A new era of dermatophytes: emerging species, new risk factors, and taxonomic change

SUMMARYThe traditional landscape of dermatophyte infections has changed over the past decade. The emergence and global expansion of Trichophyton indotineae have highlighted the impact of irrational and uncontrolled antifungal and topical corticosteroid use, presented treatment challenges, and highlighted the deficiencies of currently available diagnostic methods. Trichophyton mentagrophytes genotype VII, which has until recently been associated with animal reservoirs, is now associated with human-to-human transmission and is frequently related to sexual transmission. Infections associated with emerging dermatophytes are notable for atypical presentations that may include widespread, inflamed lesions, terbinafine resistance, and frequent relapse. The classic presentation of tinea lesions is frequently obscured by the application of topical corticosteroids, leading to delays in clinical recognition, diagnosis, and appropriate treatment, perpetuating further misuse of topical medications. Deep or invasive dermatophytoses, including Majocchi's granuloma, may occur in immunocompromised patients. The introduction of matrix-assisted laser desorption/ionization-time of flight mass spectrometry and molecular detection of dermatophytes has improved the diagnostic landscape for dermatophytes. However, currently, most assays do not specifically detect T. indotineae or T. mentagrophytes genotype VII, hindering the diagnosis and surveillance. Sequencing of the internal transcribed spacer (ITS) region is required for definitive identification. Terbinafine and azole resistance is common in T. indotineae and increasingly being reported for other species. While nomenclatural changes have been introduced and debated over many decades, the last decade has seen the introduction of new genera, e.g., Nannizzia, Paraphyton, and Lophophyton. An overview of currently recognized dermatophyte species, complexes, and genera is presented here, describing phylogenetic, ecological, and biochemical relatedness. The ethical conundrum of the name Trichophyton indotineae is also discussed.