We have presented a comparative analysis of morbidity and mortality in the tick-borne encephalitis (TBE) in the south of the Russian Far East in the period 1980 - 2014. In the period from 2008 to 2014 using the enzyme-linked immunoassay (ELISA) was examined 10,599 copies ticks or leukocyte fraction of blood (n = 5561) of people who indicate to the fact of tick bites. Blood samples and ticks positive in ELISA additionally examined by PCR and virus isolation. Under diagnosis of TBE cases in the 1980s resulted in lower figures morbidity and mortality artificially excessive to 39% (average 28%). In the 1990s there was a sharp rise in the incidence of TBE (median 15.3% mortality). In the 2000s there was a trend to a decrease in the number of cases and deaths (average case fatality rate of 6.3 -10.5%). The incidence rate for 35-year follow-up period ranged from 0.85 to 9.88 per 100 thousand population, mortality was 14.8 ± 0.7%. The degree of danger of the epidemic on TBE synchronously reflected in the rate of antigen detection of TBE virus in humans and ticks attached themselves. In the year’s high morbidity and mortality (in 2009 and 2010) antigen detection in ticks and in human blood reached a maximum. Isolated from the blood of these patients three TBE virus strains indicated that only a complete virus capable of replicating determines the variety clinical forms of the infection.
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.
Background: The discovery of a new viral disease called tick-borne encephalitis (TBE) in the Far East in 1937 triggered the thematic virology research on the Eurasian continent. The purpose of our study was to conduct a virological and epidemiological monitoring of tick-borne viral infections in the Primorsky Krai over an 80-year period. Materials and methods: Several hundreds of strains belonging to the viruses of the TBE complex (Flaviviridae family) and other families have been isolated; their biological, antigenic and molecular genetic characteristics have been studied. Results: The most complete picture of the Far Eastern population of the TBE virus was obtained in the 1990s based on whole genome sequencing of 50 TBEV strains isolated from patients with different clinical manifestations of the disease and from ixodid ticks. It was established that all the strains belong to the same Far Eastern subtype of TBEV with three clusters (Oshima-, Sofjin-, and Senzhang-). In 1972, the Powassan virus was first isolated from Haemaphisalis longicornis ticks on the Eurasian continent. Phylogenetic analysis based on the whole genome characteristics of the Spassk-9, Nadezdinsk-1991 and Partizansk-2006 strains, as well as the characteristics of five fragments of other Powassan virus strains, indicated that they all belong to the Powassan virus lineage I. The first comparative description of three strains Primorye-155-77, Primorye-20-79 and Primorye-185-91 of the Louping ill virus was given. A comprehensive study of the isolated Ozernoe strain of a deceased female patient enabled identification of the first clinical case of the lyssavirus disease in the Asian part of Russia. This strain is genetically close and has a common ancestor with the Irkut strain and is attributed to pathogens of the genus Lyssavirus, family Rhabdoviridae. Conclusion: Isolation of a highly pathogenic lyssavirus and several viruses of the TBE complex indicates the importance of such virology surveillance and proves the necessity of its continuation.
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