Sensitive analysis of genetic heterogeneity of adenovirus types 3 and 7 in the Soviet Union.

An analysis of adenovirus strains isolated in the Soviet Union from 1976 to 1988 revealed four genome types of adenovirus type 3 (Ad3), i.e., Ad3a4, Ad3a9, Ad3a10, and Ad3a11, and four genome types of adenovirus type 7 (Ad7), i.e., Ad7p, Ad7a, Ad7a(1-5), and Ad7f1, identified with the DNA restriction enzymes BamHI, BglII, and HindIII. Three of them, Ad3a10, Ad3a11, and Ad7f1, are newly discovered. The genetic heterogeneity of adenoviruses was examined with restriction endonuclease Cfr13I with a 4-base recognition cleavage site. Eighteen different restriction patterns were identified among 21 selected Ad3 strains after cleavage of DNA with Cfr13I. Eight different subtypes were identified among 20 Ad7 strains by the same technique. For estimation of the relationships among these genome subtypes, pairwise analyses of comigrating DNA restriction fragments from isolates of Ad3 and Ad7 were done after digestion with Cfr13I or with restriction endonucleases recognizing DNA sequences of 6 bp. Surprisingly, the results were very discrepant.

Studies of natural population variability of parainfluenza viruses during their epidemic circulation.

The population of circulating serotype 3 parainfluenza virus strains isolated in different years proved to be sufficiently polymorphic concerning its antigenic and biological features as well as their virulence for newborn hamsters. The highly virulent strain population appeared to have an antigenic pattern different from that of the prototype strain. The epidemic caused by it in groups of school and preschool children was more intensive as compared to that induced by avirulent strains population.

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.

Dynamics of some genetic marker changes of respiratory-syncytial virus strains circulating among nursery-school children.

Respiratory-syncytial (RS) virus strains circulating during several years appeared polymorphic in respect of two genetic markers: the regression coefficient of infectious activity (RCIA39) characterizing the isolates by their reproduction in tissue cultures at supraoptimal temperature (39 degrees C) and the regression coefficient of neutralization indices (RCNI) characterizing the degree of sensitivity of the strains to antibodies. High-yield RS viruses were more often isolated from children frequently afflicted by the disease, moderate-yield viruses from moderately sick children, while low-yield or none-yield (at 39 degrees C) strains were isolated from rarely afflicted children. On the other hand, RS strains of low reactivity with prototype antibodies were mainly found in often or moderately sick children and the high-reactive ones in rarely sick children. The variability of the RS virus population was continuous, which is consistent with the uninterrupted course of the epidemic process in the nursery-school community. A change of the RCIA39 marker was observed in nearly 50% of strains already after 1 1/2 to 2 months, but most frequently within 5-6 months from the end of disease. The changes of growth intensity at 39 degrees C followed the pattern: high----moderate----low----none, however, in the next epidemic season these properties showed reversion in an opposite direction.

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.

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%).