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Emergence of carp edema virus (CEV) in cultured ornamental koi carp, Cyprinus carpio koi in India.

Research paper by T Raja TR Swaminathan, Raj R Kumar, Arathi A Dharmaratnam, Valaparambil S VS Basheer, Neeraj N Sood, Parvatha Kumar PK Pradhan, N K NK Sanil, P P Vijayagopal, Joykrushna J Jena

Indexed on: 03 Dec '16Published on: 03 Dec '16Published in: The Journal of general virology



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 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 carps was positive for carp edema virus (CEV) in 1st step of nested PCR, and sequencing of PCR amplicons confirmed infection with CEV. No cytopathic effect (CPE) was observed in 6 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 naïve 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.

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