Study On The Geographical Distribution Of The Genus Of Culex And The Culex-borne Diseases In China

Background Culex is generally considered as the principal genus of mosquitoes in China.There are 76 species recorded in Fauna Sinica,some of which,including Culex tritaeniorhynchus,Culex pipiens pallens and Culex pipiens quinquefasciatus are geographically widespread.Owing to the vast territory,the meteorological environments in our country mainly include temperate,subtropical,tropical monsoon climate,temperate continental climate and highland mountain climate with the Palearctic and Oriental fauna,consequently contributing to the complicated and varied environmental factors and the breed of different species of Culex.Culex,characterized by carrying a variety of pathogens and thus being the potential or direct disease vectors,has long been of a concern to researchers.Culex tritaeniorhynchus is the main vector of Japanese encephalitis(JE)in China.However,according to past researches,records of the distribution of Culex were often confined to a province,a city or an ecological environment,which made difficult realization of long-time and comprehensive surveillance of each type of Culex that would take huge manpower and material resources.Meanwhile,the unavailability of accurate data about the distribution of Culex in unstudied regions and many differences in the identification of mosquito species and names in the process of long-term investigations,identification and analyses of Culex are likely to cause problems to the follow-up researchers.Researches regarding distribution of geographical space of Culex-related diseases in our country may well be impeded for lack of detailed statistics unless appropriate mathematical models are set to predict the risk of Culex distribution across the country,based on systematically collecting and organizing existing data,which can be of paramount importance in regard of the Culex and its associated diseases.Objective To generalize and arrange the data of the Culex species and geographic distribution in our country with records of detecting pathogens as well as to map the geographical distribution,to predict the risk of dominant Culex distribution and to provide data for the spatial distribution and related diseases of Culex.To study the effect of Culex tritaeniorhynchus during the epidemic trend of Japanese encephalitis.To explore the epidemiologic trend,characteristics and regional difference of deciding factors of JE.To provide references to Culex-related diseases and,by extension,mosquito-borne diseases.Methods Based on former literatures and historic research data,we collected Culex species in our country,listed the distribution of the dominate in tables and established the distribution map.On account of meteorological,land-use,and human-and-animal factors that may potentially affect the distribution of Culex and using Maximum Entropy method,ecological niche model was established to predict the risk of dominant Culex distribution and conduct risk assessment of the distribution area.Meanwhile,we analysed JE-endemic areas from 2012 to 2015 by the method of spatial-time scan statistic.In addition,Spearman correlation analyses were used to compare the characteristics and incidence of JE in JE-endemic areas in relation to urban or rural areas at the town level.Time-series Posssion regressional analysis model was applied to explore regional differences of the contributing factors to JE-endemic provinces at the county level.Results(1)A total of 87 Culex species in our country with numbers of each type were listed at the county level,64 species of which were mapped in the distribution at the county level;Epidemiological analysis of environmental factors was made from distribution regions of dominate Culex.A total of 19 pathogens carried in Culex in our country,including 18 viruses in 5 families and a parasitic disease were collected;The relations between 12 Culex species and its corresponding pathogens were demonstrated in the matrix plot.(2)The distribution risks of Cx.tritaeniorhynchus,Cx.pipiens pallens,Cx.pipiens quinquefasciatus,Cx.bitaeniorhynchus,Cx.modestus and Cx.pseudovishnui were predicted with the distribution maps drawn.The main factors that affected the distribution of Cx.tritaeniorhynchus were density of population and distribution of pigs,with its high distribution risk area about 3,179,000 square kilometers,involving about 12.4 billion people.The main factors that affected the distribution of Cx.pipiens pallens were the density of population and rural land,with its high distribution risk area about 1,854,000 square kilometers,involving about 10.6 billion people.The main factors that affected the distribution of Cx.pipiens quinquefasciatus were the lowest temperatures in the coldest months and the average temperatures in the driest seasons,with its high distribution risk area about 1,806,000 square kilometers,involving about 0.67 billion people.The main factors that affected the distribution of Culex modestus were the positive changes in temperatures and urban construction lands,with its high distribution risk area about 347,000 square kilometers,involving about 0.25 billion people.The main factors that affected the distribution of Culex pseudovishnui were the lowest temperatures in the coldest months and the annual average temperatures,with its high distribution risk area about 2,158,000 square kilometers,involving about 0.72 billion people.