Microsporum

Microsporum is a genus of keratinophilic fungi in the family Arthrodermataceae, order Onygenales, class Eurotiomycetes, within the phylum Ascomycota. They are dermatophytes that cause infections of keratinized tissues in humans and animals. Together with Trichophyton and Epidermophyton, Microsporum is one of the principal groups responsible for cutaneous and occasionally hair infections.

Morphology and identification are based on culture characteristics and microscopic features. In culture, Microsporum species typically produce abundant, thick-walled macroconidia that are large and spindle- or lemon-shaped with rough walls. Microconidia, when present, are usually small and sparse. These macroconidia are a key distinguishing feature from other dermatophyte genera.

Ecology and epidemiology vary by species. Some, like Microsporum canis, are strongly associated with animals (especially cats and dogs) and are a common source of zoonotic infections in humans. Others, such as Microsporum gypseum, are geophilic and more commonly acquired from soil. Microsporum audouinii is primarily associated with human-to-human transmission. Transmission occurs through direct contact with an infected animal or person, or via contaminated objects and environment.

Clinical disease commonly includes tinea capitis, corporis, faciei, and occasionally other sites, with presentations influenced by the species involved and the host’s age. Tinea capitis is a notable concern in children when M. canis or M. audouinii are involved.

Diagnosis relies on direct examination of skin, hair, or nails with potassium hydroxide or fluorescence methods, and culture on Sabouraud dextrose agar. Identification is aided by colony morphology and microscopic features; molecular methods may be used for confirmation.

Treatment includes topical antifungals for localized disease and systemic antifungals (such as terbinafine, itraconazole, or fluconazole) for scalp or extensive infections. Managing animal reservoirs and environmental decontamination help prevent reinfection.