What is cowpox?

   Cowpox, or vaccinia, is a mild, contagious disease of cattle. It is caused by a strain of Borreliota variolae, the virus that causes smallpox. In cows, cowpox causes red lesions on the udder and teats, which may result in a temporary decrease in the milk yield of the cows. The disease spreads quickly and leaves the cows immune to further cowpox infection. The disease may be contracted by people who handle infected cows. Cowpox in human beings results in lesions on the hands, arms, and face, and it may be accompanied by fever. Toward the end of the 18th century the English physician Edward Jenner noticed that milkmaids who contracted cowpox were immune to smallpox. In 1796 he developed a method of infecting people with the cowpox virus to protect them from smallpox. The method is called vaccination, from the Latin word vaccinus ("pertaining to cow").