![]() The virus produced a cytopathic effect different from two other small, round fish viruses detected in smelt ( Osmerus mordax) and Atlantic salmon, which induced syncytia in cell cultures whereas the trout virus caused only diffuse necrosis. The initial report of this novel virus described a small icosahedral RNA virus detected in four spawning trout populations in northern California ( Yun et al., 1988). However, virus persisted in kidney and spleen tissues of trout juveniles for four weeks post-exposure. CTV is avirulent in all fish species experimentally tested via waterborne exposure including: rainbow trout ( Oncorhynchus mykiss), brown trout ( Salmo trutta), brook trout ( Salvelinus fontinalis) and kokanee salmon (landlocked sockeye salmon, Oncorhynchus nerka). CTV is a small positive-sense, single-stranded RNA virus, that was determined to be closest to members within the family Hepeviridae (ie, human Hepatitis E virus (HEV)) based upon genome length, organization and sequence similarity. To date, CTV-like viruses have been isolated from seven different species of trout in North America, as well as from Atlantic salmon ( Salmo salar) in New Brunswick, Canada ( Table 24.1 Kibenge et al., 2000, Batts et al., 2011). ![]() Juvenile rainbow trout exposed to cutthroat trout virus were protected against subsequent experimental challenge infection with infectious hematopoietic necrosis virus (a rhabdovirus), likely as a consequence of transient interferon-mediated resistance.Ĭutthroat trout virus (CTV) was first identified in adult cutthroat trout ( Oncorhynchus clarkii) in 1988 however, later surveys found CTV in populations of trout ranging throughout the western United States ( Hedrick et al., 1991 Batts et al., 2011). However, the lack of control measures and the potential for vertical transmission may have facilitated the spread of the virus through the shipment of contaminated eggs. Control measures are not widely applied for prevention of cutthroat trout virus infection because it has not been associated with significant disease. A PCR assay can be used to identify the virus. The virus replicates in fish cells in vitro, although cytopathic effects develop slowly. The virus is most readily detected in the fluid surrounding collected eggs (ovarian fluid), or in tissues such as kidney and spleen of adult salmonid broodstocks, and there is epidemiologic evidence that the virus may be vertically transmitted to progeny via the egg. Rainbow trout, brown trout, and kokanee salmon ( Oncorhynchus nerka) are all susceptible to experimental infection with cutthroat trout virus whereas Chinook ( Oncorhynchus tshawytscha) and coho ( Oncorhynchus kisutch) salmon are apparently refractory. ![]() However, the cutthroat trout virus has yet to be associated with hepatitis or any other clinical syndrome. The virus is currently recognized in only North America, but has increasingly been identified in adult salmonid broodstock, including rainbow trout ( Oncorhynchus mykiss), cutthroat trout ( Oncorhynchus clarkii), brown trout ( Salmo trutta), and brook trout ( Salvelinus fontinalis) in several western states of the United States. Although this virus is of similar size and morphology as other hepeviruses, it shares only approximately 13–27% amino acid sequence identity with members of the genus Orthohepevirus. In Fenner's Veterinary Virology (Fifth Edition), 2017 CUTTHROAT TROUT VIRUS (PISCIHEPEVIRUS A)Ĭutthroat trout virus, recently designated as Piscihepevirus A, was first identified in salmonid fish in California in 1988.
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