Stepien Carol A, Pierce Lindsey R, Leaman Douglas W, Niner Megan D, Shepherd Brian S
Great Lakes Genetics/Genomics Laboratory, Lake Erie Center and Department of Environmental Sciences, The University of Toledo, Toledo, Ohio, 43616, United States of America.
Department of Biological Sciences, The University of Toledo, Toledo, Ohio, 43606, United States of America.
PLoS One. 2015 Aug 27;10(8):e0135146. doi: 10.1371/journal.pone.0135146. eCollection 2015.
Viral Hemorrhagic Septicemia virus (VHSv) is an RNA rhabdovirus, which causes one of the world's most serious fish diseases, infecting >80 freshwater and marine species across the Northern Hemisphere. A new, novel, and especially virulent substrain-VHSv-IVb-first appeared in the Laurentian Great Lakes about a decade ago, resulting in massive fish kills. It rapidly spread and has genetically diversified. This study analyzes temporal and spatial mutational patterns of VHSv-IVb across the Great Lakes for the novel non-virion (Nv) gene that is unique to this group of novirhabdoviruses, in relation to its glycoprotein (G), phosphoprotein (P), and matrix (M) genes. Results show that the Nv-gene has been evolving the fastest (k = 2.0 x 10-3 substitutions/site/year), with the G-gene at ~1/7 that rate (k = 2.8 x 10-4). Most (all but one) of the 12 unique Nv- haplotypes identified encode different amino acids, totaling 26 changes. Among the 12 corresponding G-gene haplotypes, seven vary in amino acids with eight total changes. The P- and M- genes are more evolutionarily conserved, evolving at just ~1/15 (k = 1.2 x 10-4) of the Nv-gene's rate. The 12 isolates contained four P-gene haplotypes with two amino acid changes, and six M-gene haplotypes with three amino acid differences. Patterns of evolutionary changes coincided among the genes for some of the isolates, but appeared independent in others. New viral variants were discovered following the large 2006 outbreak; such differentiation may have been in response to fish populations developing resistance, meriting further investigation. Two 2012 variants were isolated by us from central Lake Erie fish that lacked classic VHSv symptoms, having genetically distinctive Nv-, G-, and M-gene sequences (with one of them also differing in its P-gene); they differ from each other by a G-gene amino acid change and also differ from all other isolates by a shared Nv-gene amino acid change. Such rapid evolutionary differentiation may allow new viral variants to evade fish host recognition and immune responses, facilitating long-time persistence along with expansion to new geographic areas.
病毒性出血性败血症病毒（VHSv）是一种RNA弹状病毒，它会引发世界上最严重的鱼类疾病之一，感染北半球80多种淡水和海洋物种。大约十年前，一种新的、特别具有毒性的亚毒株——VHSv-IVb首次出现在劳伦琴五大湖，导致大量鱼类死亡。它迅速传播并在基因上产生了多样化。本研究分析了VHSv-IVb在五大湖区域内，针对该组新弹状病毒特有的新型非病毒粒子（Nv）基因，与其糖蛋白（G）、磷蛋白（P）和基质（M）基因相关的时间和空间突变模式。结果表明，Nv基因进化最快（k = 2.0×10⁻³替换/位点/年），G基因进化速度约为其1/7（k = 2.8×10⁻⁴）。在鉴定出的12种独特的Nv单倍型中，大多数（除一种外）编码不同的氨基酸，总共发生了26处变化。在12种相应的G基因单倍型中，有7种在氨基酸上有所不同，总共发生了8处变化。P基因和M基因在进化上更为保守，进化速度仅约为Nv基因的1/15（k = 1.2×10⁻⁴）。这12个分离株包含4种P基因单倍型，有两处氨基酸变化，以及6种M基因单倍型，有三处氨基酸差异。一些分离株的基因之间进化变化模式一致，但在其他分离株中则表现为独立。在2006年的大规模疫情爆发后发现了新的病毒变体；这种分化可能是对鱼类种群产生抗性的一种反应，值得进一步研究。我们于2012年从伊利湖中部没有典型VHSv症状的鱼类中分离出两种变体，它们具有独特的Nv、G和M基因序列（其中一种在P基因上也有所不同）；它们因G基因的一处氨基酸变化而彼此不同，并且因一个共同的Nv基因氨基酸变化而与所有其他分离株不同。这种快速的进化分化可能使新的病毒变体逃避鱼类宿主的识别和免疫反应，有助于其长期存在并扩展到新的地理区域。
