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Chapter 17 : The Evolution of Human Fungal Pathogens
Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
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This chapter focuses primarily on the subset of human pathogenic fungi. Even among this relatively small subset of organisms, there is extensive variation in phylogenetic ancestry, pathogenic strategies, ecology, prevalence, and outcome of infection. The major fungal pathogens constitute a diverse group of organisms. With the exception of Candida spp. and Malassezia furfur, all other pathogenic fungi discussed in this chapter are saprophytic. Pathogens can be classified as generalists or specialists depending on their host range. The chapter also focuses on broad areas of the macroevolution of fungal pathogenesis. In fungi, the two important genetic changes that result in microevolution are genetic rearrangements and point mutations. Macroevolution in terms of speciation has led to the development of multiple pathogenic fungal species. The chapter proposes different hypotheses and supporting data on the evolution and development of fungal pathogenesis. Though the specific mechanisms of evolution and development of virulence factors have not been elucidated, there are clear data implicating soil amoebae as a natural predator that may maintain virulence in the fungal habitat. Given increasing interest in this area, future studies will shed additional light on the evolution of fungal pathogenesis.
Fitch-Margoliash distance tree based on 23S-like rRNA sequences (adapted from reference 38 ). The phylogenetic tree demonstrates the taxonomic location of fungi within the kingdoms.
Fitch-Margoliash distance tree based on 16S-like rRNA sequences (adapted from reference 38 ). The phylogenetic tree demonstrates the interspersal of pathogenic and nonpathogenic fungi.
Scanning electron microscopy image of C. neoformans (small cells) with Acanthamoeba castellanii (large cell). This image demonstrates the interactions between the fungal cells and amoeba 30 min postincubation.
Fungal pathogens, disease, and virulence
C. neoformans virulence factors and their possible role in the environment