Current epidemiological situation of tick-borne encephalitis in an endemic region

Abstract

Objective. To analyze the main characteristics of the tick-borne encephalitis (TBE) epidemic process in the Altai Krai during the modern period (2000–2024) and to evaluate the effectiveness of specific and nonspecific prevention on morbidity. Methods. The study is based on state statistical reporting data (Form No. 2), Rospotrebnadzor reports, and the results of entomological and virological surveillance (PCR, whole-genome sequencing). The study employs retrospective epidemiological analysis, calculation of intensive rates, Spearman's correlation analysis (r), Z-test for significance (p), as well as autocorrelation and Fourier spectral analysis to assess cyclicity. Results. The long-term average TBE incidence in the Altai Krai was 2.41±0.32 per 100,000 population, which exceeds the national average (2.06±0.04) by 16.99% (p<0.001). By 2024, incidence decreased 5.78-fold (to 0.90±0.21). A 10-year cyclicity of incidence and a 6-year cyclicity of the abundance and virus prevalence of ixodid ticks are revealed. The proportion of severe TBE forms was 43.78±1.31%; 25 fatal cases were recorded (all unvaccinated). An inverse correlation is demonstrated between incidence and the volume of vaccination (r=-0.32; p<0.05), emergency seroprophylaxis (r=-0.59; p<0.05), and the area of acaricide treatments (r=-0.70; p<0.05). No significant differences in incidence between urban and rural populations are found (p=0.763). Conclusion. The modern period (2000–2024) is characterized by the stabilization of TBE incidence in the Altai Krai at levels close to the national average due to increased volumes of vaccination, seroprophylaxis, and acaricide treatments. The identified 6-year cyclicity of tick virus prevalence allows forecasting of incidence dynamics. The absence of urban–rural differences indicates a significant role of anthropurgic foci, which requires their additional monitoring. Recommendations are given on the use of the obtained data for planning anti-epidemic measures in endemic regions.