Isolation and identification of genogroup Ⅰ and genogroup Ⅴ infectious pancreatic necrosis virus strains
DUAN Kaiyue, ZHAO Jingzhuang, REN Guangming, SHAO Yizhi, LU Tongyan, HE Baoquan, XU Liming
1.National Demonstration Centre for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai 201306, China; 2.Heilongjiang River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Harbin 150070, China; 3.National Pathogen Collection Center for Aquatic Animals, Shanghai Ocean University, Shanghai 201306, China; 4.Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223, China
Abstract: To find the pathogens causing persistent death of juvenile fish from a rainbow trout Oncorhynchusmykiss farm in the northwest China, the viruses often infecting salmon and trout were identified by histopathological observation and molecular identification methods, and the genotype analysis, virus particles microscopic structure observation and virulence characteristics of the isolated virus were analyzed by phylogenetic analysis, electron microscopic observation, virus titer detection and artificial infection test. The results showed that cell necrosis with cavitation and lysis were widely distributed in the liver, spleen and kidney of the diseased fish, and typical cytopathic effects were observed in the tissue homogenate infected with CHSE-214 cells. Three infectious pancreatic necrosis virus (IPNV) strains were isolated from different regions of the farm, in which the isolates IPNV-F1 and IPNV-W2 belonged to genogroup Ⅰ, with the maximal homology with Chinese IPNV strains WZ2016 (KX355401) and ChRtm213 (KX234591), and VP2 gene sequences identify was 100% in WZ2016 (KX355401) and 98.5% in ChRtm213 (KX234591). The isolate IPNV-W1 belonged to genogroup Ⅴ and had the maximal homology with Italy isolate IPNV/ rainbow trout/I/PN/208/Mar88 (MG543567), VP2 gene sequences identify of 99.1%. The virion, without capsule membrane and with crystalline arrangement, was observed in CHSE-214 cells, and the mean titer of three IPNV isolates in CHSE-214 cell lines was tissue culture infective dose 107.43TCID50/0.1 mL (IPNV-F1), 107.30 TCID50/0.1 mL (IPNV-W1) and 107.29 TCID50/0.1 mL (IPNV-W2), respectively. The juvenile rainbow trout were intraperitoneally injected with each IPNV isolate at a dose of 0.1 mL per fish, without death within 60 days post challenge. The mean titer of IPNV isolates in tissues 30 days after challenge were found to be 104.50 TCID50/0.1 g tissue (IPNV-F1), 105.38 TCID50/0.1 g tissue (IPNV-W1) and 104.13 TCID50/0.1 g tissue (IPNV-W2), respectively. On the 60 days post challenge, the mean titer of IPNV in tissues was declined to 103.43 TCID50/0.1 g tissue (IPNV-F1), 104.50 TCID50/0.1 g tissue (IPNV-W1) and 103.21 TCID50/0.1 g tissue (IPNV-W2), respectively. It was found that there were co-existance of genogroup I and genogroup V IPNV strains in the rainbow trout farm. The isolated IPNV strains here belonged to different genotypes within one fish farm for the first time, which will provide reference with the prevention and control of IPN in China.
2021, Vol. 36 
