Study On The Epidemic Characteristics Of Mosquito-Borne Diseases And Their Association With Climate Factors

Background and ObjectiveMosquito-borne disease is a group of infectious diseases which disseminated bymosquitoes, including malaria, JE (Japanese encephalitis), dengue fever and filariasis.Because of the global climate warming, accelerating of urbanization, rapid developmentof tourism and trading, and the deterioration of environment, the incidence ofmosquito-borne disease rises recently and the epidemic regions expand. ZhejiangProvince belongs to middle rates of the mosquito-borne disease prevalence in China,epidemic encephalitis B, tertian malaria and malignant malaria have occurred in therecent year. Anopheles sinensis, culex pipiens pallens, culex tritaeniorhynchus Giles andAedes albopictus skuse are the main pestiferous medium.Wenzhou with mild climate and dense water, which locate in the south of ZhejiangProvince, provide a favorable geographical environment for mosquitoes breeding. Therewas an outbreak of mosquito-borne disease in 1950s. The cases of mosquito-bornedisease were the most in Zhejiang Province. Because of the economic development,majority of workers enter Wenzhou from other provinces. The imported case of denguefever appeared in 2004 and 2005 in Wenzhou. It was suggested that the risk of prevalenceof mosquito-borne disease would be increased.Epidemiological characteristic and tendency of mosquito-borne disease wasdescribed. The mosquito population density, composing, virus carrier situation andseasonal variety were investigated from 2004 to 2006. In the basic of data, therelationship among meteorological factors, mosquito density and Mosquito-borne disease were explored. The results of this study could be used for preventing and controlling theprevalence of mosquito-borne infectious disease.Methods and MaterialsInformation on the morbidity of mosquito-borne disease from 1950 to 2006 wascollected from Wenzhou center for disease prevention and control. The population datawas got from Wenzhou statistical yearbook. Mosquito category and density, seasonalvariation of mosquito were monitored according to the national biological monitoringprogram, from Apr 2004 to Nov 2006. The classification and the condition of virus ofmosquitoes which were captured by mosquito traps were identified. RT-PCR would beapplied to identify the epidemic encephalitis B virus and dengue fever virus in themosquitoes.Meanwhile, the data of monthly mean temperature, monthly maximum temperature,monthly minimum temperature, relative humidity, precipitation, rainfall days and sunlighttime form 2004 to 2006 were acquired form Wenzhou weather bureau.Pearson statistic analysis was used to explore the relationship betweenmosquito-borne disease and mosquito density, and the relationship betweenmosquito-borne disease and weather parameter. Besides, mosquito density and weatherparameter were analyzed by multi-liner regression statistic analysis.ResultsThere were 127116 cases of malaria reported in Wenzhou, with average annualincidence of 40.26 per 100,000 from 1950 to 2006. The annual incidence of malaria had afalling trend. Before 1980, there were many malaria outbreaks in Wenzhou. The annualincidence of malaria in 1980s was 10.33/100,000, changed in a small range. After 90s,the incidence of malaria was at a sporadic state.There were 17333 cases of JE happened from 1952 to 2006, with the averageannual incidence of 5.76 per 100,000. The annual incidence of JE has a falling trend yearby year. After 90s, the incidence of JE was below 1 per 100,000.Before 2004, there was no case of dengue fever reported in Wenzhou. There were 2 and 3 cases of dengue fever found respectively in 2004 and 2005, and all of them wereimported cases.There was positive correlation between mosquito-borne diseases and mosquitodensity. The incidence of JE arrived at the peak period in July and August, which wasconsistent with the results of mosquito-borne diseases surveillance (mosquito anatomytest). Most of the cases of mosquito-borne diseases were focused in the high temperatureand moist Season. There were no dengue fever and JE detected in the mosquito byRT-PCR.As viewed from epidemical analysis, the results showed that monthly meantemperature, monthly maximum temperature, monthly minimum temperature,precipitation, sunlight time, relative humidity were correlated with mosquito density.Regression equation Y=-23.671+0.190X₃+0.299X₄(X₃=monthly minimum temperature,X₄=relative humidity) was obtained by multi-liner stepwise regression analysis. MultipleCorrelation Coefficients in Regression Model was 0.843, and determination coefficientwas 0.711. The results showed that the models provided a better fit to the real data.ConclusionsBoth the incidence ofmalaria and JE decreased year by year. Before 2004, there isno dengue fever report in Wenzhou, although there are imported cases found in 2004 and2005. The results suggest that immigrates from other provinces should be observed.There is a positive correlation between mosquito density and mosquito-bornedisease. Most of the cases of mosquito-borne diseases are focused in the high temperatureand moist season, which is fit for mosquito breeding.Meteorological parameters correlating with mosquito density are monthly meantemperature, monthly maximum temperature, monthly minimum temperature, relativehumidity, precipitation, sunlight time. The monthly minimum temperature and relativehumidity have a significant statistical correlation with mosquito density. The high themonthly minimum temperature and relative humidity are, the higher mosquito density is.