Genetic evidence for variant selection in the course of dilute passaging of mumps vaccine virus

Mumps vaccine viruses, Leningrad-3 (L-3) strain, harvested at the 8th (8P) and 38th (38P) passage levels, were compared by nucleotide sequencing of the fusion (F) and the phosphoprotein (P) genes, and for replication efficiency in cell culture. Sequencing revealed only one clear base substitution throughout the entire F gene, and no substitutions in the variable 183-nucleotide-long region of the P gene. However, the 8P virus, unlike the 38P variant, contained multiple "ambiguous" nucleotide regions, i.e., additional bases positioned at the level of the principal ones. The 38P variant replicated faster and appeared more homogeneous by its plaque character compared to the 8P virus. The results indicate that the 8P progenitor virus consisted of more than one viral variant and that one of these was selected on repeated passage due to its higher replication efficiency.

Experimental-scale measles and mumps vaccine production on microcarrier-grown cells

Small-scale measles and mumps virus propagation in microcarrier-grown cells was studied to assess putative advantages over conventional roller-type virus propagation. Significantly higher virus yields could not be attained with microcarrier cultures in cell stirrers, therefore making the advantages purely technological. The pattern of measles virus production was slightly different for the three types of microcarriers used. Experimental measles and mumps vaccine lots obtained met vaccine quality control requirements.

Laboratory markers for over-attenuation of mumps vaccine virus

The properties of mumps vaccine virus (Leningrad-3 strain) gradually changed upon passaging in quail embryo fibroblasts, the substrate normally used for mumps vaccine production in the USSR. Alterations were extremely noticeable in the over-attenuated (38th passage) virus variant, and involved (a) poor, if any, antibody response in guinea-pigs, (b) turbid plaque formation, (c) lack of expression in cell culture of fusion protein and reduced expression of polymerase protein, and (d) enrichment by abnormally small, fusion-protein-deficient virus particles. Two other laboratory strains exhibited a similar trend to over-attenuation, though after variable passage numbers. Due to a good inter-correlation, every test (namely, inoculation of guinea-pigs, plaque assay, protein analysis, or immune electron microscopy) is indicative of mumps vaccine over-attenuation and hence might be valuable in seed virus quality control.

[Comparative study of the sensitivity of the serological methods used in detecting mumps virus antibodies]

Six different methods were used for examinations for the presence of antibodies to mumps virus in 43 sera of donors varying in ages from 18 to 58 years. Judging by the percentage of positive results, most sensitive tests included: radial hemolysis (95.3), neutralization (88.4-81.4), immunofluorescence (83.7). Comparison of the results obtained in these tests revealed high correlation coefficients of antibody titres. The lowest number of positive results was obtained in lectin-neuraminidase test and hemagglutination-inhibition test (51.2% and 32.6%, respectively).

Study of mumps virus invasiveness in monkeys

Invasiveness of mumps virus strains, differing in the degree of attenuation was studied in green and Macaca mulatta monkeys infected either into salivary glands or intramuscularly. Peripheral infection with all strains under study resulted in their penetration into CNS irrespective of the attenuation degree. Specific morphological changes were observed in the brain of monkeys as confirmed by detection of virus antigen using fluorescent antibodies (FA) staining. Morphological changes and time of virus antigen detection in the brain differed depending on the neurovirulence of the strains based on different degree of their attenuation.

[Results of a study of live mumps vaccine from strain L-3 produced by the Moscow research institute for viral preparations. Characteristics of the vaccine]

For some years the Moscow Research Institute of Virus Preparations carried out studies concerned with the elaboration of conditions for production and control of mumps vaccine from the Leningrad-3 (L-3) strain under experimental production conditions. Twenty nine batches of the vaccine were prepared, tested and studied in extensive field trials. The paper presents the optimal conditions for the preparation of the live mumps vaccine from the L-3 strain in Japanese quail embryo cell cultures. In monkey experiments the L-3 strain was shown to have no neurovirulence. The system of biological control for the mumps vaccine permits to release the preparation meeting the current requirements for safety of live tissue culture parenteral vaccines. The data on the stability of the mumps vaccine from the L-3 strain are presented.

Morphological differences in the central nervous system and organs of monkeys inoculated intracerebrally with virulent and attenuated strains of mumps virus

The degree of attenuation of mumps virus was studied in intracerebrally inoculated Macaca mulatta monkeys. The virulent Leningrad-3 strain and its attenuated variant as well as the attenuated Sophia-6 strain were used. The nature of pathological alterations in the neurons pointed to neurotropism of only the virulent strain. Morphological changes caused by attenuated and virulent strains in the brain structures, in the epithelium and glandular structures of the salivary glands differed considerably and may be used as a kind of markers of neurovirulence and the degree of attenuation of mumps virus strains.