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Smallpox
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Smallpox is a viral infection that was eliminated from the world in 1978. It is caused by the variola virus. The incubation period is about 12-14 days (range: 7 to 17 days) following exposure. Initial symptoms include high fever, fatigue, head and back aches, and sometimes vomiting. Two to three days later, a rash appears that starts as red spots on the tongue and mouth before progressing within 24 hours to the characteristic body rash, most prominent on the face and arms. The body rash starts with flat red lesions that evolve at the same rate. Lesions become pus-filled and begin to crust early in the second week. Scabs develop and then separate and fall off after about 3-4 weeks. The majority of patients with smallpox recover, but death occurs in up to 30% of cases.
Smallpox is usually spread from one person to another by infected saliva droplets that expose a susceptible person having face-to-face contact with the ill person. Persons with smallpox are most infectious during the first week of the rash, because that is when the largest amount of virus is present in saliva. However, some risk of transmission lasts until all scabs have fallen off. Rarely, smallpox virus has been spread from one person to another through airborne or fomite transmission.
Routine vaccination of the American public against smallpox ended in 1972. The level of immunity, if any, among persons who were vaccinated before 1972 is uncertain; therefore, these persons are assumed to be susceptible.
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Variola Virion
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To learn more about smallpox, visit the CDC Emergency Preparedness & Response Smallpox Information web site.
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