Tinea — commonly called ringworm — is a common, highly contagious infection of the skin, hair or nails caused by dermatophyte molds, most often of the genus Trichophyton. It spreads by skin-to-skin contact with infected people or animals, from one part of the body to another, and through contaminated objects. Most cases stay local and clear with an antifungal cream; pills are usually kept for extensive infections, infected hair follicles, or cases that creams don't clear.
Over the past decade, a much worse form has spread across South Asia.
A new species, and a resistant one
The cause is Trichophyton indotineae, first identified as T. mentagrophytes ITS genotype VIII until genomic studies showed it was different enough to be a species of its own.
| What it looks like | widespread, inflamed, itchy plaques on the body (tinea corporis), the groin, pubic area and inner thigh (tinea cruris), or the face (tinea faciei) |
| How it behaves | highly transmissible, and often resistant to terbinafine, a mainstay of treatment |
| What likely drove it | misuse and overuse of topical antifungals and corticosteroids — especially widely sold combination creams mixing antifungals, antibiotics and high-potency steroids |
| Where it had been reported | throughout Asia, in Europe and in Canada — but never before in the United States |
Two patients in New York City
On February 28, 2023, a New York City dermatologist told public health officials about two unrelated patients whose severe tinea had not improved on oral terbinafine. A clinical lab had identified both fungi as T. mentagrophytes. The New York State Department of Health's Wadsworth Center sequenced them in March 2023 and found both were T. indotineae.
| Patient A | Patient B | |
|---|---|---|
| Who | a woman aged 28, no other medical conditions | a woman aged 47, no major medical conditions |
| Rash began | summer 2021 | summer 2022, while in Bangladesh |
| Travel or contacts | no recent international travel, no known contact with anyone with a similar rash | several relatives in Bangladesh had similar rashes; her husband and son at home reported them too and were being evaluated |
| Where on the body | large, ring-shaped, scaly, itchy plaques on the neck, abdomen, pubic area and buttocks | widespread, separate, scaly, ring-shaped itchy plaques on the thighs and buttocks |
| Treatment | first seen in December 2021, in the third trimester of pregnancy; oral terbinafine from January 2022, after the birth — no better after 2 weeks; switched to itraconazole, and the rash cleared after a 4-week course | antifungal-steroid creams in Bangladesh; three emergency visits in autumn 2022 (hydrocortisone ointment and diphenhydramine; clotrimazole cream; terbinafine cream) — no improvement; 4 weeks of oral terbinafine — no improvement; 4 weeks of griseofulvin — about 80% better |
| Status at the report | being watched for a return | itraconazole under consideration |
What it means
- Local spread is possible. Patient A hadn't travelled abroad, which suggests T. indotineae may be passing between people in the United States.
- Suspect it in widespread tinea, especially when it doesn't respond to first-line antifungal creams or to oral terbinafine.
- Standard lab methods get it wrong. Culture-based identification, used by most clinical labs, usually misidentifies it as T. mentagrophytes or T. interdigitale; correct identification needs genomic sequencing. Clinicians who suspect it should contact their state or local health department, which can help arrange testing at certain public health labs and specialized academic and commercial labs.
- Itraconazole can work, with caveats: its absorption varies, which makes blood levels uneven; it interacts with other drugs; treatment can take up to 12 weeks; and resistance to triazoles like it has already been documented.
- Stewardship matters: cutting misuse and overuse of prescription and over-the-counter antifungals and steroids.
- Clinicians can teach patients how to avoid spreading ringworm (CDC advice), and more surveillance and testing could track the fungus's spread.
Sources
Based on Caplan AS, Chaturvedi S, Zhu Y, et al., "Notes from the Field: First Reported U.S. Cases of Tinea Caused by Trichophyton indotineae — New York City, December 2021–March 2023," MMWR volume 72, number 19, Centers for Disease Control and Prevention, with authors from CDC, NYU Grossman School of Medicine, the New York State Department of Health and the New York City Department of Health and Mental Hygiene; a work of the United States government in the public domain. Clinical photographs of the patients' skin, taken by outside physicians and used with the patients' permission, are left out.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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