[Atenuated variant "M" of Rickettsia burneti as a possible live vaccine against Q-fever].

Abstract : During the past few years a number of experimental studies appeared in Soviet and foreign literature reporting variability phenomena among many species of rickettsiae pathogenic to humans. The present state of the problem of variability of rickettsiae is described thoroughly by P. F. Zdrodovskiy (1959) in his review of Soviet and foreign research. Among the experimental works related to the variability of rickettsiae, those studies deserve the most attention which show the possibility of a considerable and stable loss of virulence. This may result either from splitting-off of rickettsiae during cultivation on chick embryos (Clavero and Gallardo, 1948), or from prolonged, continuous passing of rickettsiae under special conditions, as for example through lice.