Population variability of serotype 3 adenoviruses circulating in the U.S.S.R.

Composition analysis of natural populations of adenovirus serotype 3 (Ad 3) strains--based on samples selected out of 170 strains isolated in different regions of the U.S.S.R. from 1976 to 1981--has demonstrated their inhomogeneity with respect to cytopathogenicity and haemagglutination activity. The strains were classified into 3 groups: low, medium and highly cytopathic. The cytopathogenicity of the strains appeared to be a rather variable feature dependent on regional climate and on seasonal complexity. In summer low cytopathogenic viruses predominated. The epidemic activity of circulating adenoviruses (proportion of adenoviruses in the aetiology of acute respiratory disease) correlated with the level of their cytopathic activity.

Some regularities in variations of respiratory syncytial virus strains during their epidemiological circulation.

Among respiratory syncytial (RS) viruses circulating in the territory of U.S.S.R., strain variations were observed based on the differences in activity of virus reproduction in human embryo kidney cell cultures at 39 degrees C and in virus sensitivity to antibodies. Mathematical expression of the correlation between these two genetic markers made it possible to classify the new isolates of RS virus into three groups differing in their virulence, namely high, mild and low virulent strains. Populations of RS virus strains varied depending on the epidemic season: during the first period (1976-1977) predominated the high virulent (52-78%) while during the second period (1977-1978) the mild virulent (55-65%) strains. The third period (1978-1979) was characterized by the circulation of a mixture of mild and low virulent strains. In summer low virulent virus strains prevailed (56-89%).

Antigenic and biological criteria of differentiation of the newly isolated strains of respiratory syncytial virus.

Respiratory syncytial (RS) virus strains isolated in different years varied by their antigenic and biological properties. The lowest degree of relatedness was found between the "street" virus and the prototype Long strain; the highest occured among the isolates from a given isolation period. Based on the mean indices of efficiency of the virus reproduction in human embryo lung (HEL) cells at 37 degrees C and 39 degrees C as well as on the degree of virus sensitivity to reference antibodies, the isolates from various years could be divided into three groups, namely high, mild and low virulent strains. The incidence of RS virus infections in children depended on the strain characteristic of virus population circulating in a community of children during the long-term observation period of 1976-1979. Cyclic variation was found in isolation rates of RS viruses; the duration of each cycle in different years ranged from 21 to 41 days. The variability of isolation cycles and the frequency of RS virus reinfections were closely related to the biological characteristics of circulating virus strains.