Shao P. Weng

Molecular epidemiology and phylogenetic analysis of a marine fish infectious spleen and kidney necrosis virus-like (ISKNV-like) virus.

SummaryInfectious spleen and kidney necrosis virus-like (ISKNV-like) virus causes a serious systemic disease with high morbidity and mortality of freshwater and marine fishes. Based on the ISKNV putative major capsid protein (MCP), the vascular endothelial growth factor (VEGF), the mRNA capping enzyme (Capping), and the tumor necrosis factor receptor-associated protein (TNFR) genes, primers were designed and used in PCR to determine the host range of ISKNV-like viruses. From the sampling of >1600 marine fishes representing 6 orders, 25 families, and 86 species collected in the South China Sea, 13 cultured fish species (141 fish) and 39 wild fish species (102 fish) were confirmed hosts of ISKNV-like viruses. The average percentage of infection of ISKNV-like viruses was 14.6%. The results from phylogenetic analysis of these genes revealed that ISKNV-like viruses could be placed into two clusters: cluster I was more related to ISKNV; cluster II included OSGIV (orange-spotted grouper iridovirus) and RBIV (rock bream iridovirus), and was quite different from ISKNV. The results of this study can contribute to the prediction and prevention of ISKNV disease outbreaks.

Experimental transmission, pathogenicity and physical–chemical properties of infectious spleen and kidney necrosis virus (ISKNV)

The pathogenicity of infectious spleen and kidney necrosis virus (ISKNV) was examined by infection trials in the first known host species, the mandarinfish, Siniperca chuatsi, and in 20 other teleosts cultured in China. Mandarinfish and large-mouth bass, Micropterus salmoides, were highly susceptible to infection after intraperitoneal infection of ISKNV in spleen and kidney materials from infected fish. ISKNV did not induce mortality in grass carp (Ctenopharyngodon idella), but histopathological studies revealed that they might be infected by both bathing and intraperitoneal infection. No deaths, clinical or histopathological signs were found in the 18 other species exposed by immersion or injection. Experimental infection studies showed that ISKNV infection in mandarinfish could be transmitted from infected to healthy fish through contaminated water. ISKN only occurred in mandarinfish cultured at temperature above 20°C. The resistance of the virus to treatment with disinfectants, high and low pH and UV irradiation, as well as storage at selected temperatures was assessed.

Infections of nervous necrosis virus in wild and cage-reared marine fish from South China Sea with unexpected wide host ranges

The concerns about the impact of the nervous necrosis virus (NNV) infections in wild fish have been raised. This paper presents the results of quarterly surveys of NNV in wild and cage-reared marine fish from South China Sea. Samples of 892 wild fish belonging to 69 species and 381 cage-reared fish belonging to 11 species were collected and were detected by seminested PCR and nested PCR. In the case of seminested PCR, the positive signal was detected in 3.0% and 3.1% samples of wild and cage-reared fish, respectively. However, by nested RT-PCR, the positive signal was observed in 42.3% and 63.0% samples of wild and cage-reared fish, respectively. If the fish species were considered, the positive signal was detected in 21.7% and 72.7% species of wild and cage-reared fish by seminested PCR assay, respectively. However, by nested RT-PCR, the positive signal was observed in 65.2% and 100% species of wild and cage-reared fish, respectively. The nucleotide sequences of the nested PCR products were determined. Phylogenetic tree showed that all the obtained viral isolates belonged to the red-spotted grouper nervous necrosis virus (RGNNV) genotype. Thirty-five species of the marine fish were the new hosts of NNV.