Medical significance of fungi

MEDICAL SIGNIFICANCE OF FUNGI

Fungi represent a significant group of pathogens capable of causing a range of diseases in humans under the right set of conditions. Although the majority of fungi appear to be harmless to humans it is worth bearing in mind that a normally non-pathogenic fungus can cause a clinically relevant problem if the immune system is suppressed as a result of therapy (e.g. for receipt of organ transplant) or disease (e.g. cancer). In a case of profound immune-compromise a wide range of fungi can present as capable of inducing disease.

The most common fungal pathogens of humans can be divided into three broad classes: yeasts, moulds and dermatophytes. The yeast C. albicans is the most frequently encountered human fungal pathogen, being responsible for a wide range of superficial and systemic infections. The superficial infections include oropharyngeal and genital conditions, the former occurs predominantly in HIV-positive individuals, geriatric patients and premature infants and may arise when a weakened or immature immune system is present. Genital candidosis is very common and approximately 75% of women are affected by vulvovaginal candidosis (VVC) during their life with a further 5–12% suffering from recurring bouts of infection over a prolonged period of time.

The mould Aspergillus fumigatus is the dominant fungal pulmonary pathogen of humans and generally presents as a problem in those with pre-existing lung disease or damage. In addition to pulmonary infection other sites may be affected including the brain, kidneys and sinuses depending upon the level of immunocompromise of the individual. Groups particularly susceptible to colonization by Aspergillus species include those with cavities due to tuberculosis, patients affected with asthma or cystic fibrosis and those with profound immunosuppression due to leukaemia (neutropenia). Aspergillosis presents as a serious problem in patients immunosuppressed in advance of organ transplantation.

Dermatophyte is the term applied to a range of fungi capable of colonizing the skin, nails or hair. The principal dermatophytic fungi are Trichophyton, Microsporum and Epidermophyton species. The most commonly encountered dermatophytic infections are athlete’s foot (infection of the foot) and ringworm (fungal infection of the scalp or skin).