Fungal infections

Fungi are microorganisms that include yeasts and moulds.  Most fungi are harmless to humans, and some are quite beneficial.  Some species, however, are pathogenic to humans.¹  Common infections caused by fungi include:

• athlete’s foot
• jock itch
• vaginal yeast infections
• oral thrush
• ringworm

Fungal infections can be classified according to the general location of the infection:

Superficial or subcutaneous: infections which affect the outermost layer of skin or mucosal linings.  (E.g. vaginal thrush or oral thrush.)
Systemic: infections which widely disseminated throughout the body. (E.g. cryptococcal meningitis). These fungal infections most commonly occur in patients whose physical and / or immune defence systems have been weakened by disease or medical treatments (e.g. antibiotic treatment, immunosuppressant therapy).²

Origins of fungal infection

Fungal infections can be acquired by many routes.  Disease may result when fungal organisms that normally grow harmlessly in the body or on its surface are given opportunity to multiply and invade tissues¹, this is known as endogenous infection.

Contact with fungi from the environment is another source of infection.  Infections acquired from the environment are termed exogenous.  Some fungal infections can be transmitted from one person to another by superficial contact involving skin or mucous membranes, but most fungal infections are not contagious.²

Exogenous sources of infection

Infection can be acquired via the respiratory tract where fungal spores are inhaled and overwhelm the body’s defences.²  Fungal infection may also result when fragments of fungi or spores are introduced through breaks in the skin (e.g. when an intravenous catheter is used in a hospitalized patient).¹

Endogenous sources of infection

Many different types of microorganisms (microflora), including some fungi, grow inside the healthy body and on its surface.  Areas where fungi commonly colonize include the skin and the mucous membranes lining the upper respiratory tract, mouth, lower gastrointestinal tract, and female genital tract.  Colonization by the microflora is normally harmless to the host. However, disease can result when the balance of the microflora is upset.¹

References:
1. Beers MH, editor. The Merck Manual – Second Home Edition (online source). New Jersey: Merck Research Loboratories; 2005 (cited 2005 Sept 21).
2. Glynn E, Evans V, & Gentles JC. Essentials of Medical Mycology Churchill Livingstone, NY. 1985. P9-10.