A new study from epidemiologists at the Hospices Civils de Lyon (HCL), published in the US journal Emerging Infectious Diseases, suggests that dermatophilosis—a bacterial zoonosis commonly known as “mud fever”—may be transmitted between humans through sexual contact. Until now, this rare infection in humans was primarily observed in farmers or riders who had direct contact with infected horses or cattle.
Between January and June, around forty cases were recorded in France and Spain, with about thirty concentrated in Lyon. The study focused on nine patients who consulted at HCL. Seven of them reported having had sexual intercourse in gay saunas in Lyon—sometimes the same establishments—in the days before lesions appeared.
Although no direct links between members of the cluster were established, the researchers concluded that “genomic similarity and shared sexual exposures strongly suggest human-to-human sexual transmission of this zoonotic bacterium.” All patients were “men who have sex with men in Lyon and Paris.”
Clinical Presentation and Treatment
Symptoms included pustules and crusts on the skin, particularly around the genital area, torso, mouth, and lower limbs. While in animals such superficial lesions can progress to a widespread, potentially fatal form, no patient required hospitalisation. A simple course of antibiotics, “sometimes combined with topical antiseptic care,” led to rapid improvement.
Transmission is believed to occur primarily through skin-to-skin contact, with the humid and warm environment of saunas likely exacerbating the release of zoospores—bacteria capable of moving through water and penetrating the epidermis.
The findings underscore the importance of awareness among healthcare providers and at-risk communities. As Europe continues to grapple with emerging infectious diseases, this study highlights how environmental and behavioural factors can facilitate the spread of pathogens previously confined to occupational exposures.
For context, other recent health-related studies have examined the impact of environmental changes on disease patterns. For instance, human-driven climate change makes rare coastal floods 12 times more likely, which can influence the spread of waterborne pathogens. Meanwhile, research on poverty's impact on children's brain development reminds us that socioeconomic factors also play a critical role in public health outcomes.
The Lyon team plans to continue monitoring for further cases and to investigate potential reservoirs and transmission dynamics. Their work adds a new dimension to understanding how zoonotic diseases can adapt to human-to-human spread in specific social contexts.
