Baikalian Highway as a High-Risk Area for Transmissible Tick-Borne Infections
Authors:   Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, Mel’nikova O. V. , Adel’shin R. V. ,   Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, Vershinin E. A. ,   Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, Lopatovskaya K. V. ,   Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, Trushina Yu. N. ,   Bokhan District Hospital, Andaev E. I. ,   Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor
Published: April 2024

The results of long-term monitoring of the taiga ticke I. persulcatus abundance and its infection rate with tick-borne encephalitis virus and bacteria of genus Anaplasma, Borrelia, Ehrlichia and Rickettsia in forests along the Baikalian highway (road No 25К-011 Irkutsk region, Russia). The ticks’ abundance varied in space and time from complete lack on the registration route up to 339 ticks per flag-hour. The dynamics during study period (2005-2022) had three waves of ups and downs. The maximum of long-term average seasonal activity occurred at second and third decade of May. The average numbers of ticks increased as distance from the city grew. The analysis with the help of multiplex test system for four infections (tick-borne encephalitis virus, Anaplasma, Borrelia, Ehrlichia) showed marker at least of one pathogen in 57 % of specimens, different mixes of two and more co-infections – in 16.3 %. From 10 variants of co-infections found in this sample, the most prevalent were combinations of Borrelia, Ehrlichia and Anaplasma (74.7 % of double and 7.5 % triple «mixes»). Least often, the ticks were co-infected with tick-borne encephalitis virus in combination with Ehrlichia and Anaplasma (0.5 % each). In average the ticks most often contained the genetic material of Rickettsia (68.1±2.94 % of tested samples) and Borrelia, (48.3±1.30 %), then, in descending order, – Anaplasma, (13.5±0.88 %), Ehrlichia (9.5±0.76 %) and tick-borne encephalitis virus (3.0±0.47 %). Despite the low proportion of ticks with the virus in natural foci, 68.5 % of the persons, bit by infected ticks on the territories along Baikalian highway, became ill with tick-borne encephalitis. Conversely, with a wide prevalence of Rickettsia and Borrelia in ticks, the tick-borne rickettsiosis was diagnosed in 3.1 % of the victims and borrelioses – in 28.4 %. No significant differences have been revealed between the infection rate of adult ticks and nymphs, and between males and females, except for Borrelia, which more often have been found in females than in males (51.9 % versus 45.7 %). The tendencies of the pathogens prevalence in time and different plots of territory studied and risks for human infection have been revealed. It was shown than more than a half of human tick-borne encephalitis, tick-borne borrelioses and tick-borne rickettsiosis contracting occurs in the closest suburbs of Irkutsk – up to the 30th km of the highway, where the ticks’ abundance is lower, than in more distant areas, in other words are more to do with human behavioral factor than with the vector’s activity.