Impacts Of Tropical Cyclone On The Density Of Aedes Mosquitoes And The Incidence Of Dengue

BackgroundDengue is an acute infectious disease transmitted by Aedes mosquitoes,which is climatesensitive.Meteorological factors play an important role in the spread of dengue.As a result of global warming,dengue has become the most widespread and rapidly growing mosquito-borne disease,with 2.5 billion people currently at risk.Dengue outbreaks in China have spread from southeast coastal areas to inland areas.Dengue is the sensitive diseases of tropical cyclone.During tropical cyclones,regional meteorological conditions fluctuated and affected Aedes mosquito density and disease transmission.China is one of the country’s most seriously affected by tropical cyclones,and the southeast coastal areas are affected by 7-9 times on average every year.Under the trend of global warming,the intensity and frequency of tropical cyclones affecting China will increase in the future.Aedes albopictus and Aedes aegypti are the main vectors of dengue fever transmission in China,which are mainly distributed in southeast coastal China with an expanding trend.National vector Aedes surveillance sites have been established in 23 provinces,including Zhejiang Province,Fujian Province,Guangdong Province,Guangxi Zhuang Autonomous Region,Yunnan Province,and Hainan Province.These provinces are also the main dengue epidemic areas and suffer tropical cyclones.Among previous studies on the impacts of extreme weather events on the incidence of dengue,few studies have focused on the control of mosquito density.However,it is the main factor affecting the incidence of dengue.The national vector Aedes surveillance-class I area was taken as the research site to quantitatively analyze theimpact of tropical cyclones on the incidence of dengue fever and Aedes density.It was analyzed from the provincial and municipal levels respectively that the impact of tropical cyclones on the incidence of dengue.Among them,the provincial level controls the variable of Aedes mosquito density.This study explores the impact of tropical cyclones on the incidence of dengue fever and the density of Aedes mosquitoes,which is beneficial to the formation of national public health policies to cope with climate change.Objectives1.To understand the distribution of dengue in Zhejiang,Fujian,Guangdong,Guangxi,Yunnan,Hainan provinces in China from April to November during 2015 to 2019.2.To explore whether the density of mosquitoes in the provincial area changes and the lag effect when affected by the tropical cyclone.3.To evaluate the impact of tropical cyclones on the incidence of dengue,the regional differences and sources of heterogeneity in different provinces.4.To analyze the impact and lag effect of tropical cyclones on the incidence of dengue in cities with a high incidence of dengue.Methods1.Data collection:Data of reported dengue cases from April to November from 2015 to 2019 were obtained from the Chinese Center for Disease Control and Prevention through the China National Notifiable Disease Surveillance System.According to the case infected area,we divided the case into the imported and indigenous cases.Data on the density of mosquitoes were collected from the China National vector Surveillance System.Tropical cyclone data were obtained from the China Climate Bulletin and the China Meteorological Administration tropical cyclone database.Meteorological data during the same period were downloaded from the China Meteorological Data Sharing Service System.2.Statistical analysis(1)Figures and tables were used to describe the spatial,temporal,and population distribution of dengue.The spatiotemporal variation of Aedes mosquitoes during the study period was visualized.(2)Wilcox test was used to test whether the breteau index was different between the tropical cyclone affected group and the normal group in class I Aedes mosquitoes monitoring area and provinces.(3)A two-stage model was used to evaluate the relationship between tropical cyclones and dengue incidence at the area and province level.In the first stage,a generalized additive model was conducted to obtain the estimated impact of the tropical cyclone on dengue at the province level.In the second stage,multivariate meta-analysis was used to combine the cumulative exposure-response effects of different provinces to evaluate the relationship between tropical cyclones and dengue at class I Aedes mosquitoes monitoring area level.Meta-regression model was used to explore the heterogeneity sources.