Fungal Diseases

About fifty fungal species cause human disease, usually by one of three ma­jor mechanisms. First, some fungi cause an immune response, resulting in hypersensitivity (allergic) reactions to the fungi. (The fungi themselves thus act as antigens.) For example, several Aspergillus species can cause asthma and other allergic reactions. The second mechanism is found in fungal species producing poisons or mycotoxins. Aspsergillus flavus grows on im­properly stored grain and can produce aflatotoxins that cause tumors in birds and various other animals.

The third disease mechanism is infection. Mycoses (singular, mycosis) are fungal infections found in or on the body. Most mycoses are “nuisance” diseases, although some can be quite serious or even life-threatening. Many of the mycoses are caused by opportunistic organisms, organisms taking advantage of the patient whose defense mechanisms are down (such as per­sons suffering from AIDS [acquired immunodeficiency syndrome] ). Exam­ples of opportunistic mycoses include histoplasmosis (usually respiratory), cryptococcosis (affecting any organ, often the brain), coccidioidomycosis (of­ten respiratory), and candidiasis (the common yeast infection affecting any part of the body). (Candidiasis in the mouth and throat of newborns is called thrush.)

Superficial mycoses affecting the skin, scalp, hair, or nails are spread by contact with infected persons or contaminated objects. These common my­coses are generally self-limiting. Tinea is a categorical term used to describe fungal infections by their location, such as tinea capitis (head, also known as ringworm), tinea barbae (beard), tinea corporis (body), tinea cruris (gen­ital and anal areas, also known as jock itch), tinea pedis (foot, also known as athlete’s foot).

subcutaneous mycoses develop in wounds and often resemble ulcers or chancres. Sporotrichosis (caused by Sporothrix schenckii) is a common sub­cutaneous mycosis.

The systemic mycoses, which develop when a fungus invades the in­ternal organs (or systems), are extremely difficult to treat, particularly in im­munocompromised patients. Yeast, classified as a type of fungus, can cause infection of the urinary tract.

References

Madigan, Michael T., John M. Martinko, and Jack Parker. Brock Biology of Microor­ganisms, 9th ed. Upper Saddle River, NJ: Prentice Hall, 2000.

Thomas, Clayton L., ed. Taber’s Cyclopedic Medical Dictionary, 18th ed. Philadelphia, PA: F. A. Davis Company, 1997.