Iridovirus infections in finfish - critical review with emphasis on ranaviruses

Viruses in three genera of the family Iridoviridae (iridoviruses) affect finfish. Ranaviruses and megalocytiviruses are recently emerged pathogens. Both cause severe systemic disease, occur globally and affect a diversity of hosts. In contrast, lymphocystiviruses cause superficial lesions and rarely...

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Bibliographic Details
Published in:Journal of fish diseases 2010-02, Vol.33 (2), p.95-122
Main Authors: Whittington, R.J, Becker, J.A, Dennis, M.M
Format: Article
Language:English
Subjects:
amphibian
amphibians
Amphibians - virology
Animals
Antibodies, Viral
Disease Reservoirs - veterinary
Disease Susceptibility
DNA Virus Infections - epidemiology
DNA Virus Infections - prevention & control
DNA Virus Infections - transmission
DNA Virus Infections - veterinary
epidemiology
fish
Fish Diseases - epidemiology
Fish Diseases - prevention & control
Fish Diseases - transmission
Fish Diseases - virology
Fishes - virology
Iridoviridae
Iridovirus
Marine
Megalocytivirus
Prevalence
Ranavirus
Ranavirus - classification
Ranavirus - genetics
Ranavirus - pathogenicity
Ranavirus - physiology
Reptiles - virology
Singapore Grouper Iridovirus
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Summary:Viruses in three genera of the family Iridoviridae (iridoviruses) affect finfish. Ranaviruses and megalocytiviruses are recently emerged pathogens. Both cause severe systemic disease, occur globally and affect a diversity of hosts. In contrast, lymphocystiviruses cause superficial lesions and rarely cause economic loss. The ranavirus epizootic haematopoietic necrosis virus (EHNV) from Australia was the first iridovirus to cause epizootic mortality in finfish. Like other ranaviruses, it lacks host specificity. A distinct but closely related virus, European catfish virus, occurs in finfish in Europe, while very similar ranaviruses occur in amphibians in Europe, Asia, Australia, North America and South America. These viruses can be distinguished from one another by conserved differences in the sequence of the major capsid protein gene, which informs policies of the World Organisation for Animal Health to minimize transboundary spread of these agents. However, limited epidemiological information and variations in disease expression create difficulties for design of sampling strategies for surveillance. There is still uncertainty surrounding the taxonomy of some putative ranaviruses such as Singapore grouper iridovirus and Santee-Cooper ranavirus, both of which cause serious disease in fish, and confusion continues with diseases caused by megalocytiviruses. In this review, aspects of the agents and diseases caused by ranaviruses are contrasted with those due to megalocytiviruses to promote accurate diagnosis and characterization of the agents responsible. Ranavirus epizootics in amphibians are also discussed because of possible links with finfish and common anthropogenic mechanisms of spread. The source of the global epizootic of disease caused by systemic iridoviruses in finfish and amphibians is uncertain, but three possibilities are discussed: trade in food fish, trade in ornamental fish, reptiles and amphibians and emergence from unknown reservoir hosts associated with environmental change.
ISSN:0140-7775
1365-2761
DOI:10.1111/j.1365-2761.2009.01110.x