High prevalence of Rickettsia spp. among moderately dense population of Dermacentor reticulatus ticks in South-central Poland.

Dermacentor reticulatus ticks play a crucial role in the circulation and maintenance of tick-borne pathogens (TBPs) foci in the environment. From a medical perspective, this species is particularly significant in transmitting TBPs classified within the spotted fever group rickettsiae (SFGR), primarily Rickettsia slovaca and R. raoultii. Moreover, in recent years, notable changes in the distribution of the species have been observed across various countries, including Poland. We hypothesized that south-central Poland, particularly the Świętokrzyskie Voivodeship, represents the current southern boundary of the continuous range of D. reticulatus ticks in the country. Our aim was to assess the population density and the prevalence of Rickettsia spp. in ticks collected from the studied area. For this purpose, 34 research sites were designated for field surveys. In total, 910 adult D. reticulatus ticks were collected and identified. Molecular analysis for the detection of Rickettsia spp. was conducted on a randomly selected subset of individual ticks. Selected PCR-positive samples underwent phylogenetic analysis. Using a random forest model, we explored the relative importance of environmental factors driving tick density. The model revealed that altitude, followed by humidity, were the primary determinants of tick density, while temperature and seasonality had negligible impacts. The mean density of D. reticulatus within its contiguous range was 3.3 ± 5.0 specimens per 100 m² (0.00-16.7/100 m²). Surveyed tick populations showed a high prevalence of Rickettsia spp. (24.00%-74.19%). Sequencing of the gltA gene in the selected PCR-positive samples confirmed that the analyzed strains belonged to the SFGR. In conclusion, our findings suggest that south-central Poland currently forms the boundary of the contiguous range of the D. reticulatus population, which is characterized by moderate density and a high prevalence of Rickettsia spp. This study underscores the influence of ecological factors on tick distribution and highlights the need for continued surveillance of this medically significant vector and its associated pathogens.