Dermatophytosis in Iran: a sharp increase in cases caused by Trichophyton mentagrophytes var. indotineae

Abstract

Dermatophytosis is a common skin infection worldwide. In recent years, Trichophyton mentagrophytes var. indotineae has rapidly emerged as a leading cause of recalcitrant dermatophytosis. Iran shows high genetic diversity within the T. mentagrophytes complex, suggesting local emergence of new genotypes, yet nationwide data remain limited. We performed a one-year multicentre, hospital-based survey of referred cases (September 2023-September 2024) in nine provinces of Iran to describe the current epidemiology of dermatophytosis and to analyse mutations in the squalene epoxidase (SQLE) gene associated with terbinafine (TRB) resistance. Clinical samples were obtained from 2211 patients with suspected dermatophytosis. Dermatophytes were recovered from 1568 samples (71). Species-specific PCR identified T. mentagrophytes var. indotineae in 1191 cases (76), confirming it as the dominant agent across all clinical forms, age groups and provinces. The remaining isolates comprised other dermatophytes, mainly other members of the T. mentagrophytes complex, T. tonsurans and Microsporum canis. Trichophyton mentagrophytes var. indotineae caused most cases of tinea cruris, tinea corporis, mixed infections and generalised dermatophytosis. It also accounted for 59 of tinea unguium and 37 of tinea capitis cases. No significant sex bias was observed and most patients were 20-49 years old. The data did not indicate recent introduction of the infection from outside Iran, supporting ongoing local transmission. SQLE sequencing of 410 isolates revealed resistance-associated mutations in 45 of strains, mainly F397L (72) and L393S (28), with the highest frequencies in southern provinces. ITS sequencing of a subset of isolates confirmed their identity as T. indotineae and revealed two ITS genotypes, including a dominant genotype VIII and a new sub-genotype XXIX. These findings show that T. indotineae is now the dominant dermatophyte in Iran and carries a substantial burden of SQLE mutations, highlighting the urgent need for continued molecular surveillance and antifungal stewardship.