Scratching the surface: The rise of antifungal-resistant dermatophytes

Dermatophytosis (also called ringworm or tinea infection) is a common, contagious superficial infection of the skin, hair, or nails caused by dermatophyte molds. Historically, clinicians have considered dermatophytosis as a mild, easy-to-treat condition; however, the epidemiology of dermatophytosis has changed dramatically in the past decade because of the emergence of dermatophyte strains causing increasingly severe and difficult-to-treat infections. We review three recently emerged dermatophytes of public health concern: <i>Trichophyton indotineae</i>, which is causing outbreaks of frequently terbinafine-resistant and difficult-to-treat tinea in South Asia, with cases also reported across six continents; <i>Trichophyton mentagrophytes</i> genotype VII (TMVII), associated with oral and anogenital tinea infections particularly among men who have sex with men in France and the United States; and terbinafine-resistant <i>Trichophyton rubrum</i>, noted as a cause of difficult-to-treat tinea infections, although data are limited. We discuss practical considerations for identifying these pathogens, which relies on DNA sequencing or MALDI-ToF rather than on morphological characteristics. Additionally, we highlight the importance of antifungal susceptibility testing and practical laboratory considerations. Finally, we emphasize the importance of increased adoption of diagnostic testing for suspected dermatophyte infections, as well as the development of rapid, accurate, and affordable dermatophyte testing methods to help improve diagnostic accuracy and judicious antifungal use. Overall, the emergence of severe and antifungal-resistant dermatophyte infections poses a global public health concern. Clinical microbiologists can play a crucial role in addressing this threat by familiarizing themselves with techniques for identifying emerging dermatophyte species and performing antifungal susceptibility testing to guide patient management, monitor trends, and inform future public health interventions.