Precursor genes of future pandemic influenza viruses are perpetuated in ducks nesting in Siberia.

Influenza A viruses of different subtypes were isolated from fecal samples of ducks in their nesting areas in Siberia in summer from 1996 to 1998. Phylogenetic analysis of the NP genes of the isolates in Siberia and those in Hokkaido, Japan on their flyway of migration from Siberia to the south in autumn revealed that they belong to the Eurasian lineage of avian influenza viruses. It is noted that the genes of the isolates in Siberia are closely related to those of H5N1 influenza virus strains isolated from chickens and humans in Hong Kong in 1997 as well as to those of isolates from domestic birds in southern China. The results indicate that influenza viruses perpetuated in ducks nesting in Siberia should have contributed genes in the emergence of the H5N1 virus in Hong Kong. Vaccine prepared from avirulent A/duck/Hokkaido/4/96 (H5N3) influenza virus was potent enough to protect mice from challenge with lethal dose of the pathogenic H5N1 virus [19]. Intensive surveillance study of aquatic birds especially in Siberia is, therefore, stressed to provide information on the future pandemic influenza virus strains and for vaccine preparation.

[Perfection of methodical approaches to designing vaccines against tick-borne encephalitis]. / Sovershenstvovanie metodicheskikh podkhodov k konstruirovaniiu vaktsiny protiv kleshchevogo éntsefalita.

The protective properties of experimental vaccine against tick-borne encephalitis (TBE) were studied. The vaccine was prepared by conjugating colloid gold with soluble TBE antigen. The protective properties of experimental and commercial vaccines were compared by the mean survival time and protection coefficients after one and three vaccinations of mice infected in doses of 100,000 and 10,000 LD50. In animals immunized with experimental vaccine the protection coefficient and mean survival time were, respectively, 1.3-1.5 times and 10-30% higher than in mice immunized with commercial vaccine. Assessment of the therapeutic activity of antibodies induced by the experimental and commercial vaccines after 1 and 3 immunizations showed the mean survival time to be 1.2-1.7 times longer in animals injected antibodies from mice immunized with the experimental vaccine.

[Isolation of strains of Negishi virus in Khabarovsk Territory]. / Vydelenie shtammov virusa Negishi v Khabarovskom krae.

Two virus strains isolated from Aedes vexans nipponi and Aedes vexans vexans in 1976 and 1978, respectively, in Khabarovsk Territory were identified as Negishi virus. Among 176 human sera, 22.7% were found to contain complement-fixing antibodies to Negishi virus soluble antigen.

[Concentration of the Venezuelan equine encephalomyelitis virus in a 2-phase system of water-soluble polymers]. / Kontsentratsiia virusa venesuél'skogo éntsefalomielita loshadei v dvukhfaznoi sisteme vodorastvorimykh polimerov.

A three-step concentration of Venezuelan equine encephalomyelitis (VEE) virus from tissue culture fluid was carried out in a two-phase system of polyethyleneglycol (PEG)--sodium dextran sulphate (SDS). The concentration method was based on the dependence of virus distribution coefficient upon NaCl content in the system which allowed alternating transfer of the virus from one phase of the system into the other. The infectious activity of the virus increased approximately 100-fold after the first step, 190-fold after the second, and 300-fold after the third step. The process of concentration was accompanied by purification of virus preparations. This was indicated by the results of immune electron microscopy which allowed visual observation of accumulation of the virus material in the preparations and decrease of the content of cell membrane elements. SDS was removed from virus preparations by precipitation with 3 M KCl solution in the cold, the procedure having no effect on the infectious activity of the preparations.

Differentiation in the complement fixation test of the viruses of tick-borne encephalitis complex by means of a type-specific soluble antigen.

Highly type-specific soluble antigens (SA) of viruses of the tick-borne encephalitis (TBE) complex were obtained by treatment of the sucrose-acetone antigens with 8 mol/l urea. Each SA reacted with the homologous serum only. The serum to SA of strain Sofyin and of Omsk haemorrhagic fever virus distinguished the TBE complex representatives; the difference between homologous serum titres was in the range of 4-5 two-fold dilution steps.