Genetic variability of Rickettsia spp. in Dermacentor and Haemaphysalis ticks from the Russian Far East

The Russian Far East is an endemic region for tick-borne rickettsioses. However, the prevalence and genetic variability of Rickettsia species in this region have not been extensively investigated. In this study, 188 Dermacentor silvarum, 439 Haemaphysalis concinna, and 374 Haemaphysalis japonica adult ticks were collected from four locations in Khabarovsk Province and three locations in Amur Province in the Russian Far East. These ticks were examined for the presence of Rickettsia spp. by amplifying a fragment of the gltA gene. Identified rickettsiae were genotyped by sequencing of the gltA, 16S rRNA, ompA, ompB, and sca4 genes. In the examined ticks, Rickettsia heilongjiangensis, the causative agent of Far-Eastern tick-borne rickettsiosis, was found in 10.5% of H. concinna and in 1.9% of H. japonica ticks, while Rickettsia sibirica, the agent of Siberian tick typhus, was detected in only one H. concinna tick. In addition, Rickettsia raoultii was found predominantly in D. silvarum ( > 70%) and significantly less frequently in Haemaphysalis ticks ( < 3%). Candidatus Rickettsia tarasevichiae was found in all examined tick species (1.6-5.3% in different species). Notably, this study is the first observation of Candidatus R. tarasevichiae in D. silvarum ticks. Moreover, DNA of Rickettsia canadensis was found for the first time in a H. japonica tick; DNA of Rickettsia aeschlimannii was revealed for the first time in H. concinna and H. japonica ticks. Candidatus Rickettsia principis and Candidatus Rickettsia rara were found in Haemaphysalis spp. ticks. Candidatus R. principis was associated with H. japonica and identified in 5.6% of the examined ticks, while Candidatus R. rara was found more frequently in H. concinna (3.0%) compared to H. japonica ticks (1.1%). In this study, Candidatus R. principis and Candidatus R. rara were characterized for the first time by the 16S rRNA, ompA, ompB, and sca4 genes.