Role of ixodid ticks in circulation of Rickettsia conorii and other spotted fever group rickettsiae on the Crimean Peninsula

BACKGROUND: In total, 30 ixodid tick species were found on the Crimean Peninsula. Their epidemiological importance was directly correlated with the pathogenicity of the infectious agents that they may transmit. One such established etiological agent is Rickettsia conorii, a representative of the spotted fever group rickettsiae. Rhipicephalus sanguineus ticks serve as both a vector and reservoir for R. conorii. Studying the prevalence of pathogenic agents among the ixodid ticks is particularly crucial given Crimea’s status as a health resort and a center for resort-based medicine.

AIM: This work aimed to assess the role of ixodid ticks in the circulation of R. conorii and other spotted fever group rickettsiae.

METHODS: The ticks were collected from the vegetation, from April to September, for >7 years (2016–2022). For this, flagging and dragging methods, as well as the examination and combing of large and small livestock, horses, dogs, cats, and hedgehogs, were employed. During the outbreaks of Mediterranean spotted fever, ticks were collected from the foci of infection in humans and domestic animals. Genetic markers of rickettsiae were detected using real-time polymerase chain reaction followed by species identification.

RESULTS: In total, nine ixodid tick species were identified from the collected specimens. Overall, the most abundant species were Haemaphysalis punctata (42.9%), Rhipicephalus sanguineus (20.8%), Hyalomma marginatum (15.5%), and Ixodes ricinus (12.8%). The collections were predominated by H. punctata in 2016 (75.5%), H. marginatum in 2017 and 2021 (58.2% and 24.6%, respectively), I. ricinus in 2018 (59.5%), and R. sanguineus in 2019 (47.9%). The DNA of eight spotted fever group rickettsiae species, including R. conorii, R. massiliae, R. sibirica subspp. mongolotimonae, R. slovaca, R. aeschlimannii, R. monacensis, R. helvetica, and R. raoultii were detected in the collected ticks. R. conorii was found in R. sanguineus and H. marginatum. For the first time on the Crimean Peninsula, R. massiliae was detected in R. sanguineus; R. slovaca in Dermacentor marginatus, H. marginatum, H. punctata, R. sanguineus, and I. ricinus; R. mongolotimonae in H. marginatum and R. sanguineus; and R. helvetica in I. ricinus. The greatest diversity of the spotted fever group rickettsiae was recorded in R. sanguineus and H. marginatum.

CONCLUSION: This study established the role of ixodid ticks in the circulation of eight species of spotted fever group rickettsiae on the Crimean Peninsula. They included R. conorii, R. massiliae, R. slovaca, R. raoultii, R. aeschlimannii, R. mongolotimonae, R. monacensis, and R. helvetica. The DNA sequences of R. conorii, R. massiliae, R. slovaca, and R. raoultii were deposited in the GenBank database. These findings on the quantitative and species composition of the ixodid fauna, tick infection rates, and genetic diversity of the detected rickettsiae highlight the need to expand laboratory capabilities, apply a risk-oriented approach, and implement corrective measures to the epidemiological surveillance system of spotted fever group rickettsioses on the peninsula.