[Prevalence of spotted fever group rickettsiae infections in ticks and among high-risk populations in the southern margin of the Gurbantunggut Desert in Xinjiang Uygur Autonomous Region].

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 antiR. 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.