Key Takeaway:
- Drug-resistant ringworm has spread to 29 countries, with reported cases nearly tripling from 2022 to 2025.
- The fungus can resist terbinafine, making infections harder and longer to treat.
- Limited testing in Africa, India and the Middle East may mean the true global spread is significantly underestimated.
A terbinafine-resistant ringworm fungus has been identified in 29 countries after detections nearly tripled from 2022 through 2025, raising concern about a growing global treatment challenge.
Resistant Fungus Spreads Across Borders
Researchers analysed more than 3,000 laboratory identifications of Trichophyton indotineae, a fungus that often resists terbinafine, a commonly used antifungal drug. The study was published in the CDC’s Emerging Infectious Diseases journal in August.
The researchers found 3,399 T. indotineae identifications from 183 laboratory users in 29 countries during the study period. Annual detections of Drug-Resistant Ringworm rose from 237 in 2022 to 1,692 in 2025.
“Those data revealed a 3-fold increase in T. indotineae identification during 2022–2025,” the researchers wrote, describing the findings as evidence of the fungus’ expanding international spread.
Ringworm is a common fungal infection that can affect the skin, hair, and nails. It typically causes an itchy, scaly rash and can spread through direct contact or contaminated objects, including towels and bedding.
Drug-Resistant Ringworm can cause more extensive infections and may persist when standard treatment fails. The CDC says T. indotineae and other emerging types “may be more severe and difficult to treat than typical ringworm.”
Europe Records Most Cases
Most of the study’s laboratory identifications came from Europe, which accounted for 89.4% of the reported T. indotineae spectra. Researchers cautioned that the concentration does not necessarily mean Europe has the highest underlying infection rate of Drug-Resistant Ringworm.
The study found that 63.8% of participating laboratory users were in Europe, compared with 16.8% in Asia, 15.7% in Latin America, 1.6% in North America, 1.6% in Oceania and 0.5% in Africa. That uneven access to testing affects the picture of where the fungus is spreading.
The researchers said no T. indotineae spectra were identified in Africa and only a few were found in India and the Middle East, despite those regions being known areas where the fungus occurs. They attributed the gaps largely to limited availability and use of mass spectrometry testing.
Limited Testing May Hide Wider Spread
The study said its findings reflect the availability of specialised laboratory equipment and the use of the testing system, meaning the true geographic spread is likely broader than the reported data.
The CDC said the “true number of antimicrobial-resistant ringworm cases is difficult to estimate.” It also noted that identifying T. indotineae generally requires advanced molecular testing that many clinical laboratories cannot perform.
The fungus was first reported in the United States in 2023 after two New York City patients developed severe ringworm that did not improve with oral terbinafine. Laboratory testing later identified T. indotineae.
CDC guidance says health care providers should consider Drug-Resistant Ringworm when infections fail to improve with treatment and may consider specialised testing. Patients should follow antifungal treatment instructions and seek medical advice when treatment is not working.
The researchers called for broader laboratory surveillance, saying improved detection could help health authorities track transmission and guide treatment as the fungus continues to spread internationally.
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