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Two viral skin diseases are rarely transmitted from animals to humans.

Contagious ecthyma: Contagious ecthyma (contagious pustular dermatitis) is caused by orf virus, a poxvirus that infects ruminants (most often sheep and goats). Farmers, veterinarians, zoo caretakers, and others with direct animal contact are at risk. The cutaneous findings pass through 6 stages that together last about 1 wk:

• Stage 1 (papular): A single red edematous papule on a finger (most commonly right index finder)
• Stage 2 (target): A larger nodule with a red center surrounded by a white ring with a red periphery
• Stage 3 (acute): A rapidly growing infected-looking tumor
• Stage 4 (regenerative): A nodule with black dots covered with a thin transparent crust
• Stage 5 (papillomatous): A nodule with a surface studded with small projections
• Stage 6 (regressive): A flattened nodule with a thick crust

Ecthyma (Contagious)

Patients can develop regional adenopathy, lymphangitis, and fever.

Diagnosis is by history of contact; differential diagnosis is extensive depending upon the stage of the lesion. Acute lesions must be differentiated from milker's nodules, Mycobacterium marinum infection, and other bacterial infections; regressed lesions must be differentiated from cutaneous tumors, such as Bowen's disease or squamous cell carcinoma. Lesions spontaneously heal; no treatment is necessary.

Milker's nodules: These are caused by paravaccinia virus, a parapoxvirus that causes udder lesions in cows. Infection requires direct contact and produces macules that progress to papules, vesicles, and nodules. This infection has 6 stages, which are similar to those of contagious ecthyma. Fever and lymphadenopathy are uncommon. Diagnosis is by history of contact and cutaneous findings. Differential diagnosis varies depending upon morphology but includes primary inoculation TB, sporotrichosis, anthrax, and tularemia. Lesions heal spontaneously; no treatment is necessary.

Milker's Nodule

Last full review/revision October 2008 by James G.H. Dinulos, MD

Content last modified October 2008