Monkeypox is a double-stranded DNA virus and a member of the genus Orthopoxvirus. Human monkeypox was first identified in the Democratic Republic of the Congo (formerly Zaire) in 1970. The first outbreak in the western hemisphere occurred in the spring of 2003. Important epidemiologic and clinical differences exist between human monkeypox in the United States and in Africa, including sex distribution, case fatality, morphology of skin lesions, and associated lymphadenopathy. These divergent clinical presentations could be caused by mode of transmission (skin inoculation vs ingestion), the skin color of affected patients, the training backgrounds of those who saw and documented disease outbreaks, the virulence of monkeypox strains involved, nutritional status, access to advanced medical care, and the prevalence of prior smallpox vaccinations.
