[Study of serologic cross reactions between the antigens of Paracoccidioides brasiliensis and Histoplasma capsulatum].

A comparative study of serologic cross-reactions between histoplasmosis and paracoccidioidomycosis was carried out using complement fixation (CF) and agar gel immunodiffusion (ID) tests. Sera from 77 patients with paracoccidioidomycosis, 38 with histoplasmosis and 50 healthy individuals were studied. The Pan American Health Organization microtiter CF test and the Hupper ID technique were employed. The antigens were prepared by the method of Ajello as modified by Negroni. Paracoccidioidin CF test was positive in all patients with paracoccidioidomycosis; 29 of these (37%) presented serologic cross-reaction with histoplasmin. Histoplasmin CF test was positive in all but one of the patients with histoplasmosis and only 4 of them (10%) showed cross-reaction with paracoccidioidin. Positive reactions with the ID test were registered in 74/77 cases of paracoccidiodomycosis, with only one case of cross-reaction (1,3%). The result for the ID test was positive in all but one of the cases of histoplasmosis, with only one cross-reaction with paracoccidiodin (2,7%). The ID test seemed to be much more specific although it could be less sensitive. It was also easier to perform and less expensive than the CF test. Nevertheless the authors urge that the CF test also be carried out whenever posible, since the information obtained is likely to be of more value in follow-up and control of patients.