ABSTRACT
The typhus complex classically contained only the two species of the Rickettsieae transmitted by insects, but may include a third member associated with ticks. Those two species are Rickettsia typhi and prowazekii. A possible third member of the typhus complex, Rickettsia canada, naturally infecting ticks in North America was discovered in 1967. Antigenically and biologically R. typhi is more closely related to R. prowazekii than to R. Canada. On the molecular level, the DNA of the typhus rickettsiae and R. Canada contain identical percentages of guanine + cytosine. Rickettsia prowazekii would seem to be removed from any obligate association with ticks. The first reports of possible infection of domestic animals with R. prowazekii are those of Giroud and his colleagues in Africa, who based their conclusions on results of serological tests of questionable validity. Using type-specific agglutinating antigen, the antibody was identified unequivocally as R. typhi, not R. prowazekii.
