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.
Highlights
Rickettsia spp. (Rickettsiales: Rickettsiaceae) are obligate intracellular bacteria that causes rickettsioses, which is one of the oldest known vector-borne zoonoses diseases [1]
In China, 11 spotted fever group (SFG) Rickettsia species have been detected in tick vectors and animals, some of which have been characterized as human pathogens [6]
The 266 tick samples were collected, some of which were engorged ticks collected on the surface of yaks and Tibetan sheep, and the rest of ticks were collected by dragging the grasslands with a flannel cloth
Summary
Rickettsia spp. (Rickettsiales: Rickettsiaceae) are obligate intracellular bacteria that causes rickettsioses, which is one of the oldest known vector-borne zoonoses diseases [1]. 26 SFG Rickettsia species had been reported, 16 of which were associated with human diseases [3, 4]. SFG Rickettsia includes more than 20 different species, including pathogenic species that cause human and animal incidence, and nonpathogenic species [5]. In China, 11 SFG Rickettsia species have been detected in tick vectors and animals, some of which have been characterized as human pathogens [6]. SFG Rickettsia was detected in a variety of ticks, including Haemaphysalis qinghaiensis in Yunnan Province and Harbin Province in China [5, 7, 8]. There are few reports of the determination of SFG Rickettsia in H. qinghaiensis in the Qinghai–Tibetan Plateau Area (QTPA) [7, 9]
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