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The research presents data on evaluation of immunity levels to tick borne encephalitis virus in unimmunized population of the Amur region during 2011-2017.The highest levels of antibodies were detected in population inhabiting middle and south taiga landscape zones. It should be noted that high antibody levels to tick borne encephalitis virus found in local residents show high frequency of contact with infected carriers as well as possible cases of inapparent form of the infection. The form of affiliation to a certain landscape zone well as the quality of territorial development as has considerable importance on the formation of herd immunity to tick-borne encephalitis virus.

Tick-borne encephalitis (TBE) is a natural focal viral neuroinfection vastly spread in the mid-latitude climate zone of theEurasia. Lethal cases and disability related to TBE determine its high epidemiological significance as well as underlie undiminished attention to prevent it in endemic territories. At the same time, TBE epidemiologic features significantly differ in various geographic areas. Importantly, Republic Sakha (Yakutia) is not among TBE endemic areas in theRussian Federation. However, in the last decade an increased incidence of ixodic tick bites was registered in the Republic Sakha. A pattern of pathogen-specific population immunity is one of the most valuable criteria for assessing magnitude of epidemic process in TBE foci. Hence, our study was aimed at assessing natural herd immunity TBEV in Republic Sakha associated with elevated incidence of tick bite visits. Here, we analyzed the data regarding the rate of tick attacks in the period of 2001–2007 in Republic Sakha. Residents and individuals unvaccinated against TBEV in the city ofYakutskas well as various administrative regions were examined to record the peak incidence of tick attacks. It was found that a range of the administrative regions recording with registered of ixodic tick attacks and elevated incidence of tick bites was expanded. Moreover, the top incidence of tick bites was annually recorded in the south regions of the republic Aldanian, Neryungri, Olyekminsk, Leninsk, Khangalassky districts, city ofYakutskand its suburbs. Furthermore, TBEV-specific immunoglobulins were detected in 5.7±0.68% of the residents examined suggesting about contacts with the pathogen. In addition, the peak count of seropositive people (8.9±1.85%) was identified in Namsky district located in the central part of the republic. Overall, detection rate of TBEV-specific antibodies among general adult population (6.9±0.95%) was significantly higher compared to those observed in children (3.9±0.89%, р < 0.05). no significant differences in urban (5.8±1.12%) vs. rural population (5.63±0.84%) was found.

Introduction. At present, the areas endemic for tick-borne encephalitis (TBE) tend to expand. Monitoring of TBEV antibody detection rates in the population of non-endemic areas in order to adopt timely measures for specific and non-specific disease prevention thus acquires particular importance. The Tuguro-Chumikansky District is not among the endemic areas of the Khabarovsk Krai. Yet, the rise in the number of people seeking medical attention for an ixodes tick bite and TBE rates in the local population has been registered recently. Our purpose was to establish the level of natural herd immunity to the tick-borne encephalitis virus in the population of the Tuguro-Chumikansky District. Materials and methods. We conducted a serological survey among unvaccinated permanent residents of 6 villages of the study district. Results. The highest TBEV antibody detection rates were registered in the examined residents of the villages of Tugur (61.3 ± 8.75%) and Udskoye (51.4 ± 8.22%). On the whole, specific immunoglobulins for the tick-borne encephalitis virus were found in 29.4 ± 2.26% of the subjects, thus indicating that the locals have contacts with infected vectors or have possibly suffered from the inapparent (subclinical) infection. Discussion. The established immunoglobulin G detection rates and immunity levels to TBEV may show that the population of the Tuguro-Chumikansky District is involved in the epidemic process. A further increase in the number of people bitten by ticks can lead to an increase in the registered TBE incidence in the district making it yet another regional area endemic for the disease.

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