COMPARATIVE ANTIGENIC ANALYSIS OF SPOTTED-FEVER GROUP RICKETTSIAE FROM ISRAEL AND OTHER CLOSELY-RELATED ORGANISMS

Spotted fever rickettsiosis in Israel has been considered as possibly somewhat more severe than boutonneuse fever, from which it also differ s in having a very low proportion of cases with a tick-inoculation sit e eschar. This investigation was undertaken to determine whether the I sraeli spotted fever group (SFG) rickettsiae differed sufficiently fro m Rickettsia conorii to be considered as a distinct species. Strains o f Rickettsia conorii from Morocco and South Africa, four SFG rickettsi al isolates from Israel, one from Russia, and one from Zimbabwe were c ompared by microimmunofluorescence serotyping, Western immunoblotting, monoclonal antibody reactivity, and polymerase chain reaction amplifi cation of the repeat domain of the rickettsial outer membrane protein A (rOmpA). All are strains and isolates of R. conorii, yet there is co nsiderable molecular and antigenic diversity of both rOmpA and rickett sial outer membrane protein B (rOmpB) among them. The rOmpA gene of th e Israeli isolates and the Astrakhan strain from Russia is estimated t o encode 15 rOmpA repeat units as compared with 10 for the South Afric an strain and six for the strains from Morocco and Zimbabwe. The Israe li SFG rickettsial strains appear to be R. conorii, a species with sub stantial antigenic and genetic diversity. The Israeli strains appear t o fall within the limit previously described for the genetic and antig enic diversity of R. conorii.