Figure. Pictures of immunofluorescence assay performed on serum specimens with proven Rickettsia conorii (A), R. felis (B), or R. typhi (C) infection showing cross-reactive antibodies. Antigens tested were R. conorii (column 1), R. felis (column 2), and R. typhi (column 3). The serum with R. conorii infection reacts with R. conorii and R. felis antigens but not with R. typhi (A). Conversely, the serum with R. typhi infection reacts with R. typhi and R. felis but not with R. conorii (C). Finally, the serum with R. felis infection reacts with R. felis, R. conorii, and R. typhi.