Terbinafine-Resistant Dermatophytes Isolated in Japan

An epidemiological study of terbinafine (TBF)-resistant dermatophytes was conducted in 2023 as a follow-up to our 2020 and 2022 surveys. Dermatophytes were isolated in 2023 from the same dermatology clinics in Tokyo, Saitama, Shizuoka, and Kumamoto, Japan, as in the previous studies. In total, 311 isolates (122 Trichophyton interdigitale isolates, 1 Trichophyton indotineae isolate, and 188 Trichophyton rubrum isolates) were obtained from 311 human cases of dermatophytosis (195 tinea pedis cases, 54 tinea unguium cases, 28 tinea corporis cases, 27 tinea cruris cases, and 7 tinea manuum cases). Ten strains (1 T. interdigitale strain and 9 T. rubrum strains) were found to be resistant to TBF, and susceptible to efinaconazole, itraconazole, luliconazole, and ravuconazole. The isolation rate of TBF-resistant strains was 2.3% in 2020, 1.4% in 2022, and 3.2% in 2023. We determined the sequences of the squalene epoxidase-encoding gene in 10 TBF-resistant strains, and found that all strains harbored missense and/or deletion mutations. These results indicate that the prevalence of TBF-resistant dermatophytes has increased when compared to the previous studies.