Immunoassay Developed for Histoplasmosis Diagnosis

The enzyme-linked immunosorbent assay (ELISA) detects antibodies to Histoplasma capsulatum, the causative agent of histoplasmosis, using metaperiodate treated purified histoplasmin (ptHMIN), the specific antigen of this fungus.

To evaluate the ELISA test clinical serum samples were selected randomly from the Immunodiagnostic Section Serum Bank, Laboratory of Mycology, Institute of Clinical Research Evandro Chagas, (Fiocruz; Rio de Janeiro, Brazil). Forty-four sera samples were tested from homologous histoplasmosis and 35 sera samples from other cases of mycoses. These included seven with paraccocidioidomycosis; eight for each of the following: aspergillosis sporotrichosis, and cryptococcosis cases, and four from coccidioidomycosis patients. Additionally, 36 negative control sera from healthy donors were collected and tested.

The results of the assay showed that the optical densities (ODs) were significantly higher in sera from 44 patients with histoplasmosis than in heterologous-infected samples evaluated. Differences in the means and comparisons of parameters indicate that the test effectively discriminates between negative and positive samples. The distribution of OD values varied in the clinical groups, but no statistical differences were found between them. The OD values are an indication of antibody levels in the patients' sera.

The overall test specificity was 96%, with sensitivities of 100% in acute disease, 90% in chronic disease, 86% in disseminated disease co-infected with Human Immunodeficiency Virus (HIV), 89% in disseminated infection in individuals without HIV infection, and 100% in mediastinal histoplasmosis. The authors of the study concluded that the high specificities, sensitivities, and simplicity of the ELISA support further development of a deglycosylated HMIN ELISA for clinical use and for monitoring the humoral immune response during therapy in patients with chronic and disseminated histoplasmosis.

Histoplasmosis is a disease caused when airborne spores of the fungus H. capsulatum are inhaled into the lungs, the primary infection site. This microscopic fungus, which is found throughout the world in river valleys and soil where bird or bat droppings accumulate, is released into the air when soil is disturbed by plowing fields, sweeping chicken coops, or digging holes. The clinical disease generally ranges from mild influenza-like illnesses to progressive, disseminated disease, which manifests mostly in immunocompromised individuals. The study was published on line on January 4, 2010, in the open access journal Microbiology Research.

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Institute of Clinical Research Evandro Chagas