Geographic and host factors shape the evolution of a newly recognized subgroup within the U genogroup of the fish rhabdovirus IHNV

Abstract

Infectious hematopoietic necrosis virus (IHNV) is an aquatic rhabdovirus of Pacific salmonids that causes frequent epidemics. We analyzed data on U genogroup IHNV detections from 1971 to 2013 in Washington, Oregon, and Idaho. Using Bayesian coalescent analysis we discovered two previously unrecognized subgroups: UC and UP. Descriptive epidemiological analysis showed that both subgroups displayed host and geographic specificity. UC viruses were detected predominantly in Chinook salmon and steelhead trout in the Columbia River Basin and UP viruses were detected predominantly in sockeye salmon in Washington coastal watersheds. Statistical analysis indicated that viral populations were structured by host species of detection and by geographic range. Our findings indicate that the UC subgroup likely resulted from an adaptation of U genogroup IHNV to Chinook salmon in the Columbia River Basin due to a human-caused shift in host abundance. This work demonstrates anthropogenic influence as a selection driver of viral genetic diversity.