[Immunogenicity of an R. burneti strain isolated in Bulgaria].

The immunogenic properties of a local R. burneti bp strain, isolated from sheep, were studied in view of its eventual use for active immunoprophylaxis against ky-fever in animals. The investigation was performed in guinea-pigs with 2 series corpuscular antigens: first phase antigen produced from guinea pig spleens and second phase antigen produced from yolk sacs of hen embryos. Each preparation was tested in concentrations of 500, 250, 62 and 31 millions microbial cells per 1 cm3. It was established that the R. burneti bp strain possesses immunogenic complexes of I and II phase. The corpuscular antigens of the strain of the I phase are immunogenically more active than these of the II phase. Immunization of guinea pigs with first phase antigen stimulated the production of "early" and "late" antibodies and of complete immunity. Guinea pigs are fully resistant to 10(-6) infection doses of R. burneti following their subcutaneous immunization twice at an interval of 10 days with 1 cm3 of first phase antigen in a concentration of 62 million microbial cells per 1 cm3.