Study On Density Monitoring,Virus Carrying And Insecticide Resistance Of Aedes Albopitus In Pingshan District Of Shenzhen City

OBJECTIVES:1.To assess the risk of dengue fever and provide a scientific basis for the prediction and warning of the local dengue fever by investigating vector species density and seasonal fluctuation,the type and quantity of habitats,and the dengue virus infection of dengue transmitting vector Aedes albopictus in Pingshan District of Shenzhen City.2.To evaluate the resistance degree of Aedes albopictus against three types of commonly used chemical insecticides in Pingshan District,and to preliminary explore of its metabolic resistance mechanism from the biochemical level of enzymology,so as to provide a theoretical basis for timely adjustment of resistance governance strategies.METHODS:1.Surveillance on the density of adult Aedes albopictus and larvae in different habitats were conducted by utilizing the methods of mosquito oviposition trap and Breteau index methods from 2016 to 2017.Both larvae and eggs were collected and reared to adults in our laboratory.Nucleic acid was extracted and dengue virus was identified with real-time reverse transcriptase polymerase chain reaction(RT-PCR).2.The insecticide resistance of adult mosquitoes were tested using the contact tube method recommended by WHO.The resistance levels of the Pingshan population and sensitive strain of Aedes albopictus against pyrethroids,organophosphate and carbamate insecticides were tested,and the non-specific esterase(NSE),mixed function oxidase(MFO)and glutathione S-transferase(GST)activity of two populations of adult mosquitoes were determined to understand their role in metabolic resistance.RESULTS:1.Density and habitats of the Aedes albopitus in Pingshan District: The average mosquito and oviposition positive index in 2016 and 2017 were 5.60 and 8.64,respectively.Oviposition index and mosquito and oviposition positive index between different habitats in 2017 were all highest in the residential areas and lowest in the park(P<0.05).The average breteau index in 2016 and 2017 were 5.81 and 3.40 respectively.The breteau index and house index in 2016,breteau index and container index and house index in 2017 of different habitats were significantly different,and the density index of residential areas were higher than those in external environment(P<0.05).Aedes albopictus could be discovered in Pingshan District all year round.The fluctuation trend of positive indexes were basically the same and the density of Aedes albopictus increased month by month from April,reaching the peak around August,except that the container index fluctuation curve in 2016 showed a three-peak distribution.There were more temporary breeding containers for Aedes albopictus in Pingshan,and the positive rate for temporary breeding containers was higher.Idle containers were the main types of habitats.The highest positive rate of containers was used tires,and the second highest was bamboo or tree hole or stone cave.The positive rate of twin containers were significantly different among different habitats(P<0.05).2.Dengue virus infection of Aedes albopictus in Pingshan District: From April to August in 2016,a total of 1190 mosquitoes of Aedes albopictus were detected in 53 batches,with an average of 22 and all were negative for dengue virus.3.Resistance level of Aedes albopictus in Pingshan District: The 24-hour mortality rates at diagnostic doses in Pingshan population and sensitive strain of Aedes albopictus ranged from(54.65-99.08)% and(98.48-100.00)%,respectively.Laboratory strains were sensitive to all kinds of insecticides,but the Pingshan population were tested against 0.4% beta-cypermethrin,3% permethrin and 0.1% deltamethrin for 1h and the 24 h mortality rates were 54.65%,59.22% and 65.92%,respectively,indicating resistance.When exposed to 0.5% lambda-cyhalothrin,1.4% alpha-cypermethrin,0.2% fenitrothion and 0.5% malathion for 1h,the 24 h mortality rates were 93.50%、94.85%、88.05%、95.60%,indicating suspicious resistance,but it was sensitive to 0.05% propoxur with mortality 99.08%.4.Study of metabolic resistance mechanism of Aedes albopictus: The activity of mixed function oxidase and glutathione S-transferase of Aedes albopictus in the wild were higher than that of the sensitive strain(P<0.05),and the enzyme activity ratio were 1.14 and 1.43,respectively.The activity of three metabolic enzyme showed an abnormal distribution,accounting for 31.08% of individuals with glutathione S-transferase resistance,and 14.86% of individuals with non-specific esterase and mixed function oxidase resistance.Resistance individuals with two or more simultaneous elevated enzyme activity also accounted for a certain proportion.CONCLUSIONS:1.Dengue virus in Aedes albopictus was not detected in Pingshan District,however,dengue transmitting vectors were widely distributed and the density was high.A risk of local outbreak of dengue fever can be immediate by imported cases.Surveillance,prevention and control of the key areas such as old village and closed industial park should be strengthened.2.Aedes albopictus in Pingshan District is highly resistant to pyrethroids and relatively low resistant to organophosphate insectides,but sensitive to carbamate insecticides.The increase of the activity of mixed function oxidase and glutathione S-transferase metabolic enzyme may be the reason for high resistant to pyrethroids.Periodical resistance monitoring and the research on related resistance mechanism should be strengthened to formulate timely scientific and rational resistance management program.