Alphavirus infections in salmonids – a review

Abstract

The first alphavirus to be isolated from fish was recorded in 1995 with the isolation of salmon pancreas disease virus from Atlantic salmon, Salmo salar L., in Ireland. Subsequently, the closely related sleeping disease virus was isolated from rainbow trout, Oncorhynchus mykiss (Walbaum), in France. More recently Norwegian salmonid alphavirus (SAV) has been isolated from marine phase production of Atlantic salmon and rainbow trout in Norway. These three viruses are closely related and are now considered to represent three subtypes of SAV, a new member of the genus Alphavirus within the family Togaviridae. SAVs are recognized as serious pathogens of farmed Atlantic salmon and rainbow trout in Europe. This paper aims to draw together both historical and current knowledge of the diseases caused by SAVs, the viruses, their diagnosis and control, and to discuss the differential diagnosis of similar pathologies seen in cardiomyopathy syndrome and heart and skeletal muscle inflammation of Atlantic salmon.

Comparative Pathology of Ranaviruses and Diagnostic Techniques

“…Virus neutralization tests cannot be used because antibodies with neutralizing activity to EHNV were not evoked following immunization of rabbits (Hedrick et al 1992 ) or from mouse monoclonal antibodies (Monini and Ruggeri 2002 ). Current knowledge of the amphibian, reptile, and piscine immune systems indicates limitations to serological techniques that are imposed by a lack of affi nity maturation, poor immune memory, and temperature dependence of the response (McLoughlin and Graham 2007 ). For this reason, the OIE does not currently support serology as a useful strategy.…”

Identification of an additional two-cysteine containing type I interferon in rainbow trout Oncorhynchus mykiss provides evidence of a major gene duplication event within this gene family in teleosts

“…Salmon alpha virus (SAV), containing a single-stranded positive RNA genome, is known to cause sleeping disease in salmonids (McLoughlin and Graham 2007). Alpha viruses enter the cytoplasm of host cells using receptormediated endocytosis by pH-dependent fusion with the endosomal wall and replicate in cytopathic vacuoles, exposing viral RNA to endosomal pattern recognition receptors (PRRs), which are known to activate the interferon system.…”

Natural infection of Atlantic salmon (Salmo salar L.) with salmonid alphavirus 3 generates numerous viral deletion mutants

“…Pancreas disease (PD) is an economically important disease in European salmonid aquaculture affecting both Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss) (McLoughlin & Graham, 2007). The disease is characterized by degeneration and necrosis of cardiomyocytes with subsequent inflammation, pancreatic acinar cell loss and subsequent skeletal muscle degeneration (McLoughlin et al, 2006;McVicar, 1987).…”