Chapter 2 - Yeasts pathogenic for humans

Abstract

This chapter focuses on various pathogenic yeasts in humans. The principal yeasts pathogenic for humans are Candida albicans and Cryptococcus neoformans. Candida albicans is an asexual, diploid (possibly aneuploid), plemorphicfungus with an ascomycetous-type cell wall. This species is endogenous in the oral-, gastrointestinal-, or urinogenital tracts of humans and other warm blooded animals. The syndromes produced by Candida albicans are highly diversified including vulvovaginitis, dermatitis, cystitis, fever, myositis, hepatic disfunction, and mental confusion. These may occur singly or in combinations dependent upon the superficial, locally invasive, or deep nature of the infection. Cryptococcus neoformans, which is basidiomycetous yeast, includes two varieties that are often haploid when isolated from nature. Cryptococcus neoformans var. neoformans includes serotypes A, D, and AD. C.neoformans var. gatti includes serotypes B and C. Serotypes A and D are usually associated with soil enriched with pigeon droppings. Serotype A is most common in the U.S.A. and serotype D is reported mostly from Europe. Serotypes B and C seem confined to warm regions, particularly serotype B has been associated with the flowering of Eucalyptus camaldulensis. Cryptococcus neoformans most often primarily infects the lungs with mild symptoms. In stressed patients, pneumococcal-type pneumonia is not uncommon. Candida tropicalis is probably the third most important yeast pathogen of humans. Normally, this species does not produce germ tubes or chlamydoconidia, but elongated pseudohyphal cells may develop commonly in some strains in serum at 37°C. Candida tropicalis, like C. albicans, is diploid ascomycetous-type yeast, but it is commonly isolated from host-free habitats.