Evolution of Parasitism and Pathogenic Adaptations in Certain Medically Important Fungi

Abstract

Fungi are eukaryotes designated as a separate kingdom because of their unique characteristics different from both animals and plants. Fungi are mainly classified into two major types as “saprobes” and “parasites” depending on their type of nutrition and existence. It is postulated that the present-day parasites also once existed as saprophytes in the soil. It is also curious to find the reasons on what early events could have been responsible for the evolution of the saprobes into human parasites? During this process of evolution, some of the anthropophilic organisms have totally lost all their soil-inhabiting traits and the ability for saprophytic survival, while few others have successfully retained their ability to survive in two different ecological niches (soil and animal/human host). The various possible reasons, such as predation, antagonism, and other factors contributing to the emergence of parasitic adaptations, are discussed using examples of dermatophytes, Cryptococcus neoformans, and Histoplasma capsulatum.