Scientists sequence KHV strain genomes

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An international team of scientists has sequenced the complete genomes of three different strains of the deadly fish virus KHV.

Virologists from Japan, Israel and the USA worked together to publish the study which is the first to compare the viral genes of the Israeli, Japanese and USA strains of the virus.

The paper, which is due to be published shortly in the Journal of Virology, says that the virus (now officially known as Cyprinid Herpes Virus III) has a 295 kbp genome, making it the largest so far recorded in the family Herpesviridae.

Some 15 genes found in the KHV genomes have clear homologs (genetic equivalents) in the distantly related channel catfish virus Ictalurid Herpes Virus I, which the experts say confirms its placement within the Herpesviridae.

The authors wrote: "The three strains were interpreted as having arisen from a wild type parent encoding 156 unique protein-coding genes, eight of which are duplicated in the terminal repeat.

"In each strain, four to seven genes from among a set of nine are fragmented by frameshifts likely to render the encoded proteins non-functional.

"Six of the affected genes encode predicted membrane glycoproteins. Frameshifts or other mutations close to the 3'-ends of coding sequences were identified in a further six genes.

"The conclusion that at least some of these mutations occurred in vivo prompts the hypothesis that loss of gene functions might be associated with emergence of the disease, and provides a basis for further investigations into the molecular epidemiology of the virus."

For more information see the paper: Aoki T, Hirono I, Kurokawa K, Fukuda H, Nahary R, Eldar A, Davison AJ, Waltzek TB, Bercovier H, Hedrick RP (2007) - Genome sequences of three koi herpesvirus isolates representing the expanding distribution of an emerging disease threatening koi and common carp worldwide. Journal of Virology. In press.