Viral Hemorrhagic Septicemia virus (VHSv) causes one of the world?s most important finfish diseases. An outbreak of a unique and emerging strain (IVb) has been observed across the Great Lakes since 2005, killing many important species and harming our fisheries, baitfish, aquaculture, and tourism industries. This study will analyze the evolutionary, biogeographic, and genetic diversity patterns of this ?new? VHS strain throughout its distribution, in comparison to other strains, providing important benefits for understanding and combating this disease. DNA sequence variation and biogeographic patterns will be tested across the virus?s geographic range, temporal course, and among infected fish species. Genetic diversity within and among the strains will be analyzed using three different genes, permitting the tracking of the patterns of viral variation over time and space.
This investigation will significantly enhance the research depth and opportunity of a female Ph.D. student. Additional broader impacts are that the project will promote teaching, training, collaboration, and understanding of evolutionary patterns in pathogens to fellow graduate students, high school students, university and state researchers, aquaculture fish farmers, and fisheries managers. Results will enhance fisheries conservation and disease prevention efforts.
This NSF DDIG project greatly enhanced the dissertation of a young female scientist and provided collaboration and mentoring opportunities at tiered educational levels. Outputs from this work included 20+ scientific presentations, two publications (one in 2012 published in Molecular Phylogenetics and Evolution, and another in review), a VHSv webpage on our University of Toledoâ€™s Lake Erie Center website detailing the biology, background, and current findings of the project (www.utoledo.edu/nsm/lec/research/glgl/VHS/VHS_ main.html), and a lesson plan/game for high school students on VHSv characteristics and its phylogenetic classification (available for download at – www.utoledo.edu/nsm /lec/gk12_grant/Lesson_Plans.html). In addition, several partnerships were gained during this work to obtain samples for genetic analysis, with: USGS Western Fisheries Research Center (Seattle, WA), Canada Fisheries and Oceans (Ottawa, Canada), the Finnish Food Safety Authority Evira (Helsinki, Finland), and the Michigan Department of Natural Resources (East Lansing, Michigan). We analyzed the phylogenetic, biogeographic, and genetic patterns of all VHSv strains and investigated the diversification and spread of the new and highly virulent strain IVb throughout its Great Lakes distribution using several gene regions. Specifically, for work published in Molecular Phylogenetics and Evolution, we found that: (1) phylogenies based on the glycoprotein (G), nucleoprotein (N), and non-virion (Nv) genes are congruent, (2) there is little saturation of phylogenetic signal in all three genes, (3) all four VHSv strains group separately on the phylogenetic tree indicating monophyly and vicariant evolution, (4) substrain IVc comprises a separate taxon, (5) genetic diversity levels of VHSv are relatively high, with strains I and IV having the most haplotypes, (6) strain IV appears the most divergent from the other three strains, with strains I-III being more closely related to each other, (7) strains I and IV occur in a wide variety of habitat regimes (marine, estuarine, and freshwater), and are more geographically widespread, whereas II and III are exclusively marine/estuarine and appear less diverse, (8) the evolutionary trajectory of the three genes did not conform to a molecular clock hypothesis, (9) the Nv-gene evolves the fastest, followed by the N and G, and (10) VHSv-IVb follows a quasispeices model of evolution. Findings for work in review include: (1) 19 unique IVb sequences in the Great Lakes were identified, (2) two new unique gene variants were discerned for the G and Nv genes that were collected by us in Lake Erie in 2012, (3) the Nv-gene for IVb evolves the quickest, followed by the G, P, and M genes, (4) patterns of haplotype changes coincide among the four genes for some of the isolates, but appear independent in others, and (5) collective genetic diversity appears greatest in Lakes Erie and Ontario. We are continuing to collaborate and investigate the evolution and diversification of VHSv by collecting additional IVb samples for sequencing. Dr. Stepien obtained a new NSF grant with Dr. Leaman to continue these investigations. Our continued efforts will enhance fisheries conservation and disease prevention efforts by providing the most up to date information on how and why the virus is changing over time and space.