Epidemiological Survey of Tick-Borne Zoonotic Pathogens in Questing Ticks from the Qinghai-Tibetan Plateau of China.

Tick-borne zoonotic pathogens, including Rickettsia, Anaplasma, Ehrlichia, and Babesia spp., pose increasing risks to human and animal health. This study investigated tick species composition and associated zoonotic pathogens across high-(1500-3000 m) and very high-altitude (>3000-5500 m) zones of the Qinghai-Tibetan Plateau area (QTPA). A total of 1025 questing ticks were collected from 11 counties and identified as Haemaphysalis qinghaiensis (n = 316), Dermacentor nuttalli (n = 685), D. silvarum (n = 20), and D. niveus (n = 4). Tick composition showed clear zonal variation. In the high-altitude zone, all four species were present, with H. qinghaiensis as the dominant species. In contrast, only Dermacentor spp. were detected in the very high-altitude zone, where D. nuttalli predominated. PCR and sequence analyses detected DNA of multiple pathogens in 137/1025 (13.4%) ticks. Rickettsia was most prevalent (11.4%), followed by Anaplasmataceae (2.2%) and Babesia (0.2%). In the high-altitude zone, H. qinghaiensis harbored R. raoultii, R. slovaca, Anaplasma phagocytophilum, A. bovis, uncultured Rickettsia, Anaplasma, and Ehrlichia spp., and a Babesia motasi-like organism. In contrast, in the very high-altitude zone, D. nuttalli mainly carried R. raoultii, R. slovaca, A. phagocytophilum, A. ovis, and uncultured Rickettsia and Ehrlichia spp. In conclusion, tick species composition and associated pathogens varied between the altitude zones in QTPA. In particular, the predominance of human-biting D. nuttalli in the very high-altitude zone, together with detection of zoonotic agents, highlights the public health relevance of tick-borne infections in this region. Additional studies are essential to establish vector competence or transmission.