Fungi: Pathogenic fungi are uncommon in humans. Most are dermatophytes, infecting the skin, hair or nails. They feed by extracellular digestion and reproduce asexually by spore production. Candidates should be able to describe the course of infection and the signs and symptoms of athlete’s foot; to relate its effects to the pathogen’s method of feeding.

The fungi are saprophytes, they feed on dead material and some have become parasites (they don’t wait for their food source to die!).

A few species of fungi have adapted to feed upon keratin in the human skin. They secrete enzymes and digest the dead skin cells extracellularly. The products of digestion are then absorbed by diffusion and active transport. Two related species are common, these are Tinea pedis, causing Athletes Foot, and Tinea capitis which causes Ringworm. Both species are highly infective but require a damp skin surface on which to germinate successfully. They produce hyphae which penetrate through the epidermal layer of the skin and this causes damage and secondary bacterial infections can occur. The treatment is by use of a fungicidal powder or by use of an antibiotic called griseofulvin taken orally.

A yeast like fungus called Candida albicans causes Thrush. This is an infection which may occur in the mouth, vagina or intestines. The fungus is seen as white fluffy patches on the infected surfaces and the irritation causes intense itchiness. Secondary infections with bacteria are common. Treatment is by use of a fungicide usually applied as a lotion, for oral infections, pessaries for vaginal infection. The drug amphotericin can be used for intestinal infection. Although largely regarded as a minor problem in Britain, the Americans take it very seriously and suspect that progressive invasion through the intestines causes serious debilitating effects on the host.