There are 100,000 known fungi and only few infect humans mostly opportunistically. Only few are involved in human diseases because most fungi are destroyed by cell-mediated immune responses however, humoral immunity plays little or no role.
Predisposing factors for fungal infections include
Corticosteroid administration, acquired or congenital immunodeficiency states, defects in neutrophillic and macrophage functions. Fungal infections are divided into superficial and deep fungal infections (mycosis).
Normally found in mouth, skin and gastrointestinal tracts. It is the most common fungal infection mostly caused by (C. albicans). It affects locally the skin, nail and mucous membranes and it grows best in warm, moist surface and cause vaginitis, diaper rash & oral thrush.
Systemic candidiasis widespread in persons with depressed immune responses including lymphohemopiotic malignancy, immunosuppressive therapies and broad-spectrum antibiotic usage as well as patients with dialysis, cardiac surgery, IV drug abusers.
Cryptococcos neoformans is encapsulated yeast. It causes menigioencephalitis in normal individuals but more frequently in patients with AIDS, leukemias, lymphomas, SLE, Hodgkin’s lymphomas and transplant recipients and those on steroid therapy.
Aspargillus is a ubiquitous mold that causes allergies in otherwise healthy persons and serious sinusitis, pneumonia and fungemia in neutropenic persons. Aspargillus form fruiting bodies.
The causative organism H. capsulatum is recovered from dust particles of soil, bird or bat droppings contain small spores (micro conidia). Histoplasmosis and Coccidiomycosis resemble pulmonary tuberculosis and both are caused by fungi that are thermally dimorphic (hyphae and yeast forms)