| Objectives:We established a comprehensive evaluation model of dengue transmission risk based on the epidemic characteristics of dengue fever in Nanjing between 2015 – 2019,to get a better understanding of the trend,high-risk groups,high-risk areas and critical control point of dengue in Nanjing.By carrying out insecticide resistance experiments on the wild population of Aedes albopictus,we can grasp the degree of drug resistance of the dengue vector Aedes mosquitoes in Nanjing,and put forward new ideas for the scientific prevention and control of dengue fever from the molecular mechanism of mono-drug resistance and cross-resistance.Methods:1.Epidemic characteristics analysis: The information of dengue fever cases from2015 to 2019 was retrieved in the "China Disease Control and Prevention Information System" database of the Chinese Center for Disease Control and Prevention,along with the literatures on the global dengue fever epidemic.The time distribution,local distribution and population distribution of epidemic data was described for a better understanding of the domestic and foreign epidemic situation and characteristics of dengue.The relevance of the domestic and foreign epidemic was analyzed to explore the reasons for the differences in epidemic characteristics.2.Building a risk evaluation model: Based on quantitative multi-analysis,the correlation matrix was calculated with normalized case data using principal component analysis.The number of principal components was extracted through the scree plot for the calculation of component matrix.Feature vectors was calculated using the rotated load matrix established by Kaiser orthogonal rotation method.Evaluation factor weights was determined using ingredient scores calculated through principal component expression.The sequence of risk influencing factors,high-risk groups and high-risk areas were established through the comprehensive evaluation of local transmission risk.3.Drug resistance experiment and mechanism analysis: The mosquito dipping method was used to test the drug resistance of the wild population of Aedes albopictus and the regression equation of the PROBIT model was fitted by the toxicity regression spline.The median lethal concentration and the drug resistance ratio were calculated to show the severity of drug resistance of Aedes albopictus in Nanjing.Results:1.This study analyzed the information of dengue fever cases reported in Nanjing from 2015 to 2019.During the past five years,the number of dengue fever cases in Nanjing increased rapidly,with June to November being the peak period of dengue fever in the city.The pattern shows a weak peak in June and a dominant peak in September,and the main overseas importing countries are Thailand and Cambodia.2.Epidemiological characteristics analysis shows that before 2011,the number of domestic dengue fever cases was controlled below 500.In 2014,there was a large dengue fever outbreak with more than 40,000 cases.The number of cases dropped rapidly to the baseline level in 2015,and increased year by year after 2016.The dengue fever epidemic in Southeast Asia and the Western Pacific region has a greater impact on China.The rainy season from June to August in Thailand is the peak of the dengue fever epidemic,and the risks of men and women being infected are the same,with15～24 years old being the high-risk age group,having a higher fatality rate.The incidence of dengue fever in Cambodia is about 1%,and the national dengue surveillance system only targets pediatric and hospitalized cases,with the highest incidence in 8-year-old children.3.According to the sequence of the comprehensive evaluation results,the first principal component of dengue fever risk is mosquito vector,with the mosquito vector density index has higher rank.The second principal component is meteorological factors.The third principal component is susceptible population factors and the fourth principal components belong to medical factors.Mosquito vector density and emergency response are key control points for the risk evaluation of local transmission of dengue fever in Nanjing.4.The comprehensive evaluation scores of the risk model show that males are at a higher risk of being infected by dengue fever than females.Farmers and retirees are at higher risk.The northern suburbs(Luhe District,Jiangbei New Area and Pukou District)and east of the main city(Xuanwu District and Qixia District)are the high-risk areas.5.The drug resistance experiment on the wild population of Aedes albopictus in Nanjing shows that the resistance ratios against deltamethrin and temephos are 8.19 and 9.52 respectively,showing low resistance(+).The resistance ratios to permethrin and beta cypermet are 11.35 and 14.28 respectively,showing moderate resistance(++).The resistance ratio to fenobucarb is 52.68,showing high resistance(+++).The resistance to temephos of the wild population of Aedes albopictus in Xuzhou is significantly higher than that of Nanjing,with a resistance ratio of 88,while the resistance to other pesticides are lower than that of Nanjing.Conclusion:1.The number of imported cases in Nanjing increased rapidly from 2015 to 2019,which should be given great attention.The domestic and foreign epidemic rate of dengue has been accelerating during the last 30 years,and the domestic dengue cases show an increasing trend every two or three years,except for the large local outbreaks in 1992 and 2014.There is a certain correlation between domestic and foreign epidemic trends,and the overall trend shows a positive correlation.Countries need to strengthen the international joint prevention and control cooperation mechanism for dengue fever to prevent the regional epidemic of dengue fever from further expanding in the world.2.The key control point for dengue fever prevention and control in Nanjing is the mosquito vector.The training of vector control technicians should be strengthen.The standardization of dengue mosquito vector emergency treatments should be enhanced,the emergency treatment effects should be implemented,and the regional mosquito vector density should be effectively reduced,in order to cut off the transmission.Strengthening publicity and education for high-risk groups and adopting corresponding prevention and control measures for high-risk areas can improve the efficiency of dengue prevention and control and save manpower,material resources and financial resources.3.Aedes mosquitoes,as one of the dengue vectors,have developed different degrees of resistance to commonly used insecticides.In the future on-site control process,low-resistance insecticides or different insecticides should be used in turns according to the results of resistance tests,to protect sensitive genes and keep the drug resistance in a low range.This will prevent the vector Aedes mosquitoes from further increasing resistance to highly resistant insecticides,leading to failure of control.4.Molecular mechanism is now an important direction of the drug resistance research of Aedes.The research on the mechanism of single-drug resistance and crossresistance still needs to be further explored,as it can be used for drug development in the future,to explore new strategies for controlling mosquitoes. |
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