Hantavirus, mpox, and now dermatophytosis. Once again, alarm bells are ringing due to the emergence of human-to-human transmission cases of a primarily zoonotic disease. Fortunately, however, there is no cause for alarm in this case: the cases of this skin infection recently detected in Barcelona present mild symptoms and respond well to antibiotic treatment. Nevertheless, they do prompt reflection on why we are increasingly encountering cases of zoonotic diseases that are also capable of human-to-human transmission.

The History of Dermatophytosis in Humans

Dermatophilosis is an uncommon skin infection in humans caused by bacteria of the genus Dermatophilus. To date, cases reported in the scientific literature have been linked mainly to people in contact with animals, particularly in elephant sanctuaries in Thailand and in aquatic environments, where the bacteria can spread more easily because they release zoospores — microscopic, motile forms that move through humid conditions — Vicente Descalzo-Jorro told Univadis Spain, part of Medscape’s Professional network.

Descalzo-Jorro is an internal medicine specialist working in the sexually transmitted infection (STI)/HIV unit at Drassanes-Hospital Vall d’Hebron in Barcelona, Spain. His primary research interest is in emerging sexually transmissible infections.

Cases in Barcelona

To date, “10 cases have been confirmed in Barcelona between December 2025 and April 2026, and there are two highly probable cases pending confirmation from late May,” Descalzo-Jorro noted.

The patients were men who have sex with men and presented with mild skin lesions, including rashes, papules, or nodules, most commonly affecting the genital area, groin, thighs, or beard region — all sites potentially exposed to skin-to-skin contact during sexual activity. All patients responded well to antibiotic treatment and recovered without complications.

Clinical, epidemiologic, and genomic findings from the nine cases diagnosed between December 2025 and March 2026, published in Emerging Infectious Diseases, point to possible person-to-person transmission in the setting of intimate or sexual contact.

It is also highly likely that the number of cases will continue to rise. Since news of the dermatophytosis cases in Barcelona became public, many people with lesions consistent with the infection have sought medical consultation — a sign of how important it is for the public to be well informed about health issues.

Saunas and Geographic Mobility: Key Factors in Transmission

The emergence of cases took the Drassanes-Vall d’Hebron STI unit by surprise. “At first, the detection in December of the first case following a microbiological culture from a person with skin lesions seemed somewhat anecdotal to us, and we had to begin researching because none of us were familiar with dermatophytosis. However, within a week we detected two more cases, and Vall d’Hebron Hospital reported two additional cases, which put us on high alert. All these cases involved men who had recently visited saunas to have sex with other men, who had not traveled or been in contact with animals, which is why the hypothesis of human-to-human transmission gained significant traction,” explained Descalzo -Jorro.

The fact that they had visited saunas to engage in sexual contact is a key factor in explaining these infections as saunas are humid environments that facilitate the transmission of zoospores.

Descalzo-Jorro explained, the hypothesis, therefore, is that an unidentified man traveled to Southeast Asia, came into contact with infected elephants in humid environments, and then, after returning to Europe — where cases have also been detected in Lyon and Paris — went to a sauna to have sexual contact with other men, thereby initiating the chain of transmission.

This hypothesis of a recent common origin is reinforced by the fact that microbiological and genomic analysis of the samples indicated that the identified microorganisms were very similar to one another and, in turn, very different from the strains identified to date, “so it is likely that we are dealing with a new species of Dermatophilus,” said Descalzo -Jorro.

Measures to Be Taken

As has been seen with other recent emerging diseases such as hantavirus, mpox, and COVID, globalization facilitates their emergence and spread. “However, there is nothing we can do about this: society is becoming increasingly globalized, so we must focus on prevention and detecting cases as early as possible,” Descalzo-Jorro explained.

In this context, the Study Group on STIs of the Spanish Society of Infectious Diseases and Clinical Microbiology has distributed an informational document to its members detailing these cases of dermatophytosis and another similar cluster detected simultaneously in Lyon and Paris. The document notes that the disease may be emerging as a transmissible bacterial dermatosis within sexual networks with high exposure. Following this report, researchers have become aware of new compatible cases in other cities across Spain, including Madrid and Guipúzcoa as well as elsewhere in Europe, suggesting that this is not strictly a local phenomenon and that we may be facing an emerging skin infection that is likely underdiagnosed.

Therefore, “although further studies are still needed to precisely determine the scope and transmission mechanisms involved, it is important to increase clinical suspicion of compatible skin lesions, promote the collection of microbiological samples, and foster coordinated surveillance among STI, microbiology, and public health units,” concluded Descalzo-Jorro.

Descalzo-Jorro and the other authors of the study declared having no conflicts of interest.

This story was translated from Univadis Spain, part of the Medscape Professional Network.