DAO 104:179-195 (2013)  -  DOI: https://doi.org/10.3354/dao02596

Emergence of MD type infectious hematopoietic necrosis virus in Washington State coastal steelhead trout

Rachel Breyta1,2,*, Amelia Jones1,2, Bruce Stewart3, Ray Brunson4, Joan Thomas5, John Kerwin5, Jim Bertolini3, Sonia Mumford4, Chris Patterson4, Gael Kurath2

1University of Washington, Seattle, Washington 98195, USA
2US Geological Survey Western Fisheries Research Center, Seattle, Washington 98115, USA
3Northwest Indian Fisheries Commission, Olympia, Washington 98516, USA
4US Fish and Wildlife Service Lacey, Washington 98503, USA
5Washington Department of Fish and Wildlife, Olympia, Washington 98501, USA

ABSTRACT: Infectious hematopoietic necrosis virus (IHNV) occurs in North America as 3 major phylogenetic groups designated U, M, and L. In coastal Washington State, IHNV has historically consisted of U genogroup viruses found predominantly in sockeye salmon Oncorhynchus nerka. M genogroup IHNV, which has host-specific virulence for rainbow and steelhead trout O. mykiss, was detected only once in coastal Washington prior to 2007, in an epidemic among juvenile steelhead trout in 1997. Beginning in 2007 and continuing through 2011, there were 8 IHNV epidemics in juvenile steelhead trout, involving 7 different fish culture facilities in 4 separate watersheds. During the same time period, IHNV was also detected in asymptomatic adult steelhead trout from 6 coastal watersheds. Genetic typing of 283 recent virus isolates from coastal Washington revealed that the great majority were in the M genogroup of IHNV and that there were 2 distinct waves of viral emergence between the years 2007 and 2011. IHNV type mG110M was dominant in coastal steelhead trout during 2007 to 2009, and type mG139M was dominant between 2010 and 2011. Phylogenetic analysis of viral isolates indicated that all coastal M genogroup viruses detected in 1997 and 2007 to 2011 were part of the MD subgroup and that several novel genetic variants related to the dominant types arose in the coastal sites. Comparison of spatial and temporal incidence of coastal MD viruses with that of the rest of the Pacific Northwest indicated that the likely source of the emergent viruses was Columbia River Basin steelhead trout.

KEY WORDS: IHNV · Phylogenetic · Rhabdovirus · Oncorhynchus mykiss · Oncorhynchus nerka · Washington · North America

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Cite this article as: Breyta R, Jones A, Stewart B, Brunson R and others (2013) Emergence of MD type infectious hematopoietic necrosis virus in Washington State coastal steelhead trout. Dis Aquat Org 104:179-195. https://doi.org/10.3354/dao02596

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