Add to ORKGMonkeypox is a rare disease caused by the monkeypox virus, a member of the same group of viruses as smallpox virus. The monkeypox virus can spread from animals to humans and sometimes from one person to another. In humans, monkeypox causes fever, headache, backache, and swollen lymph nodes, followed by a blister-like rash. In some cases, monkeypox can cause death.In early June 2003, monkeypox was reported among several people in the United States who got sick after having contact with sick pet prairie dogs. This is the first outbreak of human monkeypox in the United States.Because the monkeypox virus is related to the virus that causes smallpox, the smallpox vaccine can protect people from getting monkeypox as well as smallpox