Merck Manual

Please confirm that you are a health care professional

honeypot link

Zoonotic Diseases


James G. H. Dinulos

, MD, Geisel School of Medicine at Dartmouth

Last full review/revision May 2021| Content last modified May 2021
Click here for Patient Education
Topic Resources

Contagious ecthyma and milker's nodules are two viral skin diseases that 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 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

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.

Milker’s nodules

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.

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Also of Interest