Experiments with the Cyprus strain of blue-tongue virus: multiplication in the central nervous system of mice and complement fixation

The virus of blue-tongue has been adapted to eggs by Alexander, Haig & Adelaar (1947). These authors made the important observation that the temperature of incubation has a profound influence on the virus content of blue-tongue infected eggs. Alexander (1947), furthermore, observed certain irregularities in titrations which he suggested might be explained as an interference phenomenon. Blue-tongue virus has since been successfully adapted to the brains of suckling mice, but adult mice are apparently resistant to this virus (Kaschula, 1953). During experiments on the physical properties of the Cyprus strain of bluetongue virus we were once more struck by the influence of temperature of incubation on virus titre. We also observed that the virus would persist in the brains of adult mice for many generations without eliciting symptoms. We therefore undertook further studies of this virus, particularly on quantitative aspects of its multiplication and to attempt to elucidate the reasons for the differences in titre resulting from different temperatures of incubation. It appeared possible, for instance, that at higher incubation temperatures in eggs and during multiplication in adult mouse brains as distinct from suckling mouse brains, virus multiplication may produce incomplete virus which under appropriate conditions might interfere nvith the formation of infective virus.