Clinical and Epidemiological Manifestations of Ixodic Tick-Borne Borreliosis Foci in the Tomsk region

Abstract

Relevance. According to official data, in 2020 in Russia, Ixodic tick-borne borreliosis took the leading position in the prevalence and registration frequency among tick-borne infections, which amounted to 38.5% of all cases of natural focal transmissible infections. In the Tomsk region for many years, the average long-term incidence of Ixodic tick-borne borreliosis exceeds the Russian one by more than 3 times. Aim. Identify features the features of the clinical and epidemiological manifestations of the Ixodic tick borne borreliosis foci in the Tomsk region; to identify priority areas for carrying out problem-oriented research in the field of ecology, epidemiology and the clinic of borreliosis infection in the Tomsk region. Materials and methods. The material for the study was the data of the federal statistical observation form «Information on infectious and parasitic morbidity» for the 2015-2020. The materials of 713 cases of Ixodic tick-borne borreliosis disease and more than 125 thousand appeals to medical organizations of the region regarding the tick bites, registered in official registration forms, were studied. As part of the annual epidemiological monitoring for a six-year period, 1200 specimens of Ixodid ticks collected in natural biotopes of the Tomsk region were examined for the presence of Borrelia DNA, depending on their genus (Ixodes and Dermacentor). DNA detection of Borrelia burgdorferi sensu lato complex (B. burgdorferi, B. garinii, B. afzelii) and B. miyamotoi was performed by real-time PCR. Results. The high number of ixodid ticks in local areas of natural biotopes (up to 200.0 specimens/km at the height of the epidemiological season), as well as the failure to comply with personal prevention measures, determines a consistently high rate of referral of the population of the Tomsk region to medical organizations due to tick bites. The number of requests annually averages 20.8 thousand. As a result of an annual study using PCR tests of ticks taken from people who applied to emergency prevention centers, Borrelia DNA was detected on average in 40% of samples; blood samples from individuals affected by tick bites were positive on average in 3.7% of cases. In the period 2015-2019 spirochetes B. garinii and B. afzelii were most often found in the tissues of ixodid ticks. Since 2020, the species Borrelia miyamotoi has been included in the list of pathogenic borrelia species to be monitored in the Tomsk region – spontaneous infection of ticks (Ixodes) was 3%. The maximum values both in the number of patients with ixodic tick-borne borreliosis and in the density of infections per 10,000 hectares (90-110 cases) are observed in the south of the Tomsk region (Asinovskyi, Kozhevnikovskyi, Krivosheinskyi, Tomskyi, Shegarskyi districts, the city of Tomsk). In the epidemic season of 2020, the number of laboratory-confirmed cases of non-erythema ixodic tick-borne borreliosis was more than 2.5 times higher than the number of diseases with skin manifestations. Conclusion. The large number of ixode mites in natural biotopes, the high degree of their infection with pathogenic spirochetes indicate the presence of active natural foci of ixodic tick-borne borreliosis in the Tomsk region. The study of the genotypic diversity of pathogenic borrelias in relation to the species diversity of vectors, the analysis of the clinical manifestations of different etiological variants of tick-borne borreliosis (mono- and mixed infections), as well as the development of an algorithm for differential diagnostic search and a model for predicting the outcomes of the infectious process in tick-borne borreliosis and mixed infections are priority directions of problem-oriented scientific research in Tomsk region.