Molecular prevalence of spotted fever group rickettsiae in ticks from Qinghai Province, northwestern China

Tick-borne rickettsioses is one of the oldest known vector-borne diseases and has been viewed as emerging or reemerging disease in China. The causative agents have been increasingly recognized and exhibited a high degree of genetic diversity and widespread distribution. This study was conducted to determine the prevalence of spotted fever group rickettsiae in ticks from Qinghai Province, northwestern China. In total, 860 questing adult ticks representing six species were collected. The SFG rickettsiae were detected in Haemaphysalis qinghaiensis (19.6%, 79/404), Dermacentor abaensis (73.7%, 157/213), Dermacentor silvarum (50.0%, 47/94), Dermacentor nuttalli (67.4%, 97/144), and Ixodes crenulatus (100%, 3/3), with an overall infection rate of 44.5%. The infection rates of SFG rickettsiae were significantly higher in Dermacentor spp. than in Haemaphysalis spp. (p < 0.05). Sequence analyses of the gltA and ompA genes revealed that five SFG rickettsiae are present in ticks in Qinghai, including R. sibirica subspecies sibirica, R. raoultii, "Candidatus Rickettsia tibetani", and "Candidatus Rickettsia gannanii" Y27 and F107. Moreover, a potential novel Rickettsia species (Rickettsia sp. 10CYF) was identified in D. nuttalli and I. crenulatus. These findings extend our knowledge of the potential vector spectrum and distribution of rickettsiae, and provided valuable information for assessing the potential risk for public health.