Detection of Tick-Borne Pathogens in Ixodid Ticks Removed from Humans in the Khabarovsk Krai during the Epidemic Seasons of 2017–2024

Introduction: The Khabarovsk Krai is home to multiple natural foci of tick-borne diseases noted for persistence and cyclicity. Of its 19 administrative territories, 16 are endemic for tick-borne encephalitis and other tick-borne diseases. In view of the above, monitoring of abundance, species composition, and infection rates in ixodid ticks is an essential element of epidemiological surveillance of this group of infections.
Objective: To analyze infection rates in embedded ixodid ticks removed from humans in the Khabarovsk Krai in 2017–2024.
Materials and Methods: In order to establish infection rates in ticks during the epidemic season (April–October) of the years 2017 to 2024, we tested 16,863 engorged ixodid ticks removed from humans in the Khabarovsk Krai. The enzyme-linked immunosorbent assay was used to detect the tick-borne encephalitis virus antigen while the real-time polymerase chain reaction detected the DNA of Borrelia, Rickettsia, Ehrlichia, and Anaplasma. Real-time RT-PCR was used as a nucleic acid amplification test.
Results: Of the ticks tested, 76.0 % were of the genus Ixodes, 7.6 % were of the genus Haemaphysalis, 3.1 % were of the genus Dermacentor, and 13.3 % were ticks of unspecified genus. Genetic material of tick-borne pathogens including B. burgdorferi s.l. complex was detected in 39.2 %, B. miyamati DNA – in 6.6 %, A. phagocytophilum DNA – in 6.2 %, E. muris / E. chaffeensis DNA – in 5.72 %, R. sibirica DNA – in 0.4 %, and R. heilongjiangensis DNA – in 21.5 % of the samples. Multiple (four or more) tick-borne pathogens were a more frequent finding in ixodid ticks.
Conclusion: Results of the annual monitoring of infection rates in ixodid ticks prove the presence and activity of combined natural foci of tick-borne diseases in the Khabarovsk Krai.

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