A new species of nucleo-cytoplasmic large DNA virus (NCLDV) associated with mortalities in Manitoba lake sturgeon Acipenser fulvescens

Abstract

A newly discovered virus, Namao virus, associated with morbidity and mortality, was detected among juvenile lake sturgeon Acipenser fulvescens being propagated by a conservation stocking program for this endangered species in Manitoba, Canada. The outbreaks resulted in cumulative mortalities of 62 to 99.6% among progeny of wild Winnipeg River or Nelson River lake sturgeon and occurred at 2 geographically separate facilities. Namao virus was detected in almost 94% of the moribund or dead lake sturgeon according to a conventional polymerase chain reaction (cPCR) test that is based upon amplification of a 219 bp fragment of the virus major capsid protein (MCP). The virus itself was large (242 to 282 nm) and icosahedral-shaped with 2 capsids and a condensed bar-shaped core. It was found in virus factories within the host cell cytoplasm and displayed a tropism for the integument. Namao virus caused cellular changes characterized by enlarged eosinophilic epithelial cells in the gills and skin. Samples suspected of containing Namao virus did not have cytopathic effects on primary lake sturgeon or established white sturgeon cell lines. However, viral nucleic acid was detected in the former after prolonged incubation periods. Using primers designed from conserved regions of the MCP from NCLDVs, an estimated 95 to 96% of the Namao virus MCP open reading frame was captured. Phylogenetic analysis using the MCP of Namao virus and 27 other NCLDVs suggested that Namao virus and white sturgeon iridovirus share a common evolutionary past and might be members of the family Mimiviridae or a new, as yet unrecognized, virus family. KEY WORDS: Namao virus · Mimiviridae · Endangered speciesResale or republication not permitted without written consent of the publisher

Molecular identification of iridoviruses infecting various sturgeon species in Europe

“…The primers described by Clouthier et al . () were also included on the map (italics) for comparison. The short variable sequence of 4‐nucleotides is indicated by a triangle (see text).…”

“…More recently, a new iridovirus named Namao virus (NV) has been found in the lake sturgeon species ( A. fulvescens ) in restocking facilities in Canada (Clouthier et al . ). The presence of this virus is correlated with high mortality in this species.…”

“…Furthermore, there is a surprising genetic link between the MCP genes of NV and the Cafeteria roenbergensis virus, a virus from the Mimiviridae family, very distant biologically and taxonomically (Clouthier et al . ). Therefore, the exact classification of these sturgeon viruses as well as their precise genetic relations awaits more sequencing data.…”

Structure of large dsDNA viruses

“…Applying this criterion excluded many large viruses from metagenomic studies. During the last two decades the application of less stringent isolation techniques and improvements of isolation protocols for viruses infecting amoeba (Pagnier et al, 2013) have led to the discovery of many large viruses, especially in aquatic environments (Ghedin and Claverie, 2005; Boyer et al, 2009; Fischer et al, 2010; Thomas et al, 2011; Aherfi et al, 2013; Clouthier et al, 2013). In combination with improvements in sequencing technologies such as pyrosequencing, this allows for fast and effective analysis of the large genomes associated with these viruses and their subsequent classification based on similarities of genetic markers.…”

Ultrastructural morphogenesis of a virus associated with lymphocystis-like lesions in parore Girella tricuspidata (Kyphosidae: Perciformes)

“…The nucleo-cytoplasmic large DNA viruses (NCLDV) comprise the families Poxviridae, Asfar viridae, Iridoviridae, Phycodnaviridae, Mimiviridae, Ascoviridae and Marseilleviridae (Salas & Andrés 2013) of the superfamily Megavirales (Clouthier et al 2013, Piégu et al 2015. The Iridoviridae comprise 5 genera: Ranavirus infecting poikilothermic vertebrates (Chinchar 2002, Whittington et al 2010, Chinchar & Waltzek 2014, Peng et al 2015; Megalocytivirus (Kurita & Nakajima 2012) causing systemic infections in fish (Inouye et al 1992, Subramaniam et al 2012, Sriwanayos et al 2013; Lymphocystivirus usually causing superficial disease (skin, fins) of fish, particularly flatfish (Pleuronectiformes) (Chinchar et al 2009, Yan et al 2011; and Iridovirus and Chloriridovirus infecting insects.…”