Objective:To learn about the characteristics of natural foci and the spatial distribution of mosquitoes and ticks in Yadong County, Tibet Autonomous Region (Tibet for short).Methods:The eco-geographical characteristics, demographic information, agricultural and animal husbandry data of the natural foci in Yadong County, Tibet were collected from the Yadong County 2020 statistical yearbook, vector data were collected from the Yadong County Center for Disease Control and Prevention, and the data of the meteorological station in Yadong County from 2010 to 2021 were collected from the World Weather Network. In July 2021, a total of 20 mosquito and tick sampling points were selected for field investigation according to the distribution characteristics of vegetation and animal husbandry of Yadong County. The light trap method was used to trap mosquitoes, and the manual inspection and flag dragging method were used to catch ticks. The spatial distribution characteristics of mosquitoes and ticks were analyzed.Results:The natural epidemic foci in Yadong County, Tibet, were high in the north and low in the south, with an elevation difference of about 5 000 m. It was rich in water resources, and the average runoff of Yadong River was 20.1 m 3/s. The climate in the north was cold and dry, and the south was mild and humid. From 2010 to 2021, the annual average station air pressure in Yadong County was 452.8 mmHg (1 mmHg = 0.133 kPa), the maximum monthly average temperature, precipitation and relative humidity of air were 8.7 ℃, 134.5 mm and 81.3%, respectively, all in July. A total of 6 897 diptera insects were attracted by the light trap method, all of which were non-blood-sucking mosquitoes. The total density was 163.77 pieces/(lamp·h), the dominant population was Muscaridae, accounting for 89.69% (6 186/6 897). In different sampling areas, Xiayadong Township collected the most mosquitoes, accounting for 67.17% (4 633/6 897); the others were Yadong County and Shangyadong Township, accounting for 27.36% (1 887/6 897) and 5.47% (377/6 897), respectively. A total 2 014 host animals were examined, and 23 parasitic ticks were caught, of which 20 were of the genus Ixodes and 3 were of the genus Haemophilus. No free ticks were caught in all ticks sampling points. Conclusions:The climate and ecological environment of the natural foci in Yadong County, Tibet have obvious vertical gradient. Mosquitoes and ticks are active, but the density is not high, the density of mosquitoes is generally high in the south and low in the north.

This study was aimed at identifying species of ticks and investigating infections with tick-borne pathogens a-mong people in Yadong,Tibet.The total of 23 ticks(Ixodes and Haemaphysalis)collected from livestock in Yadong,Tibet in July 2021,the gene sequences of cytochrome oxidase subunitⅠ(COX Ⅰ),mitochondrial 16S ribosomal DNA(16S rDNA)and mitochondrial 12S ribosomal DNA(12S rDNA)were identi-fied on the basis of molecular biology classification.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 ana-lyses were performed.In addition,184 serum samples collected from Yadong in 2021 were screened for antibodies to Lyme dis-ease,Q fever,spotted fever,and tularemia by ELISA,and infections with tick-borne pathogens in Yadong were comprehen-sively analyzed.The ticks(Ixodes)collected in Yadong,Tibet,were grouped into two categories.The COX Ⅰ,16S rDNA,and 12S rDNA gene sequences of the ticks had 99.5％,97.57％,and 99.12％ similarity,respectively,to those of Ixodes nuttallia-nus in GenBank.The similarities between the COX Ⅰ and 16S rDNA gene sequences of another Ixodes tick species and the COXⅠ and 16S rDNA gene sequences of Ixodes ovatus in GenBank were 88.29％ and 95.75％,respectively.The similarity between the COX Ⅰ,16S rDNA,and 12S rDNA gene sequences of Haemaphysalis ticks and those of Haemaphysalis Tibet in GenBank were 96.04％,96.17％,and 97.47％,respectively.The sequence amplification results for Borrelia burgdorferi,Francisella tularensis,and Coxsiella burnetii in 23 ticks were negative,whereas gltA gene amplification of spotted fever group Rickettsia in 23 ticks was positive.The similarity of gltA gene sequences with respect to those of Candidatus Rickettsia tarasevichiae,Rickettsia raoultii,Rickettsia canadensis,and a Rickettsia endosymbiont of Eucalyptus brunneri in GenBank was 96.77％,96.76％,95.35％,and 95.35％,respectively.Among 184 serum samples from Yadong,the positivity rates of Lyme disease,Q fever,spotted fever,and tularemia were 6.52％,12.50％,8.70％,and 10.87％,respectively.These results indicated that the 23 parasitic ticks collected in Yadong,Tibet,in July 2021 were Ixodes nuttallianus,Ixodes ovatus and Haemaphysalis ti-betensis,and 23 ticks were infected with SFGR.Lyme disease,Q fever,spotted fever,and tularemia infection were prevalent in the population of Yadong.Therefore,efforts to control tick-borne diseases must be strengthened.