Epidemiological Analysis And Etiological Investigation Of Japanese Encephalitis In Anhui Province

Japanese encephalitis (JE), which is caused by Japanese encephalitis virus (JEV), is an acute vector-born Arboviral disease that impairs the central nervous system (CNS). JE is prevalent mostly in Asia and the Pacific region. JEV is mainly transmitted by mosquitoes and JE has a clearly peak incidence period between summer and fall. JE is one of the most important causes of viral encephalitis worldwide (particularly for children), with a mortality rate of30%. Approximately50%of JE patients present severe neurological and mental sequelae.China is the main region of JE endemism. Historically, JE prevalence has been high in China, where major outbreaks occurred from1960s to1970s. After the nationwide vaccination program initiated in the1970s, the number of reported cases dramatically decreased, and the incidence maintains at a lower level in recent years. However, the prevalence even outbreak of JE occasionally occurs in some certain local regions, with thousands of cases death and disability, which bring a heavy burden of disease for the social and individual family.Anhui province, which locates in the lower reaches of the Changjiang River in China, is one of the highly endemic regions of JE historically. In recent years, followed by using of JE vaccines, the incidence rate decreased but there are still hundreds of JE cases reported in Anhui province annually, and the small-scale epidemic of JE occurs in the local. Thus, it is necessary to analyze the epidemic trend of JE systematically in Anhui province in recent years, to study the status of JEV carried by mosquitoes in the local, and to detect antibody of JE in the clinical specimens, providing the guide for strategies of prevention and control against JE in Anhui province. Firstly, we analyzed the epidemiological characteristics of reported JE cases from2004to2011in Anhui province to understand its current trends and features. Secondly, three cities from north to south in Anhui province were selected to collect mosquitoes and clinical specimens of patients with fever to carry out the etiological investigation to better understand the prevalence status of JEV in the nature and in the patients with fever. The results reported in this study are as follows,1. Epidemiological analysis of JE cases from2004to2011in Anhui province1) A total of1651JE cases were reported from2004to2011in Anhui province, with annual incidence of0.3359/100,000; while the number of mortalities is50, with annual mortality rate of0.0102/100,000. The highest morbidity and mortality occurs in2006.2) A total of17cities have reported JE cases from2004to2011in Anhui province. The top4cities of JE cases reported are Fuyang, Liuan, Haozhou and Anqing, and the number of JE cases in these4cities accounts for59.1%of the total cases.3) A clear peak incidence period is from July to August each year in Anhui province.4) In Anhui province, JE cases are distributed in all age groups, but the majority is children under the age of15, accounting for95.2%of the total cases. The male patient was significantly more than females, with a ratio was1:0.52. The occupational distribution indicated that the majority of patient is diaspora children followed by student and kindergarten children.With the development of economy and society and the wide usage of JE vaccine, compared to2002and before, the morbidity and mortality of JE in recent years in Anhui province decreased substantially, however the higher prevalence level of JE existed in some areas, especially in Fuyang, Liuan, Haozhou and Anqing city. Thus, it is needed to strengthen the comprehensive measure of prevention and control against JE in the local in order to reduce the morbidity and mortality. The majority of patient is children under the age of15, particularly the diaspora children. It is necessary to strengthen the publicity, education and immunization of this population to reduce the immune blank.2. Etiological investigation of JE in Anhui province1) In the summer of2010, mosquitoes were collected in Fuyang, Huainan and Anqing city. A total of7651mosquitoes representing3species from3genera were collected in this study. The dominant mosquito species was Cx. tritaeniorhynchus.2) Mosquitoes were homogenized in155pools. After homogenized supernatants were inoculated onto monolayers of BHK-21and C6/36cells,11pools yielded11virus isolates. The supernatant of11isolates both caused cytopathic effects (CPE) in BHK-21and C6/36cells in successive cell passages.11isolates were identified as JEV by serology and molecular biology methods.3) Phylogenetic trees derived from nucleotide sequences of E gene of JEV strains indicated that11JEVs newly isolated from Anhui province were members of genotype I JEV. A more detailed analysis indicated that the Anhui JEVs are most closely related to JEV isolates from Shanghai and Zhejiang. There were14amino acid divergences in E protein when compared with vaccine strain SA14-14-2but they are not the key virulence sites.It is the first report that genotype I JEV was isolated in Anhui province and the molecular and phylogenetic characteristics of newly isolated JEVs were determined, indicating that genotype I JEV is circulating in Anhui province. Therefore, increased surveillance and more effective diagnosis of viral encephalitis caused by genotype I JEV is an issue of great concern in the local.3. Study on JEV infection among the patients with fever in Anhui province in20101) During summer to autumn in2010, a total of548clinical specimens from patients with fever were collected in local hospital of Fuyang, Huainan and Anqing city in Anhui province, of which serum specimens were514and CSF specimens were34.2)11positive specimens were detected from548specimens by using JEV IgM ELISA kit, containing5serum and6CSF. JEV antibody positive rate is2.0%.3)2JEV antibody positive specimens were detected from Anqing city. The age of patients whose JEV antibody was positive were18and63respectively.9positive specimens were detected from Huainan city. The patients whose JEV antibody were positive were children under the age of10. The onsets of11patients were during summer and autumn that is the peak incidence period of JE.In this study, JEV antibody was detected from specimens of patients with fever and viral encephalitis. Since this part of patients do not belong to the object for JE case report, suggesting that there are missed diagnosis and underreporting of JE in Anhui province to some extent. Thus, it is needed to strengthen laboratory detection and diagnosis of JE to reduce the missed diagnosis and underreporting of JE.The significance of this studyIn this study, systematic analysis of epidemiological data from2004to2011in Anhui province was carried out on seasonal distribution, geographic distribution, age distribution and occupational distribution. The characteristics and trend of JE epidemic in Anhui province was described systematically, which can help deterinine the key areas and populations for the prevention and control of JE in Anhui province. Genotype I JEVs were isolated in Anhui province for the first time and the molecular characteristic of newly isolated JEVs was determined, providing the etiological basis for the prevention and control of JE in the local. JEV antibody was detected from specimens of patients with fever and viral encephalitis, suggesting that there are missed diagnosis and underreporting of JE in Anhui province, highlighting the necessity to strengthen the laboratory detection and diagnosis of JE. The implementation of this study provides the epidemiological and etiological basis for the enactment of policies for JE prevention and control, the adjustment of the immunization program strategies, the strengthening of the JE laboratory diagnosis and the improvement of disease network reporting system in Anhui province.