This disease presents as exudative dermatitis characterized by the formation of crusty scabs, pustules, and scaling lesions. Infections often appear as pitted keratolysis, folliculitis, or lesions resembling ringworm (erythematous, scaly, oval patches). Ringworm is caused by a fungus whereas rain rot is bacterial.

Dermatophilosis, also known as rain rot or lumpy wool disease, is a contagious bacterial skin infection caused by the Gram-positive actinomycete Dermatophilus congolensis. It primarily affects domestic livestock such as cattle, sheep, goats, and horses, as well as wild cervids and occasionally humans.

The disease is characterized by exudative dermatitis that results in raised, matted hair tufts resembling paintbrushes, thick crusts, and alopecia (hair loss). Key clinical features include:

Lesion Location: Typically appears on the back, neck, face, and legs, areas prone to moisture and abrasion.

Diagnosis: Confirmed via microscopic demonstration of a "railroad track" appearance of bacterial septate forms in Giemsa-stained smears.

Transmission: Spread through direct contact with infected animals, contaminated fomites, or arthropod vectors like flies and ticks.

Predisposing factors include prolonged wet weather, high humidity, skin trauma, and compromised immune systems. While often self-limiting in healthy animals, it causes significant economic losses through reduced productivity and hide damage. Treatment involves systemic antibiotics (e.g., penicillin, oxytetracycline) combined with topical antiseptics (e.g., copper sulfate, iodine) and environmental management to keep animals dry. Recent medical literature (2025–2026) also indicates rare instances of human-to-human sexual transmission among specific populations, expanding the understanding of its zoonotic potential.

Suspected Sexual Transmission of Dermatophilosis among Men Who Have Sex with Men, Barcelona, Spain, 2025–2026