Genetically similar VHSV isolates are differentially virulent in olive flounder Paralichthys olivaceus

Abstract

Two viral hemorrhagic septicemia virus (VHSV) isolates, VHSV-KR-CJA and VHSV-KR-YGH, were isolated from viral hemorrhagic septicemia disease outbreaks in flounder farms in South Korea. The VHSV-KR-CJA isolate was isolated from a flounder farm with high mortality (80%), while the VHSV-KR-YGH isolate was isolated from a flounder farm with low mortality (15%), suggesting that these isolates differ in virulence. The virulence of these isolates was evaluated in juvenile flounder via intraperitoneal injection. Consistent with their virulence in the field, mortality data revealed that the VHSV-KR-CJA isolate was highly pathogenic (cumulative mortality of 80%), while the VHSV-KR-YGH isolate was less pathogenic in flounder (cumulative mortality of 20%). To characterize the genotypes of these viruses, the full open reading frames (ORFs) encoding nucleoprotein N, phosphoprotein P, matrix protein M, glycoprotein G, nonstructural viral protein NV, and polymerase L of these viruses were sequenced and analyzed. Sequence analysis revealed that both isolates are genetically very similar (identical amino acid sequences for P, M, NV, and L and > 99.7 and 99.8% amino acid sequence identity for N and G, respectively). Phylogenetic analysis indicated that both of these viruses belong to the Genotype IVa group, suggesting that they originated from a common ancestral virus. The low pathogenicity VHSV strain may potentially evolve to become a more pathogenic strain through only a few nucleotide substitutions. Further functional analyses of mutations in VHSV genes are necessary to identify factors that determine VHSV pathogenicity in flounder. KEY WORDS: Viral hemorrhagic septicemia virus · VHSV · Virulence · Flounder Resale or republication not permitted without written consent of the publisherDis Aquat Org 101: [105][106][107][108][109][110][111][112][113][114] 2012 Phylogenetic analyses of the N-and G-encoding genes of VHSV have identified 4 main genotypes (I to IV), with several subgroups within Genotypes I (minimum Ia to Ie) and IV (IVa and IVb) (Snow et al. 1999, Einer-Jensen et al. 2004, Lumsden et al. 2007). These genotypes reflect a largely geographic rather than a species-specific distribution. Genotype I includes a wide range of viruses originating from freshwater rainbow trout farms in continental Europe (Thiéry et al. 2002, Einer-Jensen et al. 2004) and a large number of isolates originating from marine species in the Baltic Sea, Skagerrak, Kattegat, and English Channel (Dixon et al. 1997, Einer-Jensen et al. 2004, Snow et al. 2004. Genotype II includes a limited number of VHSV isolates recovered from the Baltic Sea (Snow et al. 2004). Genotype III includes isolates from the North Sea (Einer-Jensen et al. 2004, Snow et al. 2004, North Atlantic (López-Vázquez et al. 2006), and from seawater-reared rainbow trout in western Norway (Dale et al. 2009). Genotype IV consists of viruses from the Pacific coast and Atlantic coast of North America as well as isolates from the Great Lakes region of North America and from ...

Modifications of the nucleoprotein of viral haemorrhagic septicaemia virus showed gain of virulence in intraperitoneally infected rainbow trout

“…Previous analysis byPanzarin et al (2020) showed an increased frequency of the presence of either R (arginine) or K in this position in high-virulent VHSV isolates. In terms of virulence, both rVHSV-SE9C-3592F1 and rVHSV G46K showed 50% survival in the IP infection trial corroborating the earlier suggestions that only few alterations are necessary to impact VHSV virulence Cho et al (2012). have identified that two VHSVs isolated from farmed olive flounder (Paralichthys olivaceus) in Korea (genotype IVa) with different virulence phenotypes were very similar genetically, concluding that the low-virulent VHSV could potentially evolve into higher virulence with few amino acid exchanges.…”

The Nucleoprotein and Phosphoprotein Are Major Determinants of the Virulence of Viral Hemorrhagic Septicemia Virus in Rainbow Trout

“…Extensive surveys in European waters also revealed a large VHSV reservoir in diverse marine fish (21). In the Asian Pacific Ocean, VHSV has caused disease outbreaks in cultured olive flounder (Paralichthys olivaceus) since 1996, and it is enzootic in wild marine flounder (22,23). In 2005, VHSV emerged in the Great Lakes region of the North America, causing infection and major mortality events in several freshwater fish species (24)(25)(26)(27)(28).…”

Isolation and Infectious Temperature Optimization of Genetically Similar VHSV Isolates in Farmed Olive Flounder, Paralichthys olivaceus

“…On the other hand, Genogroup IV includes isolates from the Pacific Ocean (North American, Japanese, Korean isolates). Genetically similar VHSV isolates from flounder farms in the southern part of Korea revealed greater pathogenicity than the Jeju isolates (Cho et al, 2012). Other fish viruses from flounder farms in Korea include infectious hematopoietic necrosis virus (IHNV; Park et al, 1993;Kim et al, 2007), infectious hematopoietic necrosis virus (HIRRV; Kim et al, 2005), marine birna virus (Sohn et al, 1995), beta nodavirus (Cha et al, 2007), and iridovirus (Do et al, 2005).…”