Research On The Distribution Characteristics Of Mosquitoes And Ticks And The Background Of Pathogens Carried By Them In Yadong,Tibet

Objective:(1)To investigate the characteristics of natural foci and the spatial distribution of mosquitoes and ticks in Yadong,Tibet.(2)To identify the species of ticks in Yadong by molecular biological methods and phylogenetic analysis were performed.(3)To study the infection of tick-borne pathogens among residents and ticks in Yadong.Methods:(1)Twenty sampling points were selected as study objects in Yadong natural foci in July2021 to collect and analyze geographic landscape factors and host information such as the topography,landform,climate,hydrology,vegetation,population and livestock density of Yadong natural foci,Tibet.Mosquitoes were collected by light trapping method,ticks were captured by manual inspection and flag dragging method,and the spatial distribution characteristics of mosquitoes and ticks were analyzed.(2)23 ticks collected in Yadong,Tibet in July 2021 were used to amplify the gene sequences of cytochrome oxidase subunit I(COX I),mitochondrial 16 S ribo-somal DNA(16S r DNA)and mitochondrial 12 S ribo-somal DNA(12S rDNA),and identified by molecular biology classification.(3)The gene sequences of spotted fever group rickettsia(SFGR),Borrelia burgdorferi,Francisella tularensis and Coxiella burnetii in ticks were amplified by PCR and sequenced,and phylogenetic analysis were performed;184 serum samples collected from Yadong in 2021 were used to screen the antibody of Lyme disease,Q Fever,Spotted fever and Tularaemia by ELISA,and the infection of tick-borne pathogens in Yadong was comprehensively analyzed.Results:(1)The terrain of Yadong natural foci had the character of higher in the north and lower in the south,with a drop of more than 5,000 meters between the north and the south.There are abundant water resources in Yadong natural foci,and the climate and ecological environment were characterized by vertical distribution along with altitude gradients obviously.From 2010 to 2021,an average station pressure in this area is 452.8mm Hg a year,month maximum temperature averaged 8.7℃ in July,rainfall is mostly concentrated from July to August,and July is the highest,averaged 134.5mm,month air relative humidity averaged 81.3% in July.A total of 6,897 Diptera insects belonging to 5 families were collected by light-baiting method.The dominant population was Sciaridae,accounting for 89.69% of the total number of insects.They were not blood-sucking mosquitoes after morphological identification.A total of23 ticks were caught in 2014 parasitic animals through body surface examination,of which 20 were morphologically identified as Ixodes and 3 were Haemaphysalis;Free ticks were not captured by flag dragging in 16 sampling points of Yadong natural foci,Tibet.(2)The ticks(Ixodes)collected in Yadong,Tibet,belonged to two categories,of which the COX I,16 S r DNA and 12 S r DNA gene sequences of the ticks in this study were 99.5%,97.57% and 99.12% respectively similar to those of Ixodes nuttallianus in Gen Bank;The similarity between the COX I and 16 S r DNA gene sequences of another kind of ticks(Ixodes)and the COX I and 16 S r DNA gene sequences of Ixodes ovatus in Gen Bank were 88.29% and95.75%,respectively;The similarity between the COX I,16 S r DNA and 12 S r DNA gene sequences of ticks(Haemaphysalis)and those of Haemaphysalis Tibet in Gen Bank were96.04%,96.17% and 97.47%,respectively.(3)The sequence amplification results of Borrelia burgdorferi,Francisella tularensis and Coxsiella burnetii in this study were negative,and the glt A gene amplification of spotted fever group Rickettsia was positive,The similarity between the glt A gene sequences and Candidatus Rickettsia tarasevichiae,Rickettsia raoultii,Rickettsia canadensis and Rickettsia endosymbiont of Eucalyptus brunneri in Gen Bank were 96.77%,96.76%,95.35% and95.35%,respectively.Among 184 serum samples from Yadong,the positive rates of Lyme disease,Q fever,Spotted fever and Tularaemia were 6.52%,12.50%,8.70% and 10.87%,respectively.Conclusion:(1)The climate and ecological environment of Yadong natural foci were characterized by vertical distribution along with altitude gradients obviously,and the distribution of mosquitoes and ticks had unique geographical and temporal characteristics.The highest temperature in Yadong was in July,with an average temperature of 8.7 ℃,mosquitoes and ticks are active,but the density is not high,the density of mosquitoes in Yadong showed a trend of higher in the south and lower in the north,the survey of ticks should be conducted from April to June when there was low temperature and little rain,the monitoring of local mosquitoes and ticks should be based on time and local conditions.(2)Ixodes nuttallianus,Ixodes ovatus and Haemaphysalis tibetensis may be the dominant ticks in Yadong,Tibet.The possibility of the presence of Haemaphysalis nepalensis is not ruled out,suggesting that we should be alert to the risk of introducing vector diseases in border trade and animal migration.(3)SFGR infection of Ticks in Yadong was possible.Lyme disease,Q fever,spotted fever and Tularaemia infection were prevalent in the population of Yadong.It is necessary to strengthen the prevention and control of tick-borne diseases.