A Toxic Substance Associated with the Rickettsias of the Spotted Fever Group

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Abstract
Summary: A toxic substance was demonstrated in yolk sac cultures of ten strains of the spotted fever rickettsia which were selected according to their virulence for guinea pigs, tick-host species, or etiologic relationship to the various diseases of the spotted fever group. These strains included the agents of Rocky Mountain spotted fever, boutonneuse fever, South African tick bite fever and Indian tick typhus. Three variables are shown to affect the production of the toxic factor in yolk sac cultures of R. rickettsii. These variables were (a) incubation of infected eggs after death of the embryo, (b) dose of inoculum used to initiate the egg cultures, and (c) the length of the time of survival of the embryo after inoculation. The toxin of R. rickettsii was found to be specifically neutralized by serums of spotted fever convalescent individuals or experimental animals. It was also found to be neutralized by serums of human beings or guinea pigs following their injection with spotted fever tick vaccine.