Immunocytochemical Identification of Rochalimaea henselae in Bacillary (Epithelioid) Angiomatosis, Parenchymal Bacillary Peliosis, and Persistent Fever with Bacteremia

&NA; We report the immunocytochemical identification of Rochalimaea henselae, a newly recognized fastidious, Gram‐negative, Warthin‐Starry‐positive organism, as the common pathogen in bacillary angiomatosis (BA), bacillary peliosis (BP) of the liver and spleen, and persistent fever with bacteremia in immunocompromised patients. Immunogenic proteins of the R. henselae strain isolated from the blood of a febrile immunocompromised patient with BP of the liver were used to produce primary immune serum in rabbits. Using immunocytochemical procedures, the polyclonal antiserum reacted strongly not only with the immunizing strain of the bacteria, but also with other blood isolates of R. henselae (five cases) from both immunocompromised and immunocompetent patients and with the organisms present in the tissue lesions of cutaneous BA (five cases) and BP of the liver (two cases) and spleen (one case). The blood isolates and BA and BP tissue samples were obtained from widely separated geographic areas. The antiserum was weakly crossreactive with cultures of Rochalimaea quintana, an organism closely related to R. henselae, but this reactivity was eliminated by specific adsorption. The antiserum did not cross‐react with the Warthin‐Starry‐positive organisms associated with cat scratch disease (Afipia felis), syphilis (Treponema pallidum), Lyme disease (Borrelia burgdorferi) or chronic active gastritis (Helicobacter pylori). Likewise, the antiserum did not identify organisms in eight cases of Kaposi's sarcoma, a disorder of immunocompromised patients that is clinically similar to BA. Further studies are needed to determine the prevalence of this newly recognized organism as well as its possible involvement in other angioproliferative diseases.