Evaluation of a specific double-diffusion technique in paracoccidioidomycosis diagnosis
Yarzábal, L.A.; de Cabral, N.A.; Santiago, A.R.
Acta Cientifica Venezolana 30(1): 93-97
1979
ISSN/ISBN: 0001-5504 PMID: 121904 Document Number: 140044
Double diffusion in gel (DDG) is the simplest and most practical test for the diagnosis of paracoccidioidomycosis. The most important limitation of this test is the eventual appearance of false-positive reactions when it is performed with crude antigens of Paracoccidioides brasiliensis. This risk can be reduced by the use of specific antigens of the causative agent or the identification of the antibodies produced by the host against these antigens. Using the 2nd alternative, the DDG test was modified with the objective of demonstrating the antibodies formed against the antigen E2, which are specific for P brasiliensis. The variation consists of reacting a rabbit immune serum against E2 with a crude antigen from the fungus and the human sera being studied; only those human sera which produce a precipitin band of immunological identity to that produced by the monospecific serum are considered positive. Based on this criterion, a comparative evaluation with the classical DDG test and immunoelectrophoresis was done using 130 sera: 45 from patients with paracoccidioidomycosis, 60 from patients with other mycoses and 25 from normal individuals. The sensitivity of the proposed technique was similar to that of the other 2 tests. The specificity was superior to that of the classical double diffusion test; no false positive reactions were observed. The procedure requires smaller quantities of antigen and sera than classical DDG. The postulated modification significantly reduces the risk of cross reactivity in the DDG test applied to the diagnosis of paracoccidioidomycosis without affecting the sensitivity of the test.