Molecular Detection and Distribution of Rickettsia in Ticks Across the Country of Georgia

Abstract

Rickettsia spp. are obligate intracellular bacteria transmitted by arthropod vectors and are responsible for a range of potentially severe human infections. In Georgia, information on the geographic distribution and species diversity of Rickettsia spp. in ticks remains limited. This study investigated the prevalence and species distribution of Rickettsia spp. in ticks collected from four Georgian regions. Between May 2020 and June 2022, 4542 ticks were collected from domestic animals and the environment in Kakheti, Mtskheta-Mtianeti, Samegrelo, and Shida Kartli. Ticks were grouped into 699 pools according to species, sex, collection method, and location, then analysed using genus- and species-specific quantitative PCR assays targeting the 17 kDa antigen gene. Rickettsial DNA was detected in 158 of 699 pools, corresponding to an overall minimum infection rate (MIR) of 3.48%. The highest MIR was observed in Shida Kartli (5.13%). Six clinically relevant Rickettsia species were targeted using species-specific PCR assays; among these, Rickettsia raoultii, R. slovaca, R. aeschlimannii, and R. monacensis were detected in the examined tick samples, whereas R. massiliae and R. conorii were not detected. Mixed infections were detected in 16 pools. Dermacentor marginatus and Hyalomma marginatum were the tick species most frequently associated with Rickettsia detection, particularly in Kakheti and Shida Kartli, where species diversity was highest. These findings highlight regional variation in Rickettsia prevalence and diversity and support the need for continued tick-borne disease surveillance in Georgia.