Multicentre survey finds T. mentagrophytes var. indotineae dominated cultured dermatophyte infections in Iran

A multicentre, hospital-based survey of referred dermatophytosis cases in nine Iranian provinces found that Trichophyton mentagrophytes var. indotineae accounted for 1,191 of 1,568 cultured dermatophyte infections, or 76%, during sampling from September 2023 to September 2024. The figure applies to the 1,568 culture-positive cases, not to all 2,211 people investigated for suspected dermatophytosis.

Researchers collected skin, hair and nail specimens from patients attending private mycology clinics and governmental university hospitals in Ardabil, Fars, Golestan, Isfahan, Khuzestan, Mazandaran, Razavi Khorasan, Tehran and West Azerbaijan. Every included patient had fungal elements visible by direct KOH microscopy in at least one sample, and culture recovered dermatophytes from 1,568 of the 2,211 suspected cases, a yield of 70.9%.

The researchers combined a lineage-specific PCR with ITS rDNA sequencing, restriction analysis and haplotype comparisons. The specific PCR identified 1,191 isolates as T. mentagrophytes var. indotineae. Sequencing of 78 randomly selected PCR-positive isolates confirmed their placement within the lineage: 57 represented two sub-genotypes of ITS genotype VIII, while 20 belonged to a previously unrecognised genotype XXIX within the T. mentagrophytes var. indotineae lineage. The study used the variety designation in line with taxonomic databases and recent population-genetic studies.

Clinical forms involving the groin and trunk predominated. Tinea cruris accounted for 656 cultured infections, or 41.8% of the total, followed by tinea corporis with 376 cases, or 23.9%; mixed tinea cruris and tinea corporis accounted for 144 cases, or 9.2%, and generalised infection accounted for 128, or 8.2%. T. mentagrophytes var. indotineae was identified in 544 of 656 tinea cruris cases, 279 of 376 tinea corporis cases, 110 of 144 mixed cruris and corporis cases, and 112 of 128 generalised infections. It was also found in 17 of 29 nail infections and 17 of 45 cases of tinea capitis.

Patients with T. mentagrophytes var. indotineae infection had a mean age of 34.5 ± 13.6 years, a median of 35 and a range of 1–85. The group included 588 males and 603 females, with no statistically significant difference in sex distribution (p = 0.664). Species distribution was associated with age group, province, clinical form and involved body site, with all reported p-values below 0.001. The largest numbers of confirmed infections came from Khuzestan, with 607 cases, followed by Mazandaran with 130 and Ardabil and Fars with 115 each.

Among 73 confirmed cases with reliable patient histories, none had documented travel abroad. This absence of recorded international travel does not establish where infection was acquired, but it means travel alone cannot explain the lineage’s presence in the surveyed population. Retrospective analysis placed several Iranian isolates collected in 2011 and 2015 within genotype VIII, indicating that the lineage was already present before the earliest reports from the Indian subcontinent. The study also identified genotype XXIX, adding to previously reported local genetic diversity. Related lineages have been recovered from sheep in rural Iran, but a local animal reservoir remains an unconfirmed hypothesis, and the data do not resolve the lineage’s geographic origin or centre of diversity.

Partial sequencing of the squalene epoxidase gene, SQLE, in 410 T. mentagrophytes var. indotineae isolates detected mutations in 184 isolates, or 44.8%. The mutations comprised the F397L amino-acid substitution in 132 mutant isolates, representing 71.7%, and L393S in 52, representing 28.3%. Mutation proportions were highest in Khuzestan at 52.4% and Fars at 46%, and lowest in Golestan at 8.5%. Both substitutions have previously been associated with terbinafine resistance in isolates from Asia and Europe. The reported 44.8% frequency was higher than mutation rates of 17.8% in an Iranian survey from 2020 and 14.35% in one from 2024, although the present study sequenced only part of the SQLE gene and targeted mutations at positions 393 and 397, so other mutations may not have been detected.

No antifungal susceptibility testing was performed, and the study did not collect clinical outcome data demonstrating treatment failure. The findings therefore identify a substantial proportion of isolates carrying mutations associated with likely terbinafine resistance, but they do not directly establish phenotypic resistance or explain individual treatment outcomes. The hospital-based design and reliance on patients referred to specialised clinics also limit how directly the observed proportions can be applied to Iran’s general population.

Overall, the survey documents a major shift in the epidemiology of referred dermatophytosis in Iran: T. mentagrophytes var. indotineae was the leading identified cause across the sampled settings and was detected in skin, scalp and nail infections. The authors said the findings highlight the need for routine molecular identification, SQLE genotyping and stronger national surveillance, while broader genomic studies and integration of clinical outcome data are needed to clarify transmission, origin and therapeutic implications.

Subject of Research: Epidemiology and terbinafine-resistance-associated SQLE mutations in Iranian dermatophyte isolates

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

Article References: Takesh, A., Wennrich, A., Kolařík, M., Zarei-Mahmoudabadi, A., Kiasat, N., Pazyar, N., Rafiei, A., Abastabar, M., Haghani, I., Kharazi, M., Basiri, S., Jahanshiri, Z., Khodadadi, H., Mohammadi, R., Zarrinfar, H., Seifi, Z., Diba, K., Kamali Sarvestani, H., & Rezaei-Matehkolaei, A. (2026). Dermatophytosis in Iran: a sharp increase in cases caused by Trichophyton mentagrophytes var. indotineae. IMA Fungus, 17, Article e180817. https://doi.org/10.3897/imafungus.17.180817

Image Credits: AI Generated

DOI: 10.3897/imafungus.17.180817

Keywords: dermatophytosis, Trichophyton mentagrophytes, T. mentagrophytes var. indotineae, Iran, terbinafine resistance, SQLE mutations, tinea cruris, tinea corporis, molecular surveillance, fungal infection, sharp, increase