Orf infection

A 45-year-old man presented to the emergency department with an enlarging lesion on the left thumb. The lesion had first manifested as a targetoid papule 2 weeks earlier (Panel A) and had progressively enlarged (Panel B) without associated pain or sensory deficits.

He reported that 3 weeks earlier he had had direct contact with sheep and had been handling meat on a farm. Examination showed an edematous and dusky nodule on the dorsal surface of the left thumb (Panel C). The lesion was unroofed; bacterial, mycobacterial, and fungal cultures of samples from the lesion were negative.

The clinical history of an evolving nodule and direct contact with sheep was consistent with orf. Orf is the cutaneous infection caused by orf virus, a member of the parapoxvirus genus of poxviruses. Orf virus causes oral infections in sheep and goats and can be transmitted to humans through direct contact. The disease typically progresses from a targetoid papule to a boggy nodule, which subsequently dries out and resolves without treatment aside from simple wound care.

In this patient, the unroofed lesion became less edematous (Panel D) and subsequently flattened and dried over the next 3 weeks (Panel E). At follow-up 6 months after onset of the lesion, his thumb had completely healed (Panel F), with only mild residual skin sensitivity.

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