Experts warn doctors and the public about the emergence of difficult-to-treat fungal skin infections in the USA

Health care providers should be wary of new and highly contagious forms of ringworm, or tinea cruris, that are evolving into a potential public health threat, according to two reports.

In the first of these studies, experts at NYU Langone Health who focus on the spread of contagious skin rashes document the first reported case in the United States of a sexually transmitted fungal infection that can take months to clear up, even with treatment.

In the second report, doctors at NYU Langone teamed up with officials from the New York City Department of Health to describe the nation’s largest group of patients suffering from a similar strain of fungus that is resistant to standard therapies.

Both types of fungus belong to a group that causes rashes, or tinea, that spread easily to the face and limbs (ringworm), groin (jock itch) and feet (athlete’s foot). However, the tinea examined in the new reports can look quite different from the neat, regular circles seen in most forms of ringworm. They can instead be mistaken for lesions caused by eczema, and so can go for months without proper treatment.

The first report, which appeared online in the magazine on June 5 JAMA Dermatologydescribes a man in his thirties who developed ringworm on his penis, buttocks, and limbs after returning to New York City from a trip through England, Greece, and California.

Genetic testing of fungal samples taken from the patient’s rashes showed that the infection was caused by the species Trichophyton mentagrophytes type VII (TMVII). This sexually transmitted form of ringworm is increasingly diagnosed across Europe. In 2023, 13 cases were reported in France, mostly in men who have sex with men. Notably, the man in the current study reported having had sex with several male partners during his travels, none of whom reported similar skin problems.

“Healthcare providers should be aware that Trichophyton mentagrophytes type VII is the latest in a group of serious skin infections that has now reached the United States,” said lead study author and dermatologist Avrom Caplan, MD. Caplan is an assistant professor in the Ronald O. Perelman Division of Dermatology at NYU Grossman School of Medicine.

“Because patients are often hesitant to discuss genital problems, physicians need to ask directly about rashes in the groin and buttocks, especially in sexually active patients who have recently traveled abroad and report itchy spots elsewhere on the body,” added lead study author Dr. John Zampella.

Zampella, an associate professor in the Ronald O. Perelman Department of Dermatology at NYU Grossman, says that while infections caused by TMVII are difficult to treat and can take months to clear, so far they seem to respond to standard therapies with antifungals such as terbinafine.

Meanwhile, Caplan says the new skin condition examined in his other new report poses a greater challenge for dermatologists. The study results, published online in May, JAMA DermatologyFocus on Trichophyton indotineae (T. indotineae), which is widespread in India and now reported worldwide. The infection, first confirmed in the United States last year, causes similar itchy and contagious rashes as TMVII, but often does not respond to treatment with terbinafine.

To better understand how T. indotineae can evade antifungals, researchers collected clinical and laboratory data from 11 men and women treated for ringworm in New York City hospitals between May 2022 and May 2023. Their tinea was confirmed to be caused by T. indotineae. Seven of the patients had received standard doses of terbinafine for periods ranging from 14 days (the usual duration for most forms of ringworm) to 42 days, but their rashes did not improve.

When analyzing the DNA of the fungal samples, the team discovered several variations in the genetic code (mutations) that prevent terbinafine from docking onto fungal cells and drilling holes in their protective membranes. According to the study authors, these mutations could help explain why the therapy failed to fight the infections in some cases.

The results also showed that three patients made a full recovery and two patients improved when treated with another antifungal drug called itraconazole. The problem with this therapy, however, according to Caplan, is that while the drug is effective, it can interact with many other medications and cause nausea, diarrhea and other side effects that make long-term use difficult.

“These findings provide new insight into how some of the fungal skin infections originating in South Asia can evade our standard therapies,” Caplan said. “Physicians must not only learn to recognize their misleading signs, but also ensure that their treatment meets the quality of life needs of each patient.”

Caplan adds that over the next few months he plans to work with leading fungal experts in the U.S. and internationally to expand research efforts and track emerging cases.

The researchers point out that while dermatologists should monitor their patients for signs of TMVII and T. indotineae, rates in the United States remain low.