Abstract
Whilst the volume of literature concerning rubella virus has increased markedly during recent years, few authors have compared the properties of strains of varied origin and history. In the main, interest has centred on the biological characteristics of the attenuated strains of rubella and the modification of such properties during loss of virulence for man. A study of the plaque morphology in GL-RK[1]3 cells, of some 36 strains from pre and post-natally acquired infection was undertaken. The strains included laboratory adapted, highly passaged and freshly isolated material with little or no history of culture in vitro. It was found that in the main, low pass strains showed a typical small plaque form but two freshly isolated strains with large plaque type were also encountered. The laboratory passaged strains showed a range in plaque morphology from small to large which did not appear to be dependant on the tissue selected for propagation of the virus. A brief study of the influence of tissue culture passage on the plaque morphology of selected strains yielded evidence of two systems of change; the first being a gradual transition from a small to large plaque, whilst the second appeared to be closer to a selection process, the new plaque type emerging and becoming predominant. Six representative strains of rubella were selected for further study. Growth of virus and production of haemagglutinating antigen in several cell culture systems was compared and the results suggested that the previous passage history of a strain could influence its potential for growth in cell culture. The thermal stability of these strains was also investigated and the two isolates from congenitally infected infants were shown to differ in their pattern of inactivation. All of the strains were shown to be immunogenic in rabbits, and the antisera thus produced were used in cross haemagglutination inhibition and neutralization studies. Apparent anomalies were encountered with the antisera produced in response to the Cendehill strain. It was not possible to demonstrate haemagglutination inhibiting antibodies against some of the strains in spite of the fact that these were present to high titres against other strains of rubella. Examination of the kinetics of homologous and heterologous neutralization showed some difference between the strains and the existence of two particularly antibody sensitive strains.