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Published on: December 5, 2020
Emergence of Trichophyton indotineae in Switzerland (2014-2025): Clinical analysis and antifungal susceptibility
Annabel H Lechner1, Dennis D Arnold2, Philipp P Bosshard1
1Department of Dermatology, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
Background And Objectives:
Trichophyton indotineae is an emerging dermatophyte associated with chronic, recalcitrant dermatophytosis and terbinafine resistance due to squalene epoxidase (SQLE) mutations. We analyzed clinical characteristics, antifungal susceptibility profiles, SQLE mutations, and treatment outcomes of cases diagnosed in Switzerland.
Patient And Methods:
Clinical and therapeutic data of patients diagnosed at the University Hospital Zurich (2014-2024) were reviewed. Antifungal susceptibility testing and SQLE gene sequencing were performed for 31 isolates. Additional SQLE data up to December 2025 were analyzed to contextualize temporal trends.
Results:
Thirty-five cases were identified, with a marked increase in recent years. SQLE mutations occurred in 20/31 (65%) study isolates and 55/69 (80%) isolates through 2025, most commonly F397L, L393S, and A448T. Mutated strains exhibited significantly higher terbinafine MICs than wild-type (median 8 vs. 0.008 µg/ml). Patients with SQLE-mutated strains required significantly longer systemic treatment (11.5 vs. 3.5 weeks) and often required itraconazole for eradication, whereas wild-type infections responded to terbinafine. Relapses occurred in one third of patients but generally responded to retreatment.
Conclusions:
Trichophyton indotineae is an emerging cause of dermatophytosis in Switzerland. SQLE genotyping supports individualized therapy; terbinafine remains effective for wild-type strains, itraconazole represents the most reliable option for SQLE-mutated infections.
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