In vivo and in vitro phenotypic differences between Great Lakes VHSV genotype IVb isolates with sequence types vcG001 and vcG002

Abstract

Viral hemorrhagic septicemia virus (VHSV) is an aquatic rhabdovirus first recognized in farmed rainbow trout in Denmark. In the past decade, a new genotype of this virus, IVb was discovered in the Laurentian Great Lakes basin and has caused several massive die-offs in some of the 28 species of susceptible North American freshwater fishes. Since its colonization of the Great Lakes, several closely related sequence types within genotype IVb have been reported, the two most common of which are vcG001 and vcG002. These sequence types have different spatial distributions in the Great Lakes. The aim of this study was to determine whether the genotypic differences between representative vcG001 (isolate MI03) and vcG002 (isolate 2010-030 #91) isolates correspond to phenotypic differences in terms of virulence using both an in vitro and in vivo approach. In vitro infection of epithelioma papulosum cyprini (EPC), bluegill fry (BF-2), and Chinook salmon embryo (CHSE) cells demonstrated some differences in onset and rate of growth in EPC and BF-2 cells, without any difference in the quantity of RNA produced. In vivo infection of round gobies (Neogobius melanostomus) via immersion exposure to different concentrations of vcG001 or vcG002 caused a significantly greater mortality in round gobies exposed to 102 plaque forming units ml−1 of vcG001. These experiments suggest that there are phenotypic differences between Great Lakes isolates of VHSV genotype IVb.

Gene Diversification of an Emerging Pathogen: A Decade of Mutation in a Novel Fish Viral Hemorrhagic Septicemia (VHS) Substrain since Its First Appearance in the Laurentian Great Lakes

“…The objective of our investigation is to analyze the relative evolutionary and biogeographic differentiation patterns of VHSv-IVb among different genes over temporal and spatial distribution in the Great Lakes, building on some prior knowledge of its glycoprotein ( G -) gene variability [ 2 , 6 ]. Studies have indicated that some VHSv-IVb G -gene variants differ in their relative virulence [ 8 ]. Swift differentiation of genetic variants may allow the virus to evade host immune responses, persist in populations, and spread to new areas and hosts [ 2 , 9 ].…”

Genomic and immunogenic changes of Piscine novirhabdovirus (Viral Hemorrhagic Septicemia Virus) over its evolutionary history in the Laurentian Great Lakes

“…Other studies observed similar trends. For example, Imanse et al [ 43 ] examined vcG001 (C03MU) and vcG002 (not included in our analysis), finding faster growth but lower titers in cells exposed to vcG002. These had similar levels of viral RNA, suggesting that vcG002 was less efficient at producing infective particles.…”

“…1 μl of each cDNA was tested using RT-qPCR, with 5 μl of the Radiant Green Lo-ROX 2X qPCR kit (Alkali Scientific), 50 ng of each oligonucleotide, and water to total 10 μl. Primers used were: VHSV-Nse/as, EPC IFN se/as, and β-actin se/as [ 43 ]. Reactions and data collections were performed on a C1000 Real Time Thermocycler (Bio-Rad), with initial 3 min denaturation at 95°C, followed by 40 cycles of 15 s at 95°C, and 30 s elongation at 60°C.…”

“…Just two other investigations (that we know of),have compared adaptive traits of the original VHSV-IVb 2003 isolate to those of other naturally occurring VHSV-IVb isolates. Notably, Imanse et al [ 43 ] found that an isolate from a 2010 round goby ( Neogobius melanostomus ) in the St. Lawrence River, NY; GenBank: EF564588.1) showed reduced virulence and lower mortality in comparison to the original 2003 M103GL isolate (GenBank: GQ385941). A study by Getchell et al [ 44 ] discerned lower viral titers, which did not lead to mortality, for a round goby isolate from 2006 and two gizzard shad isolates (from 2013 and 2014) in a laboratory challenge experiment that infected northern pike fry via immersion, versus greater virulence and mortality with the original 2003 VHSV-IVb isolate (M103GL = CO3MU).…”

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

“…Other studies observed similar trends. For example, Imanse et al [44] 606 examined vcG001 (C03MU) and vcG002 (not included in our analysis), finding faster growth 607 but lower titers in cells exposed to vcG002. Those had similar levels of viral RNA, suggesting 608 that vcG002 was less efficient at producing infective particles.…”