(3)There were four JE-epidemic spatiotemporal clusters from 2012 to 2015.The first was located in Southwest China,with a time frame of 2012,a center position in(27.05,106.11),a relative risk(RR)of 6.95,the ratio of rural cases to urban cases of 7.46,male cases to female cases of 1.42 and patients mainly aging between 0 to 9 years old.The JE incidence of urban and rural areas was significantly associated with the monthly mean temperature,cumulative rainfall and sunshine hours(P<0.01),with each correlation coefficient of 0.769?0.691?0.461 and 0.790?0.759?0.359,respectively.The second cluster was located in North China,with a time frame of 2013,a center position in(37.67,116.2),a relative risk(RR)of 7.70,the ratio of rural cases to urban cases of 3.4,male cases to female cases of 1.05 and patients mainly aging more than 50 years old.The JE incidence of urban and rural areas was significantly associated with the monthly mean temperature,cumulative rainfall and mean relative humidity(P<0.01),with each correlation coefficient of 0.544?0.510?0.482 and 0.706?0.381?0.437,respectively.The third cluster was located in central China,with a time frame of 2012,a center position in(32.71,113.96),a relative risk(RR)of 3.91,the ratio of rural cases to urban cases of 9.9,male cases to female cases of 1.73 and patients mainly aging between 0 to 9 years old.The JE incidence of rural areas was significantly associated with the mouthly mean temperature,cumulative rainfall,cumulative sunshine hours and relative humidity(P<0.01),with each correlation coefficient of 0.590?0.759?0.444?0.446 respectively.The JE incidence of rural areas was significantly associated with the monthly mean temperature,cumulative rainfall and sunshine hours(P<0.01),with each correlation coefficient of 0.57?0.46?0.37,respectively.The fourth cluster was located in southeastern coastal areas,with a time frame of 2013,a center position in(27.92,120.79),a relative risk(RR)of 6.83.(4)The results of regional differences among factors affecting the outbreak of JE showed that: The factors that affected the epidemiological characteristics of JE in different regions manifested their own characteristics: there was a close correlation between the distribution of pigs,Culex pipiens quinquefasciatus and the severity of JE nationally with varied factors leading to the difference in regional JE epidemic.The risk factors in 6 provinces/autonomous regions(Sichuan,Chongqing,Guizhou Yunnan,Anhui and Zhejiang)were the mean temperatures for the months and next months.The next monthly mean relative humidity correlated significantly with southwest regions and Zhejiang provinces,whereas the mean relative humidity lagging two months and for the month seemed to play a key role in Hebei,Shandong provinces and Henan,Anhui provinces,respectively,with accumulated sunshine hours for the month contributing to JE epidemic in Henan,Anhui and Zhejiang provinces.In addition,the differences between the regional distribution of pigs and Cx.pipiens quinquefasciatus directly were made manifest in the discrepancy of JE epidemic in 4 provinces/autonomous regions(Hebei,Beijing,Tianjin,Shandong)compared to their primary protective measures of the average wind speed for the month and lagging a month and secondary protective measures of local economic levels.Conclusion Geographically ubiquitous and characteristic,87 specises of Culex exist in our country,among which Cx.tritaeniorhynchus,Cx.pipiens pallens,Cx.Pipiens quinquefasciatus,Cx.bitaeniorhynchus,Cx.modestus,Cx.pseudovishnuiare are the most widely-distributed and life-thretening.The results of ecological niche models of these six culex mosquitos are ideal.A total 18 kinds of virus and a kind of parasite were detected in 12 specises of culex mosquitos.According to local distribution risk of Culex,it is imperative to take targeted measures.Take southwest and central China for instance.Preventive work should be primarily centered on children and students,while,in north China,the work of JE vaccination on farmers.On account of the leading JE-epidemic factors: Cx.tritaeniorhynchus and pigs,what we need to improve is strengthening the supervision of pig breeding and anti-mosquito as well as disease-prevention work,promoting the vaccination work of JE in depth under the scale of nation,and preparing the JE prevention in advance under the scale of district based on local risk factors and meteorological environment.