Isolation and preliminary identification of rhabdovirus from Channa maculata cultured in pond

During September, 2010, an unknown disease with highly mortality of over 80% broke out in cultured Channa maculata, at Foshan area of Guangdong province. A strain of rhabdovirus was isolated from the diseased Channa maculata. After the third passage, obvious cytopathic effect (CPE) could be observed in EPC and FHM, inoculated with the ultra-filtrate of liver, spleen and kidney from diseased fishes with no bacteria. Mass of bullet-shaped viruses which about 53 nm140 nm in size, were observed in the ultrathin sections made of infected EPC under electron microscopy. Both artificial infection for healthy Channa maculata with either filtrate of tissues or infected EPC by intraperitoneal injection caused 100% mortality. The symptoms of the infected fishes were similar to those of natural infection. This result indicated that this virus was the lethal pathogen of the fulminant disease. With the primers designed according to the conserved regions of SCRV N gene, specific products with predicted size (400 bp) were obtained from all the diseased tissues and infected cells. Comparative analysis of nucleotide sequences was performed with the GenBank databases using BLAST database network service. The results showed that the gene products shared a highest identity (i.e., 94%) with the corresponding sequence of SCRV EF575725.1. On the basis of neighbor-joining analyses of the N gene sequences, phylogenetic tree was constructed with the Clustalx and Mega 4, and it formed a single cluster with SCRV. As their sizes and symptoms of the diseased fishes had some differences, the virus in present research was named as CHRV tentatively.