Antigenic relations of Rickettsia prowazekii and Rickettsia canada, established in the study of sera of patients with Brill's disease.

Sera of patients with Brill's disease and of healthy persons with spotted fever in their past history were examined in the complement fixation reaction (CFR) to determine antigenic relations between R. prowazekii and R. canada. R. canada was found to have common antigenic determinants with R. prowazekii and R. mooseri. However, the antigenic determinants of R. canada differed from those of the mentioned rickettsiae. The titres of complement-fixing antibodies in the sera of patients with Brill's disease with the antigen of R. mooseri were lower than the titres with the homologous antigen within the range of 1-2 twofold dilutions of the serum. However, the oscillations of the titres with the antigen of R. canada in the study of the same sera were expressed in 1-5 twofold dilutions. In serological identification of canada rickettsiosis, antigens of rickettsiae of the spotted fever group should invariably be included in the investigation of the sera.