Deep fungal infections in tropical countries

Abstract

Deep mycoses are diseases that require knowledge of numerous medical specialties. According to modern concepts, deep mycoses are considered under two aspects: subcutaneous and systemic mycosis. Subcutaneous mycoses are characterized by a heterogeneous group of infections that often result from direct penetration of the fungus into the skin through trauma; and they spread by local tissue invasion in the inoculation area. The disease usually remains localized, slowly spreads to adjacent tissue, and eventually to lymphatic; or, more rarely, hematogenous dissemination is observed. A variety of clinical presentation is frequent, leading to a broad range of differential diagnoses. Chromomycosis, pheohyphomycosis, sporotrichosis, entomophthoramycosis, lobomycosis, and rhinosporidiosis belong to the group of the subcutaneous mycoses. Systemic mycosis consists of infections caused by truly pathogenic fungi and also those produced by fungi with small intrinsic pathogenicity, that is, enhanced by immunocompromised hosts, leading to the disease. In tropical regions, it is the first condition that leads to specific interest, whereas subcutaneous mycosis is found worldwide. The true systemic mycoses are produced in normal individuals when a minimal inoculated particle penetrates into the body. In the majority of cases, the respiratory tract may be the first site of entry, leading to initial lung infection; fungi then spread by hematogenous or eventually lymphatic vessels to other organs, including the skin. These diseases have a restricted geographic distribution due to the limited geographic occurrence of the etiologic agents. The majority of patients are represented by adult men as a consequence of prolonged exposure to fungi due to professional reasons. Apparently, black individuals show a higher risk of developing disseminated forms. The racial influence seems to have existed among Japanese immigrants in Brazil, who developed severe disseminated forms of paracoccidioidomycosis. Obviously, the direct contact with the land favors the opportunity to acquire fungal disease, justifying its higher frequency among rural peasants. After penetrating the human body, fungi usually arouse an adequate defensive response; these are the so-called infections without disease that occur in paracoccidioidomycosis, coccidioidomycosis, histoplasmosis, and cryptococcosis. Under these circumstances, the infection may be totally silent, or with discrete clinical symptoms, such as fever, with or without erythema nodosum; infectious state is detected only by positive intradermal tests utilizing involved fungal antigens. Epidemiological inquiries dealing with these intradermal tests show variable positive results in different regions, where they are performed according to fungi distribution; the percentage of positive results of these tests in populations demonstrate a direct relationship to the occurrence of the disease in the studied area. The association of these fungal diseases to other morbid processes, either infectious or carcinogenic, is occasionally cited. For example, cryptococcosis is sometimes associated with lymphomas, paracoccidioidomycosis, and pulmonary tuberculosis. Another possibility concerning systemic mycosis is the reactivation of a quiescent fungal focus in individuals living in endemic areas who acquired the silent infection, as demonstrated by positive response to intradermal tests. It is interesting to observe the development of the disease in these individuals after many years, due to multiple reasons that lead to an impaired immune response (aging, immunosupressant drugs, concomitant diseases). This event may happen many years after exposure to fungi, when the patient is no longer living in the endemic area, or is living in a country where the disease does not occur, making the diagnosis extremely difficult. This condition is the socalled imported pathology.