What is KHV?

KHV (Koi herpesvirus) is a highly contagious viral disease which was first reported in 1998, after the outbreak in Israel. However, analysis of archived materials indicated that a koi farm in the United Kingdom was infected by KHV in 1996. Since then,
KHV has been found in most countries that cultivate common carp and/or koi. The world organization for animal health (OIE) has listed KHV as a serious reportable disease since 2006.
The koi herpesvirus only attacks koi and common carp. That means the virus has no impact on other fish species, or on humans who eat the infected fish. The reason that this disease scares hobbyists and aquaculture farmers is that KHV often causes more than 80% to nearly 100% mortality in both fries and adult carp.

Some researchers recognized this unknown virus had similar shape and characters as other herpes viruses. Based on morphology and the sequential development in the host cell nucleus, the new virus was designated as koi herpesvirus. On the other hand, based on the finding of exceptional large size of dsDNA and distinct DNA sequences in KHV, it was once called as “carp interstitial nephritis and gill necrosis virus” (abbreviated as CNGV) by Ilouze et al. to reflect its clinic symptoms shown in infected fish. The dispute on designation was subsided when Waltzek et al. found the most convincing evidence to group KHV within the Herpesvirus family in 2005. KHV genome encodes several genes closely related to homology in two known cyprinid herpsviruses, namely carp pox virus (Cyprinid herpesvirus-1, CyHV-1) and hematopoietic necrosis herpesvirus (CyHV-2). Together with previous morphological and biological description, KHV officially became the third member (CyHV-3) of Cyprinid herpesviruses.

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Waltzek T. B., Kelley G. O., Stone D. M., Way K., Hanson L., Fukuda H., Hirono I., Aoki T., Davison A. J., and Hedrick R. P. (2005). Koi herpesvirus represents a third cyprinid herpesvirus (CyHV-3) in the family Herpeviridae. Journal of General Virology, vol. 86, 1659–1667