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

Abstract

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 Rickettsia (SFG Rickettsia), is limited in tick vectors and animals in this area. Therefore, this study focused on the investigation of SFG Rickettsia in tick vectors, yaks (Bos grunniens), and Tibetan sheep (Ovis aries) 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 Rickettsia ompA and sca4 gene. The results showed that all tick samples were identified to be Haemaphysalis qinghaiensis, and the positive rates of SFG Rickettsia 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 ompA gene sequences of SFG Rickettsia 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 sca4 gene sequences of SFG Rickettsia 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 Rickettsia ompA and sca4 sequences obtained from this study belong to the same clade as Rickettsia raoultii isolated from livestock and ticks from China and other countries. Molecularly, this study detected and characterized SFG Rickettsia both in the tick vectors and animals, suggesting that the relationship between SFG Rickettsia, tick species and animal hosts should be explored to understand their interrelationships, which provide a theoretical basis for preventing control of this pathogen.

Keywords: Haemaphysalis qinghaiensis; Qinghai-Tibetan Plateau Area; Spotted Fever Group Rickettsia; Tibetan sheep; yak.

Figure 1

Map of the Qinghai–Tibetan Plateau Area and Qinghai Province showing the sampling sites. The green hollow circle indicates the location of the sample collection in this study.

Figure 2

The dorsal view and ventral view of Haemaphysalis qinghaiensis.

Figure 3

Phylogenetic tree based on the mitochondrial 16S rRNA gene (460 bp) of Haemaphysalis spp. obtained in this study. Bootstraps analysis was performed with 500 replicates. The solid square indicates sequence from this study. One sequence from this study is bolded. Ixodes persulcatus (JF934742) was used as outgroup.

Figure 4

Phylogenetic tree based on ompA particle sequences (209/212 bp) of spotted fever group (SFG) Rickettisa obtained in this study. Bootstraps analysis was performed with 500 replicates. The solid circle indicates sequences from Tibetan sheep, the empty circle indicates sequences from yaks, and the solid triangle indicate sequences from Haemaphysalis qinghaiensis. All sequences from this study are bolded.

Figure 5

Phylogenetic tree based on sca4 particle sequences (624 bp) of spotted fever group (SFG) Rickettsia obtained in this study. Bootstraps analysis was performed with 500 replicates. The solid triangle indicates sequences from Haemaphysalis qinghaiensis. All sequences from this study are bolded.