Detection of koi herpesvirus (KHV) in cyprinius carpio (KOI) stocks using enzyme-linked immunosorbent assay (ELISA)

Koi herpesvirus (KHV), which is also known as Cyprinid herpesvirus 3 (CyHV-3) infection, is an OIE (international des epizootis) listed disease that caused high losses in common and koi carp in Indonesia and Japan in 2002 and 2003. Since the mid of 2006, the polymerase chain reaction (PCR) has been used in Malaysia for surveillance of koi fingerlings to detect virus nucleic acid, but it has been found to produce unreliable results. Following this, an alternative enzyme-link immunosorbent assay (ELISA) technique for the detection of antibody against KHV was used to find evidence of KHV infection in koi carp stocks on farms that had been sampled for the PCR. For this purpose, a total of 245 serum samples from koi carp stocks were collected and tested for the antibody to KHV by the ELISA at the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) laboratory, Weymouth, UK. Two hundred and eight samples were found to be negative but 37 others were either definitely positive or close to borderline positive and all were retested. The final results showed that 222 (90%) samples were confirmed as negative and 19 (8%) others were definitely positive. Meanwhile, four samples (1.6%) were positive at dilutions of 1:400 or 1:200, but cross reactions with CyHV-1 (causing herpesviral epidermal hyperplasia) could have occurred at those dilutions. Three of the samples were the only positive fish at two sites, but the fourth sample came from a site at which there were 4 definite positive samples (from 20 fish sampled). Thus this study confirmed that Malaysian koi stocks have previously been exposed to KHV. With the lack of bio-security measures and awareness, there was a high probability that the koi carp had been exposed to KHV, leading to subclinical infections and some fish might possibly have become carriers of the virus. Hence, further surveillance needs to be conducted to determine the true situation of the KHV infection in Malaysia