THE INTERACTION OF CHINOOK SALMON (ONCORHYNCHUS TSHAWYTSCHA) WITH THE U, M, AND L GENOGROUPS OF INFECTIOUS HEMATOPOIETIC NECROSIS VIRUS
Daniel Hernandez1, Gael Kurath2, Thomas Quinn1.
1School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, 2United States Geological Survey, Western Fisheries Research Center, Seattle, WA.
Infectious hematopoietic necrosis virus (IHNV) is an acute viral pathogen that causes significant disease and mortality in wild and cultured salmonids. Genetic sequencing of hundreds of virus isolates has identified 3 genetic subgroups of IHNV designated U (upper), M (middle), and L (lower) for their relative geographic occurrence in western North America. Each genogroup of IHNV contains many individual isolates, and genogroup-specific patterns of host specificity have been observed. In the Columbia River Basin (CRB), IHNV has been detected regularly in Chinook salmon since 1973 but primarily in the form of asymptomatic infection of adult fish with the U and M group viruses. A lack of disease in juvenile Chinook salmon in the CRB led to the belief that Chinook were refractory to disease caused by both the U and M genetic subgroups of IHNV, thus their potential role in the epidemiology of the virus throughout the CRB had gone unexplored. Our current investigation aims to describe the infection kinetics of the most commonly detected isolates of U and M IHNV in 4 populations of juvenile Chinook representative of the genetic and life history diversity present in the CRB. Using a viral plaque assay and an IHNV glycoprotein gene reverse transcriptionâ€“quantitative polymerase chain reaction (RT-qPCR) assay, we have confirmed infection and quantified viral load from the tissues of fish experimentally challenged with U and M IHNV. Our approach and methodology have made it possible to begin discerning the role of Chinook salmon in the ecology of IHNV in the CRB.