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 (