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Two viral skin diseases are rarely transmitted from animals to humans.
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
Patients can develop regional adenopathy, lymphangitis, and fever.
Diagnosis 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 is by history of contact and cutaneous findings. Differential diagnosis varies depending on morphology but can include primary inoculation TB (a chancre that can develop at the site of TB inoculation), sporotrichosis, anthrax, and tularemia. Lesions heal spontaneously; no treatment is necessary.
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