First report on the occurrence of cyprinid herpesvirus 3 in koi carp (Cyprinus carpio koi) in India.

This study reports the occurrence of cyprinid herpesvirus 3 (CyHV-3) in koi carp (Cyprinus carpio koi) for the first time in India. The koi carp, with clinical signs of ulcer with haemorrhage on body surface, necrosis of fin and discolouration of gill associated with huge mortality, were observed in aquarium shops, rearing tanks and grow-out ponds located in Chennai, India. The PCR assay carried out on infected fish samples using different primer sets specific to CyHV-3 confirmed its presence in the infected fish. Sequence analysis of partial thymidine kinase gene revealed 100% similarity with the sequence of CyHV-3 available in GenBank. Cell lines of koi carp and catla were found to be susceptible to CyHV-3 and its replication was confirmed by viral-specific cytopathic effect, PCR and bioassay. The CyHV-3 infection was reproduced by intramuscular injection of inoculum prepared from CyHV-3-infected fish to satisfy Koch's postulates. Tissue tropism of CyHV-3 in infected fish by PCR assay revealed the presence of CyHV-3 in all vital organs with prominent band in gill and gut tissue.