STUDY OF THE ANTIGENIC STRUCTURE OF VACCINE STRAIN M OF RICKETTSIA BURNETI,
ARMY BIOLOGICAL LABS FREDERICK MD
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In 1950--1953 changes were established in the antigenic structure of Rickettsia burneti, depending on the conditions of cultivation, and two phases were revealed. These were named variation phases I and II respectively. Since then the mutability of Rickettsia burneti has been studied by many Soviet and foreign investigators. Vaccine strain M of Rickettsia burneti possesses an antigenic structure which is similar to the structure of phase II of virulent strains, but in contrast to the latter vaccine strain M, does not cause the formation of complement-fixing antibodies to the antigen of phase I of rickettsia. The corpuscular antigen from strain M is highly active in the reaction of complement fixation and can be used for the exposure of antibodies to phase II of Rickettsia burneti. It can be assumed that the loss of pathogenicity by the virulent Grit strain and its conversion into an attenuated variant - strain M - is connected with the loss or change in the antigenic substance which is characteristic for phase I of rickettsia, i.e., with conversion into the pure phase II.