Dermatophilus congolensis

Dermatophilosis is a bacterial skin disease in animals caused by Dermatophilus congolensis. It occurs worldwide, but is most common in tropical and subtropical regions. Domestic animals commonly affected include cattle, sheep, goats, and horses. Wild animals affected include deer, rabbits, rodents, woodchucks, striped skunks, raccoons, foxes and a captive polar bear. Dermatophilus congolensis thrives in wet, humid conditions and is referred to as rain rot, rain scald, or strawberry foot rot.

The bacterium can be transmitted to animals by direct contact and by arthropods, such as ticks and biting flies. The most likely sites of infection include wet skin, cuts, and abrasions. As the bacteria invade the skin, it becomes inflamed and epithelial cells proliferate. Crusts of exudate and shed skin cells accumulate trapping hair. When crusts drop off, the underlying skin is red, inflamed, and often bleeding.

Clinical signs include raised, matted tufts of hair, crusts, and hair loss. Lesions typically occur on parts of the body that are chronically wet or subject to cuts and abrasions, such as the back, face, ears, and legs.

Dermatophilosis can be transmitted to people through direct contact with an infected animal. But in France and Spain, researchers have diagnosed the condition in a number of men who have sex with other men and had no known exposure to affected animals. Across Europe, more than 25 cases have been confirmed. These cases suggest that Dermatophilus congolensis can be transmitted from human-to-human by sexual contact.

Diagnosis of Dermatophilosis can made by microscopic examination of stained skin crusts and identification of the classic morphology of rows of Gram-positive bacteria in hypha-like arrangements. Definitive diagnosis can be made by culturing the bacteria from skin lesions on Columbia 5% sheep blood agar. Dermatophilus congolensis produces small yellowish-beta-hemolytic colonies. Gram stain reveals gram-positive coccoid forms occasionally arranged in irregular filaments with transverse septa. Definitive diagnosis can ben made using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

References

Habte D, Addis H, Wondimagegnehu K. Clinical and Laboratory Diagnosis of Dermatophilosis (Cutaneous Streptothricosis) in Cattle in Ethiopia: Case Report. Vet Med Sci. 2025 Mar;11(2):e70245. doi: 10.1002/vms3.70245.

Descalzo V, et al. Suspected Sexual Transmission of Dermatophilosis among Men Who Have Sex with Men, Barcelona, Spain, 2025–2026, Emerg Infect Dis. 2026 Jun. https://doi.org/10.3201/eid3206.260476