five diseases of finfish that are notifiable to the Office International des Epizooties (OIE). The EHNV causes epizootic mortality in wild redfin perch (Perca fluviatilis) and a fatal disease of low prevalence in farmed rainbow trout (Oncorhynchus mykiss), while related viruses (European sheatfish virus, SV/European catfish virus, ECV) cause epizootic mortality in sheatfish (Silurus glanis) and catfish (Ictalurus melas) in Europe. Being an indiscriminate pathogen, EHNV lacks host specificity but displays considerable variation in virulence in different species of finfish. Detection of EHNV in rainbow trout can be difficult because the mortality rate may barely rise above background levels. However, EHNV can be detected in affected fish among ‘routine’ mortalities and may be associated with specific antibodies in a small proportion of older fish. Sampling to detect EHNV for certification purposes should be based on examination of ‘routine’ mortalities rather than random samples of live fish. Further studies are needed to identify the environmental reservoir of the ranaviruses found in finfish because fish may be accidental hosts. The natural reservoir could be among the amphibians and reptiles because redfin perch, sheath fish and catfish seem to be too susceptible and rainbow trout, too resistant to account for the ecological persistence of the virus. This research will assist in the critical assessment of the role of legal and illegal trade in food fish, ornamental fish, reptiles and amphibians in the trans-border spread of these viruses.
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