A fungus that causes a severe, hard-to-treat form of ringworm has now turned up in 29 countries, according to a new analysis of years of diagnostic lab data. The organism resists the antifungal pill doctors reach for first, which means infections that would normally clear in weeks can instead drag on for months while patients cycle through treatments that do not work.
Identifications rose from 237 to 1,692 in three years
Researchers tracked a sharp rise in confirmed cases of Trichophyton indotineae between 2022 and 2025, with annual identifications climbing from 237 to 1,692 over that span, roughly a sevenfold increase. The findings come from an analysis of submissions made by more than 500 diagnostic laboratory users across 54 countries during that period, with the fungus itself confirmed present in 29 of them.
That rate of increase is what has drawn attention from infectious disease researchers, since it suggests the fungus is not simply being detected more often because labs are looking harder, but is genuinely spreading into new regions and infecting more people year over year, according to reporting on the study by NewsNation.
Resistant to the standard first-line pill
Trichophyton indotineae is resistant to terbinafine, the oral antifungal medication most commonly prescribed as a first-line treatment for ringworm and related skin infections. When the standard pill fails to clear an infection, patients are often left cycling through longer courses of the same ineffective drug, or moving on to alternative antifungals that may carry more side effects, cost more, or simply work less reliably against this particular strain.
The practical result for patients is an infection that persists for months rather than clearing in the two to four weeks typical of standard ringworm cases treated successfully with terbinafine. Because the visible rash can improve temporarily even when the underlying infection has not been eliminated, some patients and even some clinicians may not immediately recognize that a case has become drug-resistant rather than simply slow to heal, a pattern Gizmodo reported has contributed to infections lingering for months at a time.
A related genomic study spans 14 countries
A separate genomic investigation, published independently of the MSI surveillance analysis, examined Trichophyton indotineae samples collected across 14 countries to trace how the resistant strain has moved and mutated as it spread. That kind of genomic work complements the broader case-count surveillance by showing whether resistant fungus turning up in different regions traces back to a single point of origin or has emerged through separate, unrelated mutations, information that matters for predicting how quickly resistance might continue to spread and whether new resistant lineages could still be emerging independently.
Findings from that genomic work have generally reinforced the surveillance data: the resistant strain is not confined to the region where it was first characterized but has established itself across multiple continents, with genetic markers suggesting both long-distance spread of existing resistant lineages and, in some cases, resistance developing locally under similar treatment pressures.
Where the tracking data comes from
The findings draw on the MSI project, a surveillance database hosted by the Parasitology-Mycology Laboratory at Pitie-Salpetriere University Hospital in France. The project allows diagnostic labs around the world to submit samples from patients with suspected fungal infections into a single shared system, which includes a reference library covering roughly 1,700 different fungal species that helps individual labs identify rare or unfamiliar organisms they might not otherwise be equipped to distinguish.
Centralized surveillance systems like MSI matter for a pathogen such as this one precisely because no single country’s public health agency is likely to spot a slow-building global trend from its own case data alone; a few dozen cases in any one nation might look like a local anomaly, while the same cases pooled across 54 countries reveal a clear upward pattern.
A skin infection with a wider public health signature
Trichophyton indotineae causes dermatophytosis, the general term for fungal infections of the skin, and produces symptoms similar to common ringworm: red, itchy, often ring-shaped rashes that can appear on the body, groin, feet, or scalp. What sets this species apart is not the appearance of the rash but its resistance profile, which the study’s authors describe in the CDC journal Emerging Infectious Diseases as revealing a marked global increase in identification of the organism.
Researchers have linked the fungus’s spread partly to global travel and partly to inconsistent or incomplete antifungal treatment in regions where it first became established, conditions that can allow a resistant strain to persist and move between populations rather than dying out. Because ringworm is common, mild in most cases, and often self-diagnosed or treated with over-the-counter creams before a doctor ever sees it, health officials say wider awareness of a resistant strain is part of what is needed to keep prolonged, treatment-resistant cases from continuing to climb.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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