The last naturally acquired case of smallpox in the world occurred in October 1977 in Somalia. The World Health Organization officially certified the world as smallpox-free in 1979. Two secure laboratories, the Centers for Disease Control and Prevention (CDC) in the United States and one in Russia, are the only known holders of the virus.
Smallpox is spread by droplet and aerosol; it may also be spread by direct inoculation from a lesion to an open wound or cut in the skin. Weaponized smallpox has been postulated to be spread by aerosol. Transmission is usually limited to close contacts such as household members. The incubation period is from 7 to 17 days; patients are infectious once the rash and/or oral lesion has appeared.
Smallpox disease is distinct from other general body rashes.
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