African histoplasmosis: a review

Abstract

African histoplasmosis caused by Histoplasma capsulatum var. duboisii is an important deep mycosis endemic in Central and West Africa and in the island of Madagascar. The disease is characterized by presence of granulomatous lesions in the skin, subcutaneous tissues and bones. Lungs and other internal organs are rarely involved. The natural reservoir of the etiological agent has only been recently discovered in a bat cave in Nigeria. The status of asymptomatic infection is not certain. Investigations on skin and serum reactivity have suggested frequent prevalence of asymptomatic infections due to H. capsulatum var. duboisii among the residents in the vicinity of the cave microfocus of the fungus. The exact portal of entry into the body is not known, but inhalation into the lungs and direct inoculation in the skin have been incriminated. Laboratory diagnosis is confirmed by in vitro conversion into large yeast forms (8-15 mum in diameter) and by the demonstration of these forms within giant cells of tissues of experimentally infected animals There are no major clean-cut physiological differences between the two varieties, viz. capsulatum and duboisii. The cell wall of H. capsulatum var duboisii contains a glucan with beta 1-4 linkages in addition to a galactomannan shared with H. capsulatum var. capsulatum. Like the var. capsulatum var. duboisii has marked proteinase and collagenase activities in both mycelial and yeast forms, suggesting a possible pathogenic role for these enzymes. Both varieties have a common exoantigen. The yeast form of H. capsulatum var. duboisii contains the antigen found in the serotype 1,4 of var. capsulatum. A monoclonal antibody test has been developed that can recognize some epitopes in H. capsulatum var. capsulatum but not in the var. duboisii. There is need to develop specific serological diagnosis for the disease. Also there should be greater international awareness about African histoplasmosis. Amphotericin B and several antimycotic azoles like ketoconazole, itraconazole and fluconazole have been successfully employed for treatment.