A search for the epidemic typhus agent in Ethiopian ticks

The presence of antibodies to Rickettsia prowazeki in domestic animals from several parts of Africa, and the isolation of this rickettsia from the blood of goats and sheep and from ticks off cattle or camels in Ethiopia, led to the hypothesis that R. prowazeki in nature may occur in an extrahuman cycle involving ticks and domestic animals. This study attempted to recover R. prowazeki from 2 624 ticks (4 genera, 10 species) collected in central and southern Ethiopia. The ticks were examined by the haemolymph test and by the injection of tissues into guineapigs. No strains of typhus rickettsia were received and there was no serologic evidence suggesting the presence of this agent in any of the ticks examined. One Amblyomma cohaerens contained an organism that reacted specifically with fluorescing antibodies against R. prowazeki; attempts to isolate and identify this agent failed. Fifty-seven (2.2%) Amblyomma ticks (26 A. gemma, 17 A. variegatum, 14 A. cohaerens) were infected with rickettsiae of the spotted fever group, and probably represented R. conori or closely related rickettsial agents.