Molecular genetic monitoring of natural focal of tick-borne infections in the epidemic season of 2018 revealed infectiousness of ixodid ticks causative agents of tick-borne encephalitis (0.58% of cases), Lyme disease (31% of cases), human monocytic ehrlichiosis (1.6% of cases) and granulocytic anaplasmosis (3.9% of cases) is registered and also co-infections of ticks by these infections (2.9% of cases) is revealed in natural and anthropourgic foci (B. burgdorferi s.l.+A. phagocytophilum, B. burgdorferi s.l.+E. chaffeensis/E. muris and B. burgdorferi s.l.+tick-borne encephalitis virus). The major epidemiological importance of ticks of the species I. persulcatus is found, their share being 87,6%. The majority of patients being bitten by a tick were from the southern and southeast areas of Primorye. Contamination of ticks with Borrelia was revealed not only in I. persulcatus, but also in ticks of the Haemaphysalis and Dermacentor. The infectiousness of ticks of B. burgdorferi s.l. (42,3%), tick-borne encephalitis virus (7,7%) and A. phagocytophilum (15,4%) was highest on Russky Island.

We have shown the levels of specific antibodies that can neutralize different strains on the virulence of the virus of tick-borne encephalitis (TBE). Specific immunoglobulin with its titers of 1:100, 1:400 и 1:3200 and two TBEV strains with its doses 3 lg TCID50/ ml (Dal negorsk - highly pathogenic, Primorye-437 - not pathogenic for humans). Evidential basis of the activity of residual virus has been obtained in vitro and in vivo in 3, 24, 48 and 72 hours after infection cells of culture PK and mice neinbrednyh by the test samples. Immunoglobulin does not have a protective effect, if its titer is 1:100; inhibits low virulent strain (P-437), but not Dal negorsk one, if its titer is 1:400; and inhibits both strains, it its titer is 1:3200. Regarding the models of different TBE virus strains, this article suggests new approaches to studying the efficacy of specific vaccine prophylaxis and individual prescription of the amount and terms of revaccination for tick-borne encephalitis.

No abstract

Vaccines for prophylactic immunization provide the most reliable and effective protection against the vast majority of infectious diseases. Tick-borne encephalitis (TBE) represents a high-priority medical issue at the territory of the Eurasian continent. Of great importance is assessing a role of distinct antibody titers especially low titers, observed quite often in vaccinated individuals, sometimes posing obstacles in determining a threshold of seropositivity as well as the level of specific protection against TBE virus. We aimed at obtaining data to assess antiviral activity of virus-specific antibodies with distinct titer levels based on the in vitro, ex vivo and in vivo experimental studies with a highly virulent Far-Eastern strain of tick-borne encephalitis virus. The in vitro, ex vivo and in vivo comprehensive experimental studies with a highly virulent Far-Eastern strain of tick-borne encephalitis virus (TBEV) were conducted and the dynamics of antiviral activity of virus-specific antibodies at variable titers (1:100–1:3200) was measured (timeframe ranged within 1–96 hours p.i.) to provide a rationale for evaluating the antiviral immune response. It was found that the in vitro experiments demonstrated that the IgG at 1:100 titer exerted a weak anti-TBEV neutralizing effect at all time-points examined. The IgG 1:400 titer caused a 2 log PFU/mL decline in TBEV Dal strain yield at 72 h post-infection, whereas at 1:3200 titer it completely suppressed TBEV replication throughout the observation period. The ex vivo experiments with blood serum obtained from vaccinated subjects demonstrating a range of TBEV antibody titers (sera from vaccinated individuals with varying anti-TBEV antibody titers) and in vivo (outinbred white mice) experiments revealed a delayed virus elimination for antibody titers at 1:100 and 1:200 as well as rapid virus elimination (1–2 days p.i.) for antibody titers greater than 1:400. Thus, antibody titer at 1:400 may be considered as the universal anti-TBEV protection threshold. In order to properly conclude regarding the revaccination schedule it is advised to start with testing blood serum for durability of anti-TBEV immune response. Subjects with TBEV antibody titers at 1:100 and 1:200 should be strongly recommended to undergo a mandatory revaccination. Such an approach is believed to be the most effective way toward enhancing efficacy of vaccine-mediated protection against TBE.

The aim of the work is to show the ecological, epizootological and epidemiological significance of ixodic ticks in the distribution and circulation of tick-borne pathogens in the south of the Far East. Methods. The material for the study was collected during an expedition conducted in the spring and summer of 2018 on five routes: in the northwestern territories of the Primorsky Territory (Spassky District, Lesozavodsky City District) and in the northern territories (Krasnoarmeysky District). 830 copies of ixodic ticks were collected. 187 samples were studied using real-time polymerase chain reaction (PCR-RT). Results. Of the total number of ticks collected, route 1 accounted for 24.7 %, 2 - 17.4 %, 3 - 19.5 %, 4 - 23.0 %, 5 - 14.8 %. It was shown that ticks I. persulcatus (73.1 ± 4.3) - (95.9 ± 1.5) % were the dominant species on all studied routes except route 3. On all routes, tick infection by I. persulcatus was most often observed, in which RNA tick-borne encephalitis virus was detected in 2 cases (1.9 %), DNA B. burgdorferi s. l. - in 40 (37.7 %), DNA B. miyamotoi - in 1 (0.9 %), DNA A. phagocytophilum - in 7 (6.6 %), DNA E. chaffeensis / E. muris-FL - 1 (0.9 %). In ticks of the Haemaphysalis genus, pathogens were detected only in H. japonica: - in 1 pool (1.2 %), DNA of R. heilongjiangensis - in 3 (3.7 %). Besides in 6 pools of ticks I. persulcatus, mixes of genetic markers of DNA of B. burgdorferi s. l. with various pathogens were detected. Conclusions. The data obtained indicate a different degree of infection of ixodic ticks with tick-borne pathogens, which indicates the need for monitoring studies with a wide coverage of all territories in the south of the Far East.