Genomic and immunogenic changes over the history of the Viral Hemorrhagic Septicemia (VHS-IVb) fish virus (=Piscine novirhabdovirus) in the Laurentian Great Lakes

Abstract

26 27 Viral Hemorrhagic Septicemia Virus (VHSV) (=Piscine novirhabdovirus) appeared in the 28 Laurentian Great Lakes in 2005, constituting a unique and highly virulent genogroup (IVb), 29 which killed >32 fish species in large 2005 and 2006. Periods of apparent dormancy punctuated 30 smaller outbreaks in 2007, 2008, and 2017. We conducted the first whole genome analysis of 31 IVb, evaluating its evolutionary changes using 46 isolates, in reference to immunogenicity in cell 32 culture, and the genomes of other VHS genogroups (I-IVa) and other Novirhabdoviruses. IVb 33 isolates had 253 genomic nucleotide substitutions (2.3% of the total 11,158 nucleotides), with 85 34 (16.6%) being non-synonymous. The greatest number of substitutions occurred in the non-35 coding region (NCDS; 4.3%) followed by the Nv-(3.8%), and M-(2.8%) genes. The M-gene 36 possessed the greatest proportions of amino acid changes (52.9%), followed by the Nv-(50.0%), 37G-(48.6%), N-(35.7%) and L-(23.1%) genes. Among VHS genogroups, IVa from the 38 northeastern Pacific exhibited the fastest substitution rate (2.01x10-3), followed by IVb 39 (6.64x10 -5), and I/III from Europe (4.09x10 -5). A 2016 gizzard shad isolate from Lake Erie was 40 the most divergent IVb isolate (38 NT, 15.0%, 15 AA), yet exhibited reduced virulence with in 41 vitro immunogenicity analyses, as did other 2016 isolates, in comparison to the first IVb isolate 42 (2003). The 2016 isolates exhibited lower impact on innate antiviral responses, suggesting 43 phenotypic effects. Results suggest continued sequence change and lower virulence over the 44 history of IVb, which may facilitate its long-term persistence in fish host populations. 45 46