Genetic Diversity of Rickettsiae in Dermacentor spp. Ticks on the Territory of Western Siberia and Northern Kazakhstan

The aim of this research is to study the distribution, species diversity, and genetic variability of rickettsiae in Dermacentor spp. ticks from Western Siberia and Northern Kazakhstan. Thus, samples from 571 Dermacentor ticks (406 individuals of Dermacentor reticulatus, 136 Dermacentor nuttalli, 21 Dermacentor marginatus, and 8 Dermacentor silvarum) have been examined for the presence of Rickettsia spp. DNA using nested PCR. The rickettsial species have been determined by species-specific PCR and/or sequencing of gltA gene fragments. For a number of R. raoultii samples, the sequences of the ompA (3266 bp) and ompB (4852 bp) gene fragments have been additionally determined. The examined ticks carry DNA of four Rickettsia species and a new genotype Rickettsia spp. Kos-97-Dr, which cannot be assigned to any known species. All tick species are most commonly infected with R. raoultii; the infection rate varies from 47.0 to 86.8%. Rickettsia sibirica DNA has been found in 16.1–45.7% of D. nuttalli from three sites in the Republic of Altai. DNAs of Rickettsia aeschlimannii, Rickettsia aeschlimannii-like, “Candidatus Rickettsia tarasevichiae,” and a new genotype Rickettsia sp. Kos-97-Dr have been found sporadically in D. reticulatus and D. marginatus. Based on analysis of the gltA gene fragment, seven haplotypes of R. raoultii have been identified; four of them correspond to previously described genotypes. The analysis of long fragments of the ompA and ompB genes of R. raoultii samples revealed the presence of three genetic groups corresponding to different genotypes for the gltA gene. Thus, Dermacentor spp. carry both typical and atypical species of Rickettsia spp. The existence of natural foci of Siberian tick typhus in the Republic of Altai has been demonstrated. Based on the analysis of the variable surface protein genes and conserved gltA gene, the existence of three genetic groups of R. raoultii has been shown.