| Pathogenic Aeromonas hydrophila is reported to be a major aquatic animal pathogens which could cause aquatic animals infectious and outbreaking disease. For clarify A. hydrophila epidemiology in East China, A. hydrophila epidemiology was investigated with combination of traditional epidemiological investigation methods and molecular biology techniques in this artical. Main studies are as following aspects.Epidemiological investigation of A. hydrophila-related diseases of main kinds of freshwater fishes were carried out in 11 experimental locations of East China respectively during April to November in 2009. Afterwards, the application of duplex PCR methed on identification of these strains of aquatic animal pathogens was studied. The results suggested that A. hydrophila could be founded in every month during April to November. Incidence of related disease was 73% and occurred with peak on July to September. The average mortality rate varied from 20% to 30%. It most affected breams and crucian carps. The epidemic of A. hydrophila was largely attributed to the mass multiplication of A. hydrophila at high temperature on summer and early autumn, the high-density aquaculture and the deterioration of water environment.35 pathogenic A. hydrophila strains identificated by duplex PCR method were examined by using antisera for two serotypes of O:5 and O:9 which prepared by tipical strains named BSK-10 and TPS-30. The results suggested that there were 5 isolates belong to serotype O:5, 12 isolates belong to serotype O:9, while others neither serotype O:5 nor serotype O:9. Serotypes of O:5 and O:9 was a widespread representative found in Zhejiang, Jiangsu and Anhui provence and isolated from many kinds of freshwater fishes such as Breams, Crucian carps, Silver carps, and so on. In comparison, these two serotypes were more well-informed on summer and autumn, while there were more A. hydrophila-related disease infecting and outbreaking.The application of ERIC-PCR on genetyping of these pathogenic A. hydrophila strains of aquatic animal pathogens was studied. ERIC-PCR pattern of 35 strains upon cluster analysis at the level of 10 generated five different groups called ERIC groups and were designated as E1 to E5. And E1 (n=16) included 45.71% of all strains and had complex hosts and area sources, which showed that it would be the dominant genotyping microorganisms of the pathogenic A. hydrophila among cyprinidae fishes in East China. Besides, it could also help us to further explore the differences and connections in genetic composition between these strains isolated from different areas, different hosts or different months according to the dendrogram based on the ERIC-PCR fingerprinting. In this study, it demenstrated that pathogenic A. hydrophila strains isolated from the same or similar areas tended to show same or similar genotypes. But differences between different strains that came from different hosts were not apparent, which may be because of very close genetic relationship between host animals such as Crucian carps, Breams and Silver carps. Pathogenic strains which isolated from the same area but in different months in 2009 have even much different genetypes. It would be bringing more difficulties for prevention and conformity of the prevalence of the related disease. Compared with serotyping method, ERIC-PCR is rapid, simple, reproducible, affordable and is a highly discriminatory molecular typing method for genotyping A. hydrophila. Futhermore, it could be used to analyze its relationships and diversities in gene levels of all isolates as one of practical measures for epidemiological investigation of A. hydrophila.This study would be provided with great significance in expounding epidemiological characteristics of A. hydrophila disease of aquatic animals in East China. Besides, not only it provided a scientific support for developing more effective vaccine against A. hydrophila, but also it offered a useful tool for rapid diagnosis and epidemiological invesitigation of the pathogenic A. hydrophila.
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