Zoonotic Skin Diseases

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 week:

• 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)

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Contagious ecthyma is a focal skin lesion caused by orf virus infection, usually occurring on a finger and transmitted to animal workers from sheep or goats. The lesion passes through 6 stages; this image shows the 2nd stage (target), characterized by a large nodule with a red center surrounded by a white ring and a red periphery.

Image courtesy of the National Institute for Occupational Safety and Health.

Patients can develop regional adenopathy, lymphangitis, and fever.

Diagnosis of contagious ecthyma is by history of contact; differential diagnosis is extensive depending on the stage of the lesion. Acute lesions must be differentiated from milker’s nodules, Mycobacterium marinum infection (see Cutaneous disease), and other bacterial infections; regressed lesions must be differentiated from cutaneous tumors, such as Bowen disease or squamous cell carcinoma.

Lesions spontaneously heal; no treatment is necessary.

These nodules are caused by paravaccinia virus, a parapoxvirus that causes udder lesions in cows. Infection requires direct contact and causes 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 of milker's nodules is by history of contact and cutaneous findings. Differential diagnosis varies depending on morphology but can include primary inoculation tuberculosis (a chancre that can develop at the site of tuberculosis inoculation), sporotrichosis, anthrax, and tularemia.

Lesions heal spontaneously; no treatment is necessary.

Milker's Nodule

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Milker’s nodule is a focal skin lesion caused by paravaccinia virus, a parapoxvirus that causes udder lesions in cows. The lesion passes through 6 stages; this image shows the stage in which a single red edematous papule develops from an initial macule.

Image courtesy of the National Institute for Occupational Safety and Health.