Koi Herpesvirus: Status of Outbreaks, Diagnosis, Surveillance, and Research

Abstract

Koi herpesvirus (KHV; Cyprinid herpesvirus 3) is a major threat to common carp and koi carp production worldwide. It is listed by the World Organization for Animal Health (OIE), and has been reported in 26 coun- tries. KHV was designated a Specific Disease by Japanese law in 2003. Japan’s National Research Institute of Aquaculture (NRIA) is a reference laboratory for the disease and conducts confirmatory diagnosis. The num- ber of disease occurrences in Japan peaked in 2004, but has been gradu- ally decreasing since then. The disease occurs mostly during spring and autumn when water temperatures are 16-28°C. In general, conventional polymerase chain reaction (PCR) is the most useful method for diagnosing KHV due to its high sensitivity, high specificity, and rapidity. More recently, real time PCR, nested PCR, and loop-mediated isothermal amplification (LAMP) were developed to diagnose the virus. Reverse transcriptase poly- merase chain reaction (RT-PCR) targets mRNA of KHV to detect the repli- cating virus. An enzyme-linked immunosorbent assay (ELISA) detects anti- KHV antibodies in carp serum of surviving infected fish and is expected to be a tool for surveillance of KHV. However, cross reactions with anti- Cyprinid herpesvirus 1 antibodies in the ELISA need to be resolved. A sys- tematic research project on development of diagnostic and prevention tech- nologies for KHV disease was conducted in 2004-2006 by the NRIA in cooperation with Japanese universities and enterprises and SEAFDEC. The fruitful results of the project are included in this review.