Identification of Rickettsia spp. in Ticks Removed from Tick-Bitten Humans in Northwestern Spain

We conducted a tick surveillance study in northwestern Spain with the aim of identifying tick-associated Rickettsia species among ticks removed from humans and to track how tick populations and their associated pathogens have changed over the years. Five genera and eight species of ticks were collected, with Ixodes ricinus being the most frequently found. By comparing our data with previous reports, a clear geographic and seasonal expansion of tick populations and the associated Rickettsia species is observed, indicating that the spatiotemporal patterns of ticks and bacteria have changed over the years. Considering the medical relevance of tick-borne rickettsioses, evaluating the infection risk to humans in tick-infested areas, as well as detecting spreading species, is essential for establishing adequate prevention and control measures. Tick-borne rickettsioses (TBRs) are distributed worldwide and are recognized as important emerging vector-borne zoonotic diseases in Europe. The aim of this study was to identify tick-associated Rickettsia among ticks removed from humans, and to track how tick populations and their associated pathogens have changed over the years. For this purpose, we conducted a tick surveillance study in northwestern Spain between 2018 and 2022. Ticks were morphologically identified and analyzed for the presence of rickettsial pathogens through the amplification of the citrate synthase (gltA) and the outer membrane protein A (ompA) genes. PCR products were sequenced and subjected to phylogenetic analyses. We collected 7397 ticks, with Ixodes ricinus being the species most frequently isolated. Based on the PCR results, Rickettsia DNA was detected in 1177 (15.91%) ticks, and 10 members of Rickettsia were identified: R. aeschlimannii, R. conorii subsp. conorii, R. conorii subsp. raoultii, R. massiliae, R. monacensis, R. sibirica subsp. mongolitimonae, R. slovaca, R. helvetica, Candidatus R. barbariae, and Candidatus R. rioja. Some of these Rickettsia have gone previously undetected in the study region. There is clear geographic and seasonal expansion not only of tick populations, but also of the associated Rickettsia. The comparison of our data with those obtained years ago provides a clear idea of how the spatiotemporal distributions of ticks and their associated Rickettsiae have changed over the years.