Spotted Fever Group Infecting Ticks (Acari: Ixodidae), Yak (), and Tibetan Sheep () in the Qinghai-Tibetan Plateau Area, China

The Qinghai-Tibet Plateau Area (QTPA) has a complex natural ecosystem, causing a greatly increased risk of spreading various tick-borne diseases including rickettsial infections, which are regarded as one of the oldest known vector-borne zoonoses. However, the information of one of its pathogen, spotted fever group (SFG ), is limited in tick vectors and animals in this area. Therefore, this study focused on the investigation of SFG in tick vectors, yaks (), and Tibetan sheep () in the QTPA. A total of 1,000 samples were collected from nine sampling sites, including 425 of yaks, 309 of Tibetan sheep, 266 of ticks. By morphological examination, PCR, and sequencing, we confirmed the species of all collected ticks. All tick samples, all yak and Tibetan sheep blood samples were detected based on SFG and gene. The results showed that all tick samples were identified to be , and the positive rates of SFG were 5.9% (25/425), 0.3% (1/309), and 54.1% (144/266) in yaks, Tibetan sheep, and ticks, respectively. All positive samples were sequenced, and BLASTn analysis of the gene sequences of SFG showed that all positive samples from animals and ticks had 99.04-100% identity with yak and horse isolates from Qinghai Province, China. BLASTn analysis of the gene sequences of SFG showed that all positive samples had 97.60-98.72% identity with tick isolates from Ukraine. In addition, the phylogenetic analysis showed that all the SFG and sequences obtained from this study belong to the same clade as isolated from livestock and ticks from China and other countries. Molecularly, this study detected and characterized SFG both in the tick vectors and animals, suggesting that the relationship between SFG , tick species and animal hosts should be explored to understand their interrelationships, which provide a theoretical basis for preventing control of this pathogen.