Isolation and characterization of a ranavirus from koi, Cyprinus carpio L., experiencing mass mortalities in India

Abstract

We investigated mass mortalities of koi, Cyprinus carpio Linnaeus, 1758, experienced in South Indian fish farms by virus isolation, electron microscopy, PCR detection, sequencing of capsid protein gene and transmission studies. Samples of moribund koi brought to the laboratory suffered continuous mortality exhibiting swimming abnormalities, intermittent surfacing and skin darkening. Irido-like virus was isolated from the infected fish in the indigenous snakehead kidney cell line (SNKD2a). Icosahedral virus particles of 100 to 120 nm were observed in the infected cell cultures, budding from the cell membrane. Virus transmission and pathogenicity studies revealed that horizontal transmission occurred associated with mortality. PCR analysis of infected fish and cell cultures confirmed the presence of Ranavirus capsid protein sequences. Sequence analysis of the major capsid protein gene showed an identity of 99.9% to that of largemouth bass virus isolated from North America. Detection and successful isolation of this viral agent becomes the first record of isolation of a virus resembling Santee-Cooper Ranavirus from a koi and from India. We propose the name koi ranavirus to this agent.

Distribution and Host Range of Ranaviruses

“…A SCRV strain isolated from moribund hatchery-reared largemouth bass reared in China was found to be highly lethal to largemouth bass (Deng et al 2011 ); however, little or no mortality was observed in seven other species tested including koi ( Cyprinus carpio ; Table 3 ). In contrast, a recent mass mortality event among farmed koi in southern India was attributed to a strain of SCRV (George et al 2014 ), although the authors did not provide a detailed description of viral-induced pathology.…”

“…The reasons for the emergence of ranaviruses as pathogens of fi nfi sh within both natural and managed populations are unknown. However, the repeated detection of the same fi nfi sh ranaviruses (e.g., SCRV) around the globe suggests that the international movement of live animals and their products likely plays an important role in the occurrence of these epizootics (Hedrick and McDowell 1995 ;Plumb and Zilberg 1999a ;Grant et al 2005 ;Schramm and Davis 2006 ;Deng et al 2011 ;George et al 2014 ).…”

“…Recently, SCRV and FV3 have been repeatedly detected among hatchery-reared freshwater fi shes in North America and Asia (Woodland et al 2002b ;Prasankok et al 2005 ;Deng et al 2011 ;George et al 2014 ;Chinchar and Waltzek 2014 ;Waltzek et al 2014 ). Two genetically distinct but related ranaviruses, Singapore grouper iridovirus (SGIV) and grouper iridovirus (GIV), have negatively impacted grouper mariculture in Asia since the 1990s (Chua et al 1994 ;Murali et al 2002 ;Qin et al 2003 ).…”

“…It seems likely that SCRV has been disseminated across the USA and globally through the unrestricted movement of live fi sh and their products associated with the ornamental (Hedrick and McDowell 1995 ;Deng et al 2011 ;George et al 2014 ), food (Plumb and Zilberg 1999a ), and angling industries (Grant et al 2005 ;Schramm and Davis 2006 ). For example, in the USA, largemouth bass angling tournaments may contribute to the spread of SCRV to naïve fi sh by placing infected and uninfected fi sh in close proximity; however, the stress associated with angling has not been shown to greatly increase SCRV-associated mortality (Grant et al 2005 ;Schramm and Davis 2006 ).…”

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

“…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.…”