Pathogenic fungi are microorganisms that can cause disease in humans. While many fungi exist in the environment, these fungi are widespread, found in soil, plants, and even on human skin, typically without causing harm. However, under specific conditions, they can invade host tissues and overcome the body’s defenses, leading to various types of infections.
Common Types of Fungal Infections
Fungal infections are categorized based on the body parts they affect. Superficial or cutaneous infections are the most common, impacting the outer layers of the skin, hair, and nails. Examples include athlete’s foot (tinea pedis), which causes itching and peeling between the toes, and ringworm (tinea corporis), which can appear as a red, scaly rash on the body. Nail infections, or onychomycosis, result in discolored and thickened nails.
Mucocutaneous infections involve mucous membranes, such as those in the mouth, throat, or vagina. Candidiasis, often caused by Candida albicans, is a common example, leading to oral thrush with white patches or vaginal yeast infections characterized by itching and discharge. Candida species are naturally present on the body but can overgrow under certain circumstances.
Subcutaneous infections penetrate deeper into the skin and underlying tissues. These are more prevalent in tropical and subtropical regions and typically occur when fungi are introduced through skin trauma. Sporotrichosis is caused by Sporothrix schenkii and can result in lesions and swelling at the site of infection. Other examples include chromoblastomycosis and mycetoma, which can cause chronic skin lesions and tissue damage.
Systemic or deep fungal infections affect internal organs, often originating in the lungs and spreading throughout the body. These infections can be caused by fungi like Histoplasma, Coccidioides, and Blastomyces, which are typically inhaled from the environment. Aspergillosis, caused by Aspergillus mold, can lead to lung infections and disseminate to other organs, including the brain, kidneys, or heart.
Who Is at Risk and How Fungi Spread
Environmental exposure is common, with fungal spores present in air, soil, and decaying organic matter. Inhaling these microscopic spores can lead to respiratory infections, especially for systemic mycoses. Direct contact with an infected person, animal, or contaminated surfaces like gym mats or towels can also spread certain superficial infections, such as ringworm or athlete’s foot.
While exposure is common, not everyone develops an infection. Individuals with weakened immune systems face a higher risk of fungal diseases, including those with HIV/AIDS, cancer (and its treatments like chemotherapy), or who use immunosuppressant medications for autoimmune diseases or organ transplants. Other factors that increase susceptibility include:
Diabetes
Poor circulation
Prolonged antibiotic use, which can disrupt the body’s natural microbial balance
Occupations that involve extensive contact with soil
Diagnosing and Treating Fungal Infections
Diagnosing fungal infections involves several approaches, depending on the suspected type. A physical examination is often the first step, especially for superficial infections, where visible symptoms like rashes, itching, or scaling can provide initial clues. For skin, hair, or nail infections, a healthcare professional may take scrapings, clippings, or samples for microscopic examination, often using a potassium hydroxide (KOH) preparation to visualize fungal elements. Fungal cultures can also be performed to grow and identify the specific pathogen, though this can take several days.
For deeper or systemic infections, diagnosis may involve blood tests to detect fungal antigens or antibodies, or imaging studies like X-rays to assess organ involvement, particularly in the lungs. In some cases, a biopsy (tissue sample) might be necessary for accurate identification. Prompt and accurate diagnosis is important for effective treatment, particularly in individuals with compromised immune systems.
Treatment for fungal infections primarily involves antifungal medications, which work by either killing the fungus or inhibiting its growth. These medications are available in various forms: topical creams, ointments, gels, or sprays for skin and nail infections; oral pills or liquids for more widespread or persistent conditions; and intravenous (IV) formulations for severe systemic infections. The duration of treatment varies considerably, from a few weeks for mild skin infections to several months or even years for certain nail or deep-seated infections. Common antifungal drug classes include azoles (e.g., fluconazole) and echinocandins (e.g., micafungin), with newer, less toxic options now available for serious cases.
Preventive measures can help reduce the risk of fungal infections. Maintaining good personal hygiene, such as keeping skin clean and thoroughly dry, especially in folds and between toes, is beneficial as fungi thrive in warm, damp environments. Wearing clean, breathable clothing and footwear, and avoiding walking barefoot in communal areas like public showers or locker rooms, can also help prevent spread. Not sharing personal items like towels or nail clippers is also advised to minimize transmission.