关键词: 蜱, 斑点热群立克次体, 高危人群, 流行病学, 种系进化, 古尔班通古特沙漠, 新疆维吾尔自治区

Abstract: Objective　To investigate the prevalence of spotted fever group rickettsiae (SFGR) infections in free⁃living ticks and among high⁃risk populations in the southern margin of the Gurbantunggut Desert, Xinjiang Uygur Autonomous Region, so as to provide insights into tick⁃borne diseases prevention and control in this region. Methods　Free⁃living ticks were collected from five counties (cities) in the southern margin of the Gurbantunggut Desert, Xinjiang Uygur Autonomous Region. Tick species were identified by morphology combined with mitochondrial cytochrome c oxidase subunit Ⅰ (COI) gene analysis. Four target gene fragments of Rickettsia were amplified using a nested PCR assay, including outer membrane protein B (ompB), 17⁃kDa common surface antigen protein (17kDa), surface cell antigen 1 (sca1), and surface cell antigen 4 (sca4) genes, to detect the prevalence of SFGR infections in tick samples. Positive PCR amplification products were purified, sequenced, and subjected to sequence alignment, and phylogenetic trees were created using the neighbor⁃joining (NJ) method. Serum samples were collected from individuals at a high risk of tick exposure from six counties (cities, districts) in the southern margin of the Gurbantunggut Desert, Xinjiang Uygur Autonomous Region, and serum levels of anti⁃R. sibirica IgG antibodies were detected among these individuals using indirect immunofluorescence assay (IFA) and statistically analyzed. Results　A total of 287 free⁃living ticks were collected, and all were identified as Hyalomma asiaticum. The overall prevalence of SFGR infection was 78.40% (225/287) in tick samples, and five Rickettsia species were characterized, including R. sibirica, which shared 99.81% (515/516) sequence homology with the strain detected in Dermacentor sinicus from China; R. massiliae, which shared 99.80% (509/510) sequence homology with the strain detected in Rhipicephalus sanguineus from Ethiopia; R. raoultii, which shared 100.00% (516/516) sequence homology with the strain detected in Hyalomma asiaticum from Xinjiang Uygur Autonomous Region in China; R. africae, which shared 100.00% (524/524) sequence homology with the strain detected in Amblyomma splendidum from Ethiopia; and Candidatus Rickettsia barbariae, which shared 99.80% (499/500) sequence homology with the strain detected in steppe polecats from Xinjiang Uygur Autonomous Region in China, with R. sibirica (33.80% detection rate, 97/287) and R. raoultii (33.10%, 95/287) as dominant species. A total of 1 489 serum samples were collected from individuals at a high risk of tick exposure, and the seroprevalence of anti⁃R. sibirica IgG antibodies was 30.83% (459/1 489). There were no significant differences in the seroprevalence in terms of genders ([χ2] = 2.23, P > 0.05) or age groups ([χ2] = 6.45, P > 0.05); however, there was a region⁃specific seroprevalence rate of anti⁃R. sibirica IgG antibodies ([χ2] = 16.05, P < 0.05). Pairwise comparisons showed lower seroprevalence rate of anti⁃R. sibirica IgG antibodies among high⁃risk individuals in Midong District of Urumqi City (22.27%, 53/238) than in Wujiaqu City (34.70%, 93/268) and Manas County(37.55%, 98/261) (both P values < 0.05); however, they were not significantly different from those in the other regions (all P values > 0.05). Conclusions　Multiple SFGR species are detected in H. asiaticum ticks sampled from the southern margin of the Gurbantunggut Desert, Xinjiang Uygur Autonomous Region, where there is a potential risk of local transmission of spotted fever rickettsiosis.

Key words: Tick, Spotted fever group rickettsiae, High?risk population, Epidemiology, Phylogenetic evolution, Gurbantunggut Desert, Xinjiang Uygur Autonomous Region