Molecular study of Koi herpesvirus in warm-water fish farms mortality in Khuzestan province

Herpesvirus type 3 (CyHV-3) is the main cause of contagious koi herpesvirus infectious (KHVD) in common carp and koi worldwide. For this purpose, 60 pieces of common carp from farms with losses and farms from Khuzestan province that reported losses in the last few years were sampled during 2017 to 2021 for detection of Koi herpes virus disease by molecular method. In order to increase the virus load in gill and kidney tissues, three gills and kidney samples were separately mixed together for each three fish. DNA extraction from the tissue was performed using the commercial kit of Raha Zist Padtan Company according to the instructions. Afterward, Nested PCR test was performed using Amplicon master mix and polymerase gene primers. The results of the Nested PCR showed that 3 samples (two gill samples and one kidney tissue sample) out of 40 mixed samples tested had 339 kbp band and were considered as positive samples. Sequencing of PCR products and preliminary Blast analysis showed that the sequence of one of the positive samples was similar to the CyHV-3. The results of the alignment of the nucleotide rows and the phylogeny tree of this sequence confirmed Koi herpesvirus and it was registered in the World Gene Bank with the accession number of LC713276.