Emergence of carp edema virus in cultured ornamental koi carp, Cyprinus carpio koi, in India

Abstract

A disease outbreak was reported in adult koi, Cyprinus carpio koi, from a fish farm in Kerala, India, during June 2015. The clinical signs were observed only in recently introduced adult koi, and an existing population of fish did not show any clinical signs or mortality. Microscopic examination of wet mounts from the gills of affected koi revealed minor infestation of Dactylogyrus sp. in a few koi. In bacteriological studies, only opportunistic bacteria were isolated from the gills of affected fish. The histopathological examination of the affected fish revealed necrotic changes in gills and, importantly, virus particles were demonstrated in cytoplasm of gill epithelial cells in transmission electron microscopy. The tissue samples from affected koi were negative for common viruses reported from koi viz. cyprinid herpesvirus 3, spring viraemia of carp virus, koi ranavirus and red sea bream iridovirus in PCR screening. However, gill tissue from affected koi carp was positive for carp edema virus (CEV) in the first step of nested PCR, and sequencing of PCR amplicons confirmed infection with CEV. No cytopathic effect was observed in six fish cell lines following inoculation of filtered tissue homogenate prepared from gills of affected fish. In bioassay, the symptoms could be reproduced by inoculation of naive koi with filtrate from gill tissue homogenate of CEV-positive fish. Subsequently, screening of koi showing clinical signs similar to koi sleepy disease from different locations revealed that CEV infection was widespread. To our knowledge, this is the first report of infection with CEV in koi from India.

Emergence of carp edema virus (CEV) and its significance to European common carp and koi Cyprinus carpio

“…3), anorexia, ulcers around the mouth and base of the fins, pale swollen gills (Fig. 4) and inflammation of the anal vent (Miyazaki et al 2005, Haenen et al 2014, Jung-Schroers et al 2015, Swaminathan et al 2016, Zhang et al 2017.…”

“…At higher temperatures, fish die within 2 or 3 d of first showing lethargic behaviour (Hedrick et al 1997, Miya zaki et al 2005, Jung-Schroers et al 2015, Swaminathan et al 2016. In common carp and sometimes in koi, disease outbreaks also occur during periods of low water temperatures (6−10°C), and the course of the disease is more protracted, with lower mortality (Way & Stone 2013, Lewisch et al 2015.…”

“…The virus has also been detected on koi farms in Brazil, the first detection of CEV in the Southern Hemisphere (Hesami et al 2015). Also, more recently, outbreaks of CEVD have been reported on koi farms in India and China (Swaminathan et al 2016, Zhang et al 2017.…”

Comparison of PCR methods for the detection of genetic variants of carp edema virus

“…The number of countries in which infections with CEV and outbreaks of KSD were detected in carp or koi has been rising rapidly over the last several years. Currently, the virus has been recorded in several European countries (Way & Stone 2013, Jung-Schroers et al 2015, Lewisch et al 2015, Matras et al 2017, the USA (Hedrick et al 1997), and from at least 3 countries in Asia: Japan (Oyamatsu et al 1997), India (Swaminathan et al 2016) and China (Zhang et al 2017).…”

“…Several electron microscope images have documented poxvirus-like particles in the infected gill epithelium (Miyazaki et al 2005). However, despite many attempts, the cultivation of CEV in vitro has not been successful employing the fish cell lines presently available (Jung-Schroers et al 2015, Lewisch et al 2015, Swaminathan et al 2016. Genomic data of the virus is limited to the fragment of the DNA sequence encoding the core protein P4a (Oyamatsu 1996, Matras et al 2017, but a comparison of CEV sequences retrieved from diseased fish from various locations in Europe and Asia (see Table 1, and Fig.…”