Detection and significance of koi herpesvirus (KHV) in freshwater environments

1. Koi herpesvirus (KHV) disease, a lethal disease in carp and koi, has spread rapidly since the late 1990s. Only a few studies have focused on the ecology of KHV in natural freshwater environments, although characterization and the diagnosis of KHV disease have been intensively studied. This is mainly due to the lack of reliable detection methods for KHV in natural environments. 2. Three different approaches have been used to detect KHV in fish samples: (i) isolation and identification of the virus using cultured cell lines; (ii) detection of viral DNA with target DNA amplification techniques; and (iii) detection of anti-KHV antibodies using an enzyme-linked immunosorbent assay (ELISA). Among these methods, DNA amplification techniques have become most popular because of their sensitivity and simplicity. 3. In contrast to KHV detection in fish samples, detection of KHV from water and sediment samples has not been reported. This is the result of a lack of reliable KHV concentration methods for water and sediment samples, although methodology from public health and marine microbiology may be applicable to determine KHV concentration in such samples. 4. Few reports have evaluated the environmental factors (e.g. temperature, UV irradiation) that affect the fate of KHV in water bodies. Mass mortality of wild carp caused by KHV infection would result in the removal of a large omnivorous fish from freshwater ecosystems and may thus alter community structure and ecosystem functioning.