A Case of Tinea Corporis Caused by Trichophyton benhamiae var. luteum from a Degu and Evolution of the Pathogen’s Taxonomy

Background: Trichophyton benhamiae, an anthropophilic dermatophyte, can cause dermatophytosis in humans and animals with rising zoonotic infections through pets, primarily in Europe. Dermatophytosis from T. benhamiae is often misdiagnosed due to its inflammatory symptoms. We report a case of tinea corporis from T. benhamiae var. luteum in a Japanese woman, contracted from pet Czech degus. Case: The 40-year-old patient developed neck papules resembling acne. Initial treatment with topical antibiotics and steroids exacerbated the rash. Fungal elements were not detected by direct potassium hydroxide examination. Skin biopsy confirmed fungal elements in the stratum corneum and hair follicles, and tinea corporis was diagnosed. Oral terbinafine 125 mg was initiated without topical agents. Erythematous papules appeared on her limbs, determined as a trichophytid reaction. After two months, her skin improved significantly. Fungal culture identified T. benhamiae var. luteum colonies with a yellowish hue. Mating tests classified the strain as Americano-European race (−) with MAT1-1 genotype. This was diagnosed as tinea corporis from T. benhamiae var. luteum, likely transmitted from pet Czech degus. Conclusions: The incidence rate of pet-transmitted cutaneous fungal infections may increase in Japan with the trend to keep exotic pets. Dermatologists must recognize dermatophytosis clinical features from anthropophilic dermatophytes to prevent misdiagnosis and understand evolving nomenclature and pathogenesis.