Analysis of the Epidemiological Situation in Natural Foci of Siberian Tick-Borne Typhus in the Territory of the Minusinsk Basin (Krasnoyarsk Territory and the Republic of Khakassia)

The aim of the study was to assess the epidemiological situation and to characterize the potential epidemic hazard in the foci of Siberian tick-borne typhus (STT) in the Minusinsk Basin (Krasnoyarsk Territory and the Republic of Khakassia).
Materials and methods. The analysis of the STT incidence rates per 100 thousand population in administrative districts of the Minusinsk Basin between 2013 and 2022 was carried out. Ticks (n=182) collected on a flag in the territory of the Minusinsk basin and sectional material from the patient were studied using the PCR method with a set of genus- and species-specific primers to identify various types of Rickettsia followed by sequencing of the obtained amplicons.
Results and discussion. The average long-term incidence rate of STT in the Minusinsk Basin is 11.8 ⁰/₀₀₀₀ (95 % CI 11.4–12.2). The maximum incidence of STT occurs in May and June, which is determined by early seasonal activity of the main vector, the Dermacentor nuttalli tick. The PCR analysis has revealed a total DNA detection of Rickettsia at 79.2 %. Rickettsia sibirica, R. helvetica and R. raoultii DNA has been detected in D. nuttalli. Haemaphysalis concinna contains DNA from R. heilongjiangensis, R. sibirica and R. raoultii. In the study of the Ixodes persulcatus ticks, Candidatus R. tarasevichiae has been identified in all positive samples. D. silvarum specimens contained DNA from R. sibirica, R. raoultii, and Ca. R. tarasevichiae. DNA from R. sibirica subsp. sibirica was identified in sectional material from a STT case with fatal outcome. The activation of the epidemic process in in the Minusinsk Basin (Krasnoyarsk Territory and the Republic of Khakassia) is due to epidemiological risks (high activity of D. nuttalli ticks and the total rickettsiophority of R. sibirica vectors, documented fatal cases, circulation of highly virulent strains of R. sibirica) with their transition from potential to actual.

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