Abstract: Objective To investigate the species of hosts and vectors, seasonal variation, and pathogen genotypes in the natural focus of scrub typhus in Pinggu district of Beijing, China through field investigation and laboratory study, and to provide a basis for the prevention and control of scrub typhus. Methods Rat traps were placed in field every month for one year, and small mammals were captured to collect chigger mites on body surface and analyze the number, species composition, seasonal variation, and spatial distribution of chigger mites. The small mammals were dissected to collect the liver and the spleen and extract DNA from the tissue, and nested PCR amplification was used to detect the 56 kDa protein gene of Orientia tsutsugamushi (Ot). The genotype of Ot was determined by nucleic acid sequence alignment and the positive rate in small mammals was calculated. Results A total of 734 small mammals belonging to 7 species were captured from September 2018 to August 2019, among which Apodemus agrarius and Mus musculus accounted for 65.26% and 30.52%, respectively, and were the dominant species in Pinggu district. Three genotypes of Ot, i.e., Shimokoshi, Kawasaki, and Japan Gilliam, were detected in the liver and spleen of small mammals, among which Shimokoshi and Kawasaki were more common. The positive rate of Ot was 10.90% in small mammals. The positive rate of Ot was 14.86% in M. musculus and 9.30% in A. agrarius, and thus they were the main hosts in Pinggu district. A total of 31 321 chigger mites belonging to 10 species were collected on the body surface of the small mammals, and Leptotrombidium subpalpale, L. linhuaikongense, and L. scutellare accounted for 84.79%, 6.49%, and 3.63%, respectively. The seasonal variation of L. scutellare was generally consistent with that of scrub typhus cases, and thus L. scutellare might be the main vector in this epidemic focus. L. scutellare was only distributed in the mountainous area and the piedmont transitional zone of Pinggu district. Conclusion A. agrarius and M. musculus are the main hosts and L. scutellare is the main vector in the natural focus of scrub typhus in Pinggu district, and there are at least three genotypes of scrub typhus pathogens. This investigation clarifies the basic elements in the natural focus of scrub typhus in Pinggu district and provides a basis for the prevention and control of scrub typhus, but further studies are needed to investigate the vector effect of other species of chigger mites.

Key words: Scrub typhus, Host, Vector, Chigger mite, Orientia tsutsugamushi

摘要： 目的 通过现场调查和实验室研究，了解北京市平谷区恙虫病疫源地宿主和媒介生物种类、季节规律及病原基因分型，为恙虫病防控提供依据。方法 每月在野外布放鼠夹，连续1年，捕获小型兽类梳捡体表恙螨，分析小兽及体表恙螨数量、种类构成、季节消长和空间分布规律。解剖小兽，取肝、脾样本，提取组织DNA，采用巢式PCR扩增检测恙虫病东方体56 kDa基因核酸片段，通过核酸序列比对确定恙虫病东方体基因分型并计算阳性率。结果 2018年9月至2019年8月共捕获小兽7种734只，其中黑线姬鼠和小家鼠分别占65.26%和30.52%，为该地优势鼠种。小兽肝、脾检出Shimokoshi、Kawasaki和Japan Gilliam 3个恙虫病东方体基因型，以前2型为主。小兽恙虫病东方体阳性率为10.90%。小家鼠和黑线姬鼠阳性率分别为14.86%和9.30%，是该地主要宿主动物。从小兽体表捡获恙螨10种31 321只，亚须纤恙螨、临淮岗纤恙螨和小盾纤恙螨分别占84.79%、6.49%和3.63%。其中小盾纤恙螨的季节消长与病例发病季节基本一致，应为该疫源地主要传播媒介。它只分布在平谷区的山区和山前过渡地带。结论 平谷区恙虫病疫源地野外以黑线姬鼠和小家鼠为主要宿主，小盾纤恙螨可能为主要传播媒介，恙虫病东方体存在至少3个基因型。本次调查明确了平谷区恙虫病疫源地的基本要素，为恙虫病防控提供了依据，但其他种类恙螨媒介作用还需开展进一步研究。

关键词: 恙虫病, 宿主, 媒介, 恙螨, 恙虫病东方体