Objective To investigate the difference in the positive rate of Orientia tsutsugamushi between different organs of small mammals, and to provide a reference for the pathogen monitoring of scrub typhus. Methods Liver, spleen, lung, kidney, and ear samples were collected from 105 small mammals collected in Yongcheng city of Henan province, China in October 2017, and liver, spleen, and ear samples were collected from 324 small mammals collected in Pinggu district of Beijing, China from September to November 2018. DNA was extracted, and nested PCR amplification was used to detect the nucleic acid fragment of the 56 kDa protein gene of O. tsutsugamushi. The specimens with specific bands were genotyped by comparison of nucleotide sequence, and the positive rate was calculated. Results The positive rate of O. tsutsugamushi in small mammals was 10.48% in Yongcheng city and 12.96% in Pinggu district, with no significant difference ( χ ²=0.494, P=0.504). The positive rate of O. tsutsugamushi in different organs within the same site was 0.98%-14.81%; pairwise comparison showed that the positive rate of O. tsutsugamushi in the ear of the small mammals in Yongcheng city was higher than that in the other four organs, and the positive rate of O. tsutsugamushi in the liver of the small animals in Pinggu district was significantly higher than that in the spleen ( χ ²=5.818, P=0.022). The comparison of the two places showed that the positive rate of O. tsutsugamushi in the ear of the small mammals in Yongcheng city was significantly higher than that in Pinggu district ( χ ²=6.525, P=0.011). For the small mammals in Pinggu district, the positive rate of Shimokoshi-type O. tsutsugamushi in the spleen was lower than that in liver and the ear, while there was no significant difference in the positive rate of Kawasaki-type O. tsutsugamushi between the different organs ( χ ²=1.560, P=0.455). The pooled analysis of the detection results of the liver and the spleen in Yongcheng city and Pinggu district showed that the positive rate of O. tsutsugamushi in the liver was higher than that in the spleen. The results of consistency test showed no significant difference (Kappa=0.015, P=0.744), with poor consistency of positive infection in the liver and the spleen. Conclusion There are no significant differences in the positive rates of Kawasaki-type O. tsutsugamushi in the liver, spleen, lung, and kidney of small mammals between Yongcheng city and Pinggu district, while the positive rate of Shimokoshi-type O. tsutsugamushi in the liver and the ear is higher than that in the spleen. Detection of O. tsutsugamushi in the organ of various small mammals or in multiple organs can improve the detection rate of O. tsutsugamushi, and rodent ears can also be used as samples for the pathogen monitoring of scrub typhus.

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.

【Abstract】 Objective To discuss the influence factors of mice?to?mice plague in Yanchi county of Ningxia. Methods The density of field mouse was investigated by stratified sampling method. The mice were dissected and the viscera were taken out to do etiology examination by pressing culture method. The fleas collected were separated randomly into groups to do bacteriological analysis. Results During 2002-2006, the monitoring areas of Meriones unguiculatus plague accounted for 15.93% of total foci areas in Yanchi county. The average density of M.unguiculatus was 11.02/ hm2, and the infection rate of flea and the flea index were 34.17% and 0.85, respectively. Three indexes mentioned above were the highest in 2005 and 2006. There were 4633 field mice captured during 5 years, which belonged to 8 species 6 genus 4 family.  Sixty eight strains of Yersinia pestis were isolated including 57 strains from 3523 mice and 11 strains from 2393 fleas (about 380 groups). Conclusion M.unguiculatus and M.meridianus are the dominant species. Dipus sagitta, D.sibirica, Cricetulus barabensis and Phoodopus roborovskii are common species, and Cricetulus migratorius and Spermophilus dauricus are the rare species. The outbreak of mice plague has the positive correlation with mice density, infection rate of flea to mice and flea index. The projects about returning farmland to forests and pastures and forbidding grazing periodically increase the outbreak frequency and risk of mice?to?mice plague in the short time in Yanchi county.