Surveillance of emerging fish viral pathogens in some Southeast Asian countries

Preventing the transboundary movement of fish viral pathogens in a global environment requires active surveillance. This study examined the presence of three emerging viral pathogens among koi, common, grass, and silver carp in Cambodia, Lao PDR, Myanmar, Philippines, and Vietnam. The studied viruses included koi herpesvirus (KHV), spring viremia of carp virus (SVCV), and grass carp reovirus (GCRV). Detection methods consisted of virus isolation by cell culture, infection assay in naive fish, polymerase chain reaction (PCR), and reverse-transcriptase PCR (RT-PCR). Tissues were collected and pooled from 193 fish samples in Dec. 2004 to Feb. 2005, 406 in Sep. 2005 to Feb. 2006, and 1302 in Oct. 2006 to Feb. 2007. For cell culture, tissue filtrates were prepared from pooled spleens, kidneys, livers, and gills and inoculated onto koi fin (KF-1), grass carp kidney (GCK), and fat head minnow (FHM) cells. For infection assay, tissue filtrates were injected intraperitoneally to healthy, naive common carp. No virus was detected after three cell culture passages and the infection bioassays. One-step and nested-step PCR was used to detect KHV in gills of fish samples. One-step and semi-nested RT-PCR was used to detect SVCV and GCRV in the spleens, kidneys, and livers of fish samples. Samples from all three years from all five countries yielded negative results for all three viruses, indicating that KHV, SVCV, and GCRV were not present in these five countries during the period of the study although KHV outbreaks had been detected in Indonesia, Taiwan, Japan, Thailand, China, and Malaysia.Appreciation is due to SEAFDEC-AQD and the Japanese Trust Fund for research funding, to Drs. Joebert Toledo, Rolando Platon, Hiroshi Ogata, Koichi Okuzawa, Kazuya Nagasawa, and Junichiro Okamoto for support and encouragement, to Drs. R. Hedrick/M. Sano, Y.L. Jiang, and A. Goodwin for the cell lines and viruses, and to N.D. Nguyen, T.C. Tran, P. Thu, and L.V. Khoa (Vietnam), T. Thongphoun and P. Xayasong (Lao PDR), B. Racy, P. Tach, and T. Chea (Cambodia), M.M. Htwe, N.N. Aye, T.W. May (Myanmar), J. Somga, T. Cuyos, M. Navarce (Philippines), and Eleonor Tendencia for assistance/coordination during samplings