Study On The Natural Foci Of Scrub Typhus In Pinggu Distinct,Beijing

Objective To analyze the epidemiological characteristics of patients of scrub typhus in Pinggu district,Beijing from 2008 to 2018.To investigate the main vectors,reservoir hosts and pathogen types of scrub typhus in Pinggu to understand the main nature and characteristics of its foci,so as to provide a theoretical basis for the prevention and control measures of scrub typhus in China.Methods1.Collecting the cases of scrub typhus report data of Pinggu district,Beijing from Chinese Center for Disease Control and Prevention "report disease monitoring information management system" from 2008 to 2018.Arc GIS was used to correlate with the county-level vector map of the country.Descriptive epidemiological analysis methods were used to analyze the population distribution characteristics of scrub typhus patients in Pinggu district,including occupation,sex,age composition ratio,regional distribution and time distribution characteristics.2.Select typical sample sites in the wild in Pinggu and samples were taken once a month from September 2018 to mid-August 2019.Mouse traps were placed by night trapping method and rat spleen and ears were collected.The rat species and mite species were identified according to the morphological characteristics of the mouse body and chigger mites.Using kit extract mice spleen genomic DNA.The nested PCR amplification was carried out by using 2 pairs of primers for detecting Ot 56 KDa coding gene in "Technical Guidelines for Prevention and Control of Scrub Typhus(Trial)" issued by the Chinese Center for Disease Control and Prevention(CDC)(No.1 [2009]),and the positive PCR products were sent to biological company for sequencing.The positive sequences were aligned with the sequence of Gen Bank’s known type,and an evolutionary tree is established with the known genotype sequence to determine the molecular typing.3.Analyze the distribution characteristics of mice and mites,and the possible host animals and vector chigger mites of scrub typhus in the field in Pinggu based on the human case data and pathogen detection data,and put forward prevention and control suggestions accordingly.Results1.From 2008 to 2018,there were 899 reported cases of scrub typhus living locally in Pinggu district,with an average annual incidence of 18.70/100,000.The incidence was on the rise before 2015,then began to decline.The incidence of scrub typhus in Pinggu is mainly from September to November each year,accounting for 99.33% of the total cases,and the peak of the disease is in October,accounting for 81.09%.It belongs to autumn epidemic area.The ratio of male to female cases was 1:1.05(438/461).The morbidity age ranged from 11 to 89 years old,with an average age of 55.91 years old,mainly in the age group of 50 to 65 years old,accounting for 52.73% of the total cases.Farmers had the highest incidence rate of occupation,accounting for 77.20% of the total cases,followed by household chores and unemployed people.The incidence area is mainly distributed in villages and towns,and the number of cases in villages and towns is 10.68 times that in urban areas.2.A total of 7,926 rat traps were recovered in this survey,and 734 small animals of 7species were captured,with a rat density of 9.26%.Apodemus agrarius and Mus musculus accounted for 65.35% and 30.43% of the total number of rats respectively,which were the dominant species in Pinggu.In different habitats,the density of mice was highest in hilly areas(11.23%)and lowest in mountainous areas(3.90%).In all habitats,the highest composition ratio was that of A.agrarius.Rats density are different in different months from September 2018 to August 2019,and the overall distribution is bimodal,with peaks occurring in June-August and November.3.A total of 31321 chigger mites were collected from 440 different mice in this survey,with a chigger mite rate of 59.95% and a mite index of 42.67.The mite index and the rate of chigger mites were higher in A.agrarius and M.musculus,and they were the dominant species of local mice,so they were the main parasitic host of local chigger mites.Tscherskia triton’s mite index was the highest,it was 168.88.A.draco has the highest rate of chigger mite,it was 100.00%.1,708 chigger mites were randomly selected to make slide specimens,which were identified as 10 species in 2 families and 5 genera.Among them,Leptotrombidium subpalpale was the dominant mite species in this region,with the mite index of 36.17,followed by L.linhuaikangense and L.scutellare.The mite index of L.subpalpale was the highest in mountain and plain and hill area.The mite index of A.agrarius and M.musculus was the highest in L.subpalpale.The peak of the total chigger mite rate and chigger mite index were in March and November.In addition,the mite index was distributed in July,August and September.The mite index of L.subpalpale was distributed except in July,August and September.L.scutellare was only detected in September to November,which was consistent with the seasonal characteristics of cases.4.In this investigation,a total of 718 rat spleens were collected,and 13 Ot positive samples were obtained by nested PCR,with a positive rate of 1.81%.The positive results were only found in the A.agrarius and M.musculus.13 Ot positive specimens were distributed in April,September,October and November in plain and hilly habitats.DNA sequence analysis showed that the positive sequences had higher homology with the DNA base sequences of JG-v type,Kawasaki type and Shimokoshi type.Conclusion1.From 2008 to 2018,the epidemic situation of scrub typhus in Pinggu district showed an overall trend of rise and then decline.The cases were concentrated in September to November of each year,belonging to the autumn epidemic area.Both men and women have the disease,the case of occupation mainly farmers;The incidence rate of township was significantly higher than that of urban area.2.A.agrarius and M.musculus in Pinggu district were the main reservoir for dominant species and scrub typhus in the wild.L.subpalpale and L.scutellare are suspected vectors.3.The molecular types of Ot in the Pinggu district were Kawasaki,Shimokoshi and JG-v.