Fungi

Fungi are all round us, living in air, soil, on plants and in water.

Fungi Are Part of Our Everyday Lives

Fungi such as yeasts are used for bread making, brewing of beer and other species are used in wine and cheese making. We eat fungi directly as marmite, mushrooms and Quorn. Fungi are in our homes as mould and mildew.

Many fungi reproduce and disperse through microscopic spores that become airborne and are inhaled or take advantage of small abrasions on the skin.  As a result, fungal infections often start in the lungs (aspergillosis, fungal hypersensitivity in asthmatics) or on the skin (ringworm and athlete’s foot).

Fungi are eukaryotes and share similar cell structures and metabolism to human cells, although fungi uniquely have a fungal cell wall. This limits the available targets for antifungal drug action, and some antifungal drugs may cause liver toxicity or drug interactions e.g. with Warfarin. Fungi can be difficult to kill and eradicate and may require long term treatment, typically fungal nail infections.

Fungal Infections in the Mouth

In dentistry the most common fungal infection is due to Candida spp, a yeast like fungi. Symptoms vary, from asymptomatic to a sore and painful mouth with a burning sensation and altered taste. Oropharyngeal candidiasis can impair speech, eating and quality of life.

There are four main types of Oropharyngeal candidiasis:

Pseudomembranous (Thrush)

Consisting of white, curd-like discrete plaques on an erythematous (red) background which is exposed after removal of the plaque. Found on the buccal mucosa, throat, tongue, or gingivae.

Erythematous

Consisting of smooth red patches on the hard or soft palate, dorsum of tongue, or buccal mucosa (associated with steroid inhaler or antibiotic use).

Chronic Hyperplastic Candidiasis

Consisting of white, firmly adherent patches or plaques that cannot be removed. Usually bilaterally distributed on the buccal mucosa at the angle of the mouth or less commonly on the tongue or palate. These lesions are often excised surgically if they do not respond to antifungal treatment as they show potential for malignant change in a small percentage of people.

Denture-Induced Stomatitis

Presented as either a smooth or a granular erythema confined to the denture-bearing area of the hard palate.

Risk Factors for Candidiasis

Candida species are commensals in the mouth and are part of the oral flora. Candida is found in the mouth of 18% to 60% of healthy people, the percentage increasing with age and denture wear.

Candida associated denture stomatitis occurs in approximately 65% of denture wearers. Most candida infections are endogenous infections, the infection being caused by the candida that normally colonises the patient. The candida yeasts adhere to the epithelial cells lining the mouth.

During infections, the yeasts produce an array of virulence factors and pseudo-hyphae (elongated cell projections) that penetrate and grow through the underlying mucosa, triggering an inflammatory response and cell damage.

Oropharyngeal candidiasis is an opportunistic infection and can follow the use of broad spectrum antibiotics that disrupt the oral flora or local immunosuppression with inhaled steroid or systemic steroids.

Oropharyngeal candidiasis affects up to 60% of people with malignancies during periods of immunosuppression. Other risk factors for candida infections include diabetes, dry mouth, iron, folate or B12 deficiency, HIV, smoking and high carbohydrate intake.

Oropharyngeal candidiasis is the most common oral manifestation of untreated HIV infection.   

Treatment of Oral Candidiasis

Candidiasis responds to treatment with antifungals but for effective treatment the underlying cause should also be treated, or risk factors such as smoking stopped, and dentures removed at night.

The most commonly used topical antifungal drugs for treating oral candidiasis are miconazole and nystatin or systemic drugs such as fluconazole or itraconazole.

In immunosuppressed people or poorly controlled diabetics, candidiasis relapse rates can be high following treatment and some patients may require long term intermittent prophylaxis with antifungals.