Genome architecture changes and major gene variations of Andrias davidianus ranavirus (ADRV)

Abstract

Ranaviruses are emerging pathogens that have led to global impact and public concern. As a rarely endangered species and the largest amphibian in the world, the Chinese giant salamander, Andrias davidianus, has recently undergone outbreaks of epidemic diseases with high mortality. In this study, we isolated and identified a novel ranavirus from the Chinese giant salamanders that exhibited systemic hemorrhage and swelling syndrome with high death rate in China during May 2011 to August 2012. The isolate, designated Andrias davidianus ranavirus (ADRV), not only could induce cytopathic effects in different fish cell lines and yield high viral titers, but also caused severely hemorrhagic lesions and resulted in 100% mortality in experimental infections of salamanders. The complete genome of ADRV was sequenced and compared with other sequenced amphibian ranaviruses. Gene content and phylogenetic analyses revealed that ADRV should belong to an amphibian subgroup in genus Ranavirus, and is more closely related to frog ranaviruses than to other salamander ranaviruses. Homologous gene comparisons show that ADRV contains 99%, 97%, 94%, 93% and 85% homologues in RGV, FV3, CMTV, TFV and ATV genomes respectively. In addition, several variable major genes, such as duplicate US22 family-like genes, viral eukaryotic translation initiation factor 2 alpha gene and novel 75L gene with both motifs of nuclear localization signal (NLS) and nuclear export signal (NES), were predicted to contribute to pathogen virulence and host susceptibility. These findings confirm the etiologic role of ADRV in epidemic diseases of Chinese giant salamanders, and broaden our understanding of evolutionary emergence of ranaviruses.

Virus genomes and virus-host interactions in aquaculture animals

“…(x) Common midwife toad ranavirus is a toad ranavirus responsible for an outbreak of a systemic hemorrhagic disease that caused high mortality in toads from northern Spain [51]. (xi) Andrias davidianus ranavirus (ADRV), the first sequenced ranavirus, is associated with high mortality in Chinese giant salamanders [52]. This ranavirus causes high mortality in wild and farmed Chinese giant salamanders [52,53].…”

“…(xi) Andrias davidianus ranavirus (ADRV), the first sequenced ranavirus, is associated with high mortality in Chinese giant salamanders [52]. This ranavirus causes high mortality in wild and farmed Chinese giant salamanders [52,53]. (xii) ADRV-2, another ranavirus strain isolated from Chinese giant salamanders after ADRV, shares a high level genome identity with ADRV [54].…”

“…The amphibian subgroup includes ADRV, Common midwife toad ranavirus, RGV, Frog virus 3, TFV, and Ambystoma tigrinum virus, while the fish subgroup comprises Epizootic hematopoietic necrosis virus, European sheatfish virus, Grouper iridovirus, and Singapore grouper iridovirus [52]. From extensive analysis of the genome architectures and major genes of this diverse array of ranaviruses (especially ADRV and RGV genomes), we have proposed a hypothetical evolutionary model for ADRV [52]. In this model, ADRV is proposed to emerge (with its current genome) from a common ancestor of the amphibian ranavirus subgroup through changes in its genome architecture and variations in some of its major virulence-related genes (Figure 1).…”

“…In this model, ADRV is proposed to emerge (with its current genome) from a common ancestor of the amphibian ranavirus subgroup through changes in its genome architecture and variations in some of its major virulence-related genes (Figure 1). This hypothesis is based on the architectural changes observed in current ranavirus genomes; these include segment inversion, fragment insertion and deletion, and several variations in major genes, such as high diversification in two duplicate genes encoding the US22 family-like proteins, truncated domains in the virulence-related gene encoding vIF2α, and the appearance of novel genes with nuclear localization signal and nuclear export signal motifs [52]. Therefore, our current model provides possible routes leading to evolutionary genetic change and crossspecies transmission mechanisms in this diverse range of ranaviruses.…”

Complete genome sequence and architecture of crucian carp Carassius auratus herpesvirus (CaHV)

“…CaHV was isolated from livers, spleens and kidneys from diseased fish according to a previously reported procedure [16]. The CaHV genomic DNA of purified viral particles was prepared by phenol-chloroform extraction as described [17]. CaHV genome sequencing was commercially performed by SinoGenoMax Co., Ltd (Beijing, China).…”