Hepatitis E Virus in Cutthroat Trouts

In 1988 a novel virus was isolated from spawning adult trout in the state of California (USA). Provisionally termed the cutthroat trout (Oncorhynchus clarkii) virus (CTV), the small, round virus was not associated with disease in fish[1].

Alarmingly, it was subsequently found to be present in an increasing number of trout populations in the western USA, likely by a combination of improved surveillance activities and the shipment of infected eggs to new locations.

Further analysis revealed that the genome of cutthroat trout (Oncorhynchus clarkii) virus was similar in size and organization to that of Hepatitis E Virus (HEV) with which it shared the highest nucleotide and amino acid sequence identities. The data indicated that cutthroat trout (Oncorhynchus clarkii) virus was clearly a member of the family Hepeviridae, although the level of amino acid sequence identity with the ORFs of mammalian or avian hepeviruses (13-27%) may be sufficiently low to warrant the creation of a novel genus.

Analysis of isolates, obtained from seven species of trout, reared in various geographic locations in the western USA, revealed that there was little diversion between the virus, suggesting an epidemiological link.

The Hepatitis E Virus from fish has been used as a surrogate infection model[2]. It would be really remarkable if the recently discovered White Sucker Hepatitis B Virus (WSHBV) offered the same opportunities.

[Suggested classification of the family Hepaviridae]

The virus surely needs to be renamed to Cuttroat Trout Hepatitis E Virus, shortened to CTHEV. However, the scientific world has suggested to put this virus into a genus of its own, the Piscihepavirus and Cuttroat Trout Hepatitis E Virus will probably be named Piscihepevirus A[3].

[1] Batts et al: A novel member of the family Hepeviridae from cutthroat trout (Oncorhynchus clarkii) in Journal of Virology – 2011
[2] Debing et al: Cutthroat trout virus as a surrogate in vitro infection model for testing inhibitors of hepatitis E virus replication in Antiviral Research – 2013
[3] Smith et al: Consensus proposals for classification of the family Hepeviridae in Journal of General Virology - 2014