Many fungal infections, or mycoses, of humans and animals affect only the outer layers of skin, and although they are sometimes difficult to cure, they are not considered dangerous. Athlete's foot and ringworm are among the common superficial fungal infections. Fungal infections of the mucous membranes are caused primarily by Candida albicans (see candidiasis). It usually affects the mouth (see thrush) and the vaginal and anal regions.
The fungi that affect the deeper layers of skin and internal organs are capable of causing serious, often fatal illness. Sporotrichosis is an infection of farmers, horticulturists, and others who come into contact with plants or mud. The disease affects the skin and lymphatic system and, in rare cases, becomes disseminated. Blastomycosis is caused by a yeastlike fungus that reproduces by budding. The North American variety, caused by Blastomycosis dermatitidis, occurs more often in men and seems to be limited to the central and E United States and Canada. Wartlike lesions appear most often on the skin, sometimes spreading to the bones and other organs. The South American variety of blastomycosis is caused by B. brasiliensis. Chytridiomycosis, caused by Batrachochytrium dendrobatidis, is a deadly fungal skin infection in amphibians, which it kills by damaging to the animals' normally permeable skin, thus disrupting the transport of air and moisture.
Among the fungi that infect the deeper tissues is Coccidioides immitis, which causes coccidioidomycosis, sometimes called valley fever, a lung infection that is prevalent in the SW United States. Cryptococcosis is another fungus disease that may be localized in the lung or disseminated, especially to the central nervous system. It has a worldwide distribution, affecting men twice as often as women. The causative agent ( Cryptococcus neoformans ) has been isolated in pigeon excretions. Histoplasmosis, which is caused by spores of the fungal genus Histoplasma, is a severe infection that shows varied symptoms. In acute cases ulcers of the pharynx and enlargement of the liver and spleen are present. In other forms tubercularlike lesions of the lung occur. In its benign form no symptoms may be present.
Fungal infections sometimes follow the use of antibiotics, which kill nonpathogenic as well as pathogenic bacteria, thereby providing a free field in the body for fungal invasion. Opportunistic fungal infection occurs when a fungus enters a compromised host, as in the case of such diseases as AIDS. Treatment for fungal infections includes systemic antifungal agents, such as amphotericin B, fluconazole, and itraconazole, and agents usually used topically, such as clotrimazole (Lotrimin) and miconazole (Monistat).