Astrakhan fever rickettsiae: antigenic and genotypic analysis of isolates obtained from human and Rhipicephalus pumilio ticks.

Two spotted fever group rickettsia strains, A-108 and A-167, were isolated from the hemolymph of Rhipicephalus pumilio ticks collected in the Astrakhan region of Russia, which is area endemic for Astrakhan fever. These tick isolates were compared with a strain isolated from a patient suffering from Astrakhan fever and with reference spotted fever group rickettsiae strains. New tick isolates and the human strain were identical in their serologic, antigenic, and genetic characteristics by several methods: microimmunofluorescence, protein gel electrophoresis with immunoblotting, polymerase chain reaction followed by restriction endonuclease fragment length polymorphism analysis, and pulsed-field gel electrophoresis (PFGE). Astrakhan fever rickettsiae were found to be serologically and antigenically similar to Israeli spotted fever rickettsiae. Both of them probably belong to a single Rickettsia conorii pathotype complex. Only PFGE pattern analysis could clearly discriminate Astrakhan fever rickettsiae from other isolates.