| BackgroundRickettsiosis is a generic term for a group of zoonotic diseases of natural origin caused by rickettsiae.In recent years,an increasing number of human infections caused by rickettsiae have been reported worldwide,and human infections have also emerged in China.Rickettsia is a group of microorganisms between bacteria and viruses,which are Gram-negative,specialized intracellular parasitic microorganisms,of which more than 20 species have been shown to cause diseases in humans.Rickettsia is mainly transmitted by rats and their parasitic ticks,mites,and fleas,etc.Rickettsia has been detected mainly in rats and ticks in the past.Chigger mites are also at risk of transmitting Rickettsia,but there are very few studies on chigger mites carrying Rickettsia.The well-developed animal husbandry and tourism in the eastern grasslands of Inner Mongolia provide good conditions for the transmission of natural epidemic diseases among rats and mites.ObjectivesTo understand the species composition and distribution of rats and their parasitic chigger mites in the eastern grassland of Inner Mongolia.To understand the distribution of chigger mites in different sampling sites,months and hosts and their possible influencing factors.To understand the positive rate and species of rickettsiae and Orientia tsutsugamushi in rats and their surface parasitic chigger mites.And to provide a theoretical basis for the prevention and control of local rickettsiosis.MethodsSurveys were conducted in May,July and September 2021 in eight areas of the eastern grasslands of Inner Mongolia.Two to three sample plots were selected in each sampling site,and the 5-meter wiring method was used to trap and identify the species of mites.Specimens of chigger mites were made and morphological species identification was carried out according to "Chinese Chigger Mites" and so on.PCR was used to amplify the 17 kDa,gltA and ompB genes of rickettsiae and the 56 kDa gene of Orientia tsutsugamushi in mice and chigger mites to construct a phylogenetic tree and identify pathogenic species.Maps were made using ArcGIS,data were entered in excel,and a chi-square test was used to test whether differences in the distribution of scrub mites were statistically significant.Results1.1210 complete specimens were made and identified as 2 families,3 genera and 3 species,of which 1174 were Leptotrombidium oblongatum,21 were Ascoschoengastia crassiclava,and 15 were Multisetosa ochotonae,accounting for 97.02%,1.74%and 1.24%respectively.Leptotrombidium oblongatum was the dominant species.The chigger mites were mainly distributed in East Uzhumqin Banner and Xinbahu Right Banner near the border of China,Mongolia and Russia;they were distributed in May,July and September;they have no host specificity and were mainly found in Lasiopodomys brandtii,Spermophilus dauricus,Cricetulus barabensis and Meriones unguiculatus.2.A total of 588 DNA samples were extracted,and the detection rate of rickettsia was 0.51%,which was Rickettsia sibirica.All of them were distributed in July,and their hosts were Lasiopodomys brandtii and Spermophilus dauricus;the detection rate of Orientia tsutsugamushi was 0.00%.A total of 302 chigger mites were detected,and the detection rate of both rickettsia and Orientia tsutsugamushi was 0.00%.Conclusions1.The species of chigger mites in the eastern grassland area of Inner Mongolia were relatively homogeneous,with Leptotrombidium oblongatum as the dominant mite species.They didn’t have host specificity and were distributed in May,July and September,mainly in mountainous areas and plateaus at altitudes of 1,000 to 3,000 m,and in cold climatic areas.Research on chigger mites should be strengthened to provide scientific basis for local scrub typhus prevention and control.2.Rats in the eastern grassland of Inner Mongolia carried Rickettsia sibirica,which can cause North Asian tick-borne spotted fever,mainly distributed in July.Rickettsiae detection should be strengthened to provide a theoretical basis for the prevention and control of local rickettsiosis. |
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