The incubation period in humans ranges from 5-28 days, followed by the appearance of violaceous nodules that may be smooth, verrucous, or, less commonly, pustular or bullous. Lesions may be surmounted by a superficial grayish crust. Classically, 1-5 lesions are present on an affected individual, each roughly 0.6-2 cm. Mild constitutional symptoms such as low-grade fever, regional lymphadenitis, and moderate leukocytosis and eosinophilia may be present. The lesions of milker's nodules may be painful on direct pressure. Although rare, milker's nodules may be spread from person to person via direct contact. The condition usually resolves in about 6 weeks.
A detailed patient history will typically elicit exposure to a cow, usually through milking. The cow may actually have papular, pustular, vesicular, or crusted lesions upon the teats and possibly other areas. Lesions in cattle are often accompanied by alopecia. Epidemics affecting many animals within a herd are common. Infections in cows are thought to be spread by contact, either through milking machines or the farmers.
B08.03 – Pseudocowpox [milker's node]
27240009 – Milker's nodule
Differential Diagnosis & Pitfalls
- Ecthyma – A simple bacterial infection caused by Staphylococcus aureus.
- Halogenoderma (bromide and iodide eruptions) – Differentiated by a specific exposure to ingestants containing these halides.
- Tuberculosis verrucosa cutis – Red papular nodules in the skin that may appear 2-4 weeks after inoculation by Mycobacterium tuberculosis in a previously infected and immunocompetent individual.
- Primary or secondary syphilis – Distinguished by a history of sexually transmitted disease and performance of a rapid plasma reagin (RPR) or Venereal Disease Research Laboratory (VDRL) test.
- Cowpox – This is a rare condition more often associated with cats and rodents rather than cattle.
- Ecthyma contagiosum (orf) – A similar condition caused by a similar parapox virus that typically affects sheep rather than cows.