Megalocytivirus infection in fish

Section: Discussionmentioning

confidence: 99%

Detection of infectious spleen and kidney necrosis virus (ISKNV) and turbot reddish body iridovirus (TRBIV) from archival ornamental fish samples

Go¹,

Waltzek²,

Subramaniam³

et al. 2016

“…Megalocytiviruses have been studied extensively due to their ability to cause significant disease across a wide range of cultured freshwater and marine species (Kurita & Nakajima 2012, Subramaniam et al 2012). Here we describe the first case of megalocytivirus infection in cultured Nile tilapia fingerlings based on pathologic and genetic evidence.…”

Section: Resale or Republication Not Permitted Without Written Consenmentioning

confidence: 99%

Megalocytivirus infection in cultured Nile tilapia Oreochromis niloticus

Subramaniam

Gotesman²,

Smith³

et al. 2016

Megalocytiviruses, such as infectious spleen and kidney necrosis virus (ISKNV), induce lethal systemic diseases in both ornamental and food fish species. In this study, we investigated an epizootic affecting Nile tilapia Oreochromis niloticus cultured in the US Midwest. Diseased fish displayed lethargy, gill pallor, and distension of the coelomic cavity due to ascites. Histopathological examination revealed a severe systemic abundance of intravascular megalocytes that were especially prominent in the gills, kidney, spleen, liver, and intestinal submucosa. Transmission electron microscopic examination revealed abundant intracytoplasmic polygonal virions consistent with iridovirus infection. Comparison of the full-length major capsid protein nucleotide sequences from a recent outbreak with a remarkably similar case that occurred at the same facility many years earlier revealed that both epizootics were caused by ISKNV. A comparison of this case with previous reports suggests that ISKNV may represent a greater threat to tilapia aquaculture than previously realized. KEY WORDS: Iridoviridae · Megalocytivirus · Infectious spleen and kidney necrosis virus · Aquaculture · Ornamental fish Resale or republication not permitted without written consent of the publisherDis Aquat Org 119: [253][254][255][256][257][258] 2016 Although tilapia are considered relatively resistant to disease, they are susceptible to common aquatic pathogens (e.g. viruses, bacteria, fungi, water molds, parasites) when reared intensively. The primary microbial pathogens affecting cultivated tilapia include Gram-negative bacteria (Aeromonas hydrophila, Flavobacterium columnare, and Francisella noatunensis), Gram-positive bacteria (Streptococcus spp.), and water molds such as members of the family Saprolegniaceae (e.g. Achyla and Saprolgenia spp.; Plumb & Hanson 2010). Despite the global culture of tilapia, few viruses have been described from tilapia, and none has proven to be a serious threat to the industry (El-Sayed 2006).The first RNA virus discovered in tilapia was an aquabirnavirus isolated from apparently healthy Mozambique tilapia O. mossambicus cultured in Lukang, Taiwan (Hedrick et al. 1983). In 2007, a betanodavirus was detected by RT-PCR in Nile tilapia larvae following a mass mortality event at a western European fish farm (Bigarré et al. 2009), andEyngor et al. (2014) isolated a novel RNA virus (tilapia lake virus) from wild tilapia and confirmed its pathogenicity via experimental infection in Nile tilapia.The first DNA viruses discovered in tilapia were iridoviruses. Although the family Iridoviridae is composed of 5 genera, only members of the genera Megalocytivirus, Lymphocystivirus, and Ranavirus infect fish (Zhang & Gui 2015). Paperna (1973) detected lymphocystis virus in tilapine and haplochromine cichlids from the Rift Valley Lakes Kitangiri and Victoria. A severe (100% mortality) epizootic among Mozambique tilapia fry held in an Australian aquatic disease laboratory was tentatively attributed to a ranavirus, Bohle ir...

“…It cannot be assumed that the virus reported here was an LCDV, as ranaviruses (Pozet et al 1992, Bayley et al 2013, Chinchar & Waltzek 2014, George et al 2015 and megalocytiviruses (Subramaniam et al 2012, Waltzek et al 2012) also infect fish, are very non-host specific (Mao et al 1997, Hyatt et al 2000, Bayley et al 2013, and a single host genus such as grouper (Epinephalus) may be infected with ranavirus (Peng et al 2015) and LCDV (Huang et al 2015). Geographic occurrence rather than host group specificity may be as important in determining which host groups are infected (Mao et al 1997, Hyatt et al 2000, Bayley et al 2013.…”

Section: Discussionmentioning

confidence: 88%

“…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. In general, iridovirids and asfarivirids undergo DNA replication in the nucleus, followed by a second round of cytoplasmic DNA replication in perinuclear, often lucent, viromatrix (Zupanovic et al 1998, Huang et al 2006, Chinchar & Waltzek 2014 or viral factories (Salas & Andrés 2013) in which scattered icosahedral virions form, that become cytoplasmic paracrystalline arrays of mature virions (Zupanovic et al 1998, Majji et al 2006.…”

Section: Introductionmentioning

confidence: 99%

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

Hine¹,

Wakefield²,

Mackereth³

et al. 2016

The morphogenesis of large icosahedral viruses associated with lymphocystis-like lesions in the skin of parore Girella tricuspidata is described. The electron-lucent perinuclear viromatrix comprised putative DNA with open capsids at the periphery, very large arrays of smooth endoplasmic reticulum (sER), much of it with a reticulated appearance (rsER) or occurring as rows of vesicles. Lysosomes, degenerating mitochondria and virions in various stages of assembly, and paracrystalline arrays were also present. Long electron-dense inclusions (EDIs) with 15 nm repeating units split terminally and curled to form tubular structures internalising the 15 nm repeating structures. These tubular structures appeared to form the virion capsids. Large parallel arrays of sER sometimes alternated with aligned arrays of crinkled cisternae along which passed a uniformly wide (20 nm) thread-like structure. Strings of small vesicles near open capsids may also have been involved in formation of an inner lipid layer. Granules with a fine fibrillar appearance also occurred in the viromatrix, and from the presence of a halo around mature virions it appeared that the fibrils may form a layer around the capsid. The general features of virogenesis of large icosahedral dsDNA viruses, the large amount of ER, particularly rsER and the EDIs, are features of nucleo-cytoplasmic large DNA viruses, rather than features of 1 genus or family.