(4)The impact and lag effect of the tropical cyclone on dengue were analyzed by using distributed lag non-linear model with a daily unit.The above statistical analysis is based on R 4.0.3 software and ArcGIS 10.2 to draw descriptive maps.Results1.A total of 26425 indigenous dengue cases were reported in class I Aedes mosquitoes monitoring area during the study period.The incidence of dengue was seasonal and peaked from August to October every year.There was a peak of dengue in 2019,with the total number of indigenous cases four times than previous average in class Ⅰ Aedes mosquitoes monitoring area.The prevalent year of dengue was various in different provinces,and only Fujian province had dengue outbreak in 2016.The high incidence areas were mainly concentrated in provincial capitals and border cities with higher population mobility in the study area.From 2015 to 2018,the proportion of male and female was similar in indigenous cases,and cases were mainly in population aged 35-65 years,accounting for 48.2%.2.The density of Aedes mosquitoes had a seasonal pattern,reaching the peak from June to October every year.During the study period,the difference of breteau index in various provinces was statistically significant(P<0.001).Zhejiang province had the highest density of Aedes mosquitoes(BI P50=17.37),while Guangdong province had the lowest(BI P50=3.24).Tropical cyclones had an effect on the density of Aedes mosquitoes in class I Aedes mosquitoes monitoring area.The breteau index was 10.85 and 8.10 in the group affected by tropical cyclones and the normal group respectively.The effects of tropical cyclones on the density of Aedes mosquitoes varied in different provinces.The breteau index increased in Hainan province,Guangxi Province and Yunnan Province within half a month affected by tropical cyclones.After a lag of one month,Yunnan province is the only one that with higher density of Aedes mosquitoes than normal times after tropical cyclone.3.The impact of tropical cyclones on the dengue varied in different provinces.The pooled effect of class I Aedes mosquitoes monitoring area showed that the risk of dengue was reduced on lag a half month(RR=0.71,95%CI:0.52～0.97).The risk of dengue increased in Zhejiang and Guangdong during the half months affected by tropical cyclone(RR=2.06,95%CI:1.44～2.96;RR=1.04,95%CI:1.14～1.24),and the risk of disease gradually decreased after half month and one month lag.In Fujian and Hainan,the risk increased after one month lag(RR=1.42,95%CI:1.71～2.06;RR=3.95,95%CI:1.15～13.53).The sources of heterogeneity among six provinces were identified by meta-regression,which included population density,annual average number of imported cases and urban green coverage area rate.4.Tropical cyclones affected the incidence risk of dengue in Fuzhou,Guangzhou and Xishuangbanna Dai autonomous prefecture,the effect showed an approximately inverted U curve.Different tropical cyclones had various effects on the incidence of dengue in cities,and the higher the tropical cyclone grade,the higher the risk of dengue.Different cities had different days of increased dengue risk under tropical cyclone.After affected by typical typhoon,the incidence risk of dengue increased in Fuzhou at lag 9-15 days,in Guangzhou at lag 8-17 days and in Xishuangbanna Dai autonomous prefecture at lag 8-14days.The incidence risk all reached the highest after 12 days lag in three cities.(RR=1.24,95%CI:1.06-1.46;RR=1.14,95%CI:1.07～1.21;RR=1.67,95%CI:1.17～2.38).Conclusions1.Dengue tended to occur in the middle-aged population aged 35 to 65 in China,with a high incidence in late summer and early autumn every year.2.The incidence of dengue was concentrated in provincial capitals and border cities with higher population mobility in class I Aedes mosquitoes monitoring area.3.The impact of the tropical cyclone on dengue varied in different provinces.Zhejiang,Guangdong had a higher risk in the half-month when tropical cyclone occurs than normal times.The impact of tropical cyclones on the incidence of dengue in cities with a high incidence of dengue showed an obvious lag effect,and the impact effect reached the peak after lag about 2 weeks.4.During tropical cyclones,the density of Aedes mosquitoes increased in the class I Aedes mosquitoes monitoring area,especially in Hainan,Guangxi,and Yunnan.During a tropical cyclone,mosquito larva elimination should be carried out in time to reduce the density of Aedes mosquitoes,to decrease the risk of dengue among the population.