Dermatophytes: Fungi, Infections, and Classification

• Dermatophytes are fungi that infect skin, hair, and nails.
• These fungi use keratin as a nutrient source, allowing them to infect keratinized tissues.
• Dermatophytosis, also known as ringworm or tinea, is caused by dermatophytes.

Classification

• Dermatophytes are classified into the Trichophyton, Microsporum, and Epidermophyton genera.
• Trichophyton species infect skin, hair, and nails.
• Microsporum species primarily infect skin and hair.
• Epidermophyton species typically infect skin and nails.

Transmission

• Transmission happens through direct contact with infected individuals or animals.
• Indirect contact is possible via contaminated objects, including towels, clothing, and surfaces.
• Humidity, sweating, and minor skin injuries increase the risk of infection.

Pathogenesis

• Dermatophyte infection starts with fungal spore (arthroconidia) adherence to the skin surface.
• Germination occurs, followed by hyphal growth and invasion of the stratum corneum.
• Fungal enzymes like keratinases break down keratin.
• The host's immune response causes inflammation and clinical manifestations.

Clinical Manifestations

• Tinea capitis is a scalp infection, common in children, causing hair loss and scaling.
• Tinea corporis is a body infection, characterized by circular, raised, scaly lesions.
• Tinea cruris is a groin infection, more common in males, causing itching and discomfort.
• Tinea pedis is a foot infection (athlete's foot) that causes scaling, itching, and burning between the toes.
• Tinea unguium is a nail infection (onychomycosis) that causes thickening, discoloration, and deformation of the nails.

Diagnosis

• Clinical examination involves visual inspection of lesions.
• Microscopic examination uses KOH (potassium hydroxide) preparation of skin, hair, or nail scrapings to visualize fungal elements.
• Fungal culture uses Sabouraud's dextrose agar (SDA) to grow and identify dermatophytes.
• Wood's lamp examination uses ultraviolet light to detect certain Microsporum species (fluorescence).
• Dermatophyte test medium (DTM) is a selective medium that changes color in the presence of dermatophytes.

Treatment

• Topical antifungal medications include creams, lotions, or powders containing azoles (e.g., miconazole, clotrimazole), allylamines (e.g., terbinafine), or ciclopirox.
• Oral antifungal medications are used for widespread or severe infections, or when topical treatment fails; examples include terbinafine, itraconazole, and fluconazole.
• Nail infections often require prolonged oral therapy due to slow nail growth.

Prevention

• Practice good hygiene by regularly washing hands and body.
• Avoid sharing personal items like towels, clothing, and shoes.
• Keep skin dry and cool, especially in areas prone to infection.
• Wear protective footwear in public areas like gyms and swimming pools.
• Promptly treat infected individuals and animals to prevent further spread.