fungal virulence

Virulence or pathogenicity is a microbial trait expressed in a susceptible host and that trait allows the pathogen to cause damage to the host. In general fungi can be divided into two groups, those that are commensal and become an opportunistic infection, and endemics, which are those fungi that are acquired from the environment and have the ability to cause disease (Casadevall et al. 2003; Romani and Howard 1995; Rooney and Klein 2002). Commensal fungi are organisms such as Candida albicans that grow on human skin and do not usually cause any disease, except in rare cases of exposure to extremely virulent strains in hospitals or immune suppression that releases the fungus from host control. Endemic fungi are usually acquired from the environment by inhalation or dermal invasion. Mammals are exposed to fungal spores everyday, but don’t usually get sick. The innate immune system is capable of recognizing and destroying most fungi before any harm is done. Often, sickness results from exposure to toxins, rather than development of a persistent infection. However, when a mammal is exposed to a fungal pathogen such as Coccidioides spp., Histoplasma capsulatum, Cryptococcus neoformans, Paracoccidiodes brasilienses, Aspergillis fumigatus, Penicilium marneffi, Sporothrix schenkii, or Blastomyces dermatiditis, a more severe disease may develop. These fungal pathogens are not restricted to a single class or order; indeed, it appears that fungi have developed virulence in mammalian hosts, independently and multiple times.