cowpox

Cowpox is a zoonotic viral disease caused by cowpox virus, an Orthopoxvirus related to variola (smallpox) and vaccinia. It primarily affects cattle but can spill over to other mammals, including humans, usually after close contact with infected animals.

Wild rodents are considered the natural reservoir, with domestic cows and cats commonly affected in agricultural settings. Transmission to humans occurs mainly through direct contact with lesions or contaminated materials; occupational groups such as farmers, veterinarians, and milkers are at higher risk. In humans, infection typically results in a localized, crusted lesion at the entry site and is usually mild.

Incubation is typically about 5 to 9 days, and illness rarely includes systemic symptoms. Lesions progress from papules to vesicles to pustules and crusts over several weeks and usually heal without scarring.

Historically, cowpox played a key role in the development of vaccination. In 1796, Edward Jenner observed that milkmaids with cowpox did not contract smallpox and used cowpox material to immunize a boy, establishing the concept of vaccination. Smallpox was later eradicated globally in 1980.

Today, smallpox vaccination campaigns use vaccinia-based vaccines; cowpox virus is not used for routine vaccination and human disease remains rare. The virus is studied in research settings, but human infections are uncommon and generally mild.