Transmissible tick-borne infections in the south of the Far East

Natural foci of tick-borne infections associated with tick-borne encephalitis virus (TBEV), borrelia (Borrelia burgdorferi sensu lato), including Borrelia miyamotoi, anaplasma, ehrlichia and rickettsia are widespread in the Primorsky Krai. The carriers of these pathogens are ixodid ticks. The population of Primorsky Krai meets with ticks in natural biotopes, as well as in anthropurgic foci. The aim of the study is to give a comparative assessment of the epizootic activity in the natural foci of transmissible tick-borne infections in the south of Primorsky Krai in the epidemic seasons of 2017–2020. In this periodixodid ticks (3778 samples), taken from humans in natural foci in the Primorsky Territory, were studied. The TBEV antigen was determined by enzyme-linked immunosorbent assay (ELISA), genetic markers of pathogens were detected by real-time polymerase chain reaction (RT-PCR). The incidence of tick-borne infections has been analyzed. Based on the results of monitoring the infection of ixodid ticks, we found that 26.9 % of the studied samples were infected with various pathogens of tick-borne infections. Low infection rate of TBEV in ixodid ticks and high infection with pathogens of a bacterial nature were established. TBEV antigen was detected in 30 cases (1.4 %), TBEV RNA was detected in 20 cases (0.7 %), Borrelia burgdorferis. l. DNA — in 820 cases (30.7 %), ehrlichia — in 64 (2.4 %), anaplasma — in 55 (2.1 %).Genetic marker of Rickettsia spp. was detected in 3 cases (0.9 %) out of 322 examined ixodid ticks, B. miyamotoi — in 26 cases (6.9 %) out of 373 examined samples. A positive correlation was noted between the incidence rates and the cases of detection of TBEV and Lyme borreliosis in ticks. The results obtained indicate the need for annual epidemiological monitoring of infections transmitted by ixodid ticks, to determine the real epidemic situation and the activity of the functioning natural foci transmissible tick-borne infections on the territory of Primorsky Krai.