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What is smallpox?

Smallpox is an infection caused by the virus called variola, a member of the poxvirus family.  It is strictly an infection of human beings.  Animals and insects could neither be infected by smallpox, nor carry the virus in any form.

How is smallpox spread?

Smallpox is acquired from direct contact with individuals sick with the disease, and from contaminated air droplets that expose a susceptible person after having face-to-face contact with the ill person.  Persons with smallpox are most infectious during the first week of illness, 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.  The respiratory tract is the usual entry point for the variola virus into the human being.

What are the symptoms of smallpox?

After the virus enters the body, there is a 12-14 day incubation period during which the virus multiplies, although no symptoms are recognizable.   Initial symptoms include high fever, fatigue, and head and back aches.  A characteristic rash, most prominent on the face, arms, and legs, follow in 2-3 days.  The 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.

What is the treatment for smallpox?

There is no proven treatment for smallpox but research to evaluate new antiviral agents is ongoing.  Patients with smallpox can benefit from supportive therapy (intravenous fluids, medicine to control fever or pain, etc.) and antibiotics for any secondary bacterial infections that occur.

How can smallpox be prevented?

Smallpox infection was eliminated from the world in 1977; routine vaccination ended in 1972.  The level of immunity in vaccinated persons is uncertain; therefore, these persons are assumed susceptible to the infection.  Vaccination against smallpox is not recommended for prevention of the disease in the general public, therefore it is not readily available, but the United States does have an emergency supply of smallpox vaccine.   In people exposed to smallpox, the vaccine can lessen the severity of or even prevent illness if given within 4 days after exposure.  Vaccine against smallpox contains another live virus called vaccinia.  The vaccine does not contain smallpox virus.


See Also...
  CDC's Site:
Overview of smallpox and what CDC is doing to protect you...

Contact Information:

Division of Epidemiology

275 East Main Street
Frankfort, KY 40621

(502) 564-3418 or
(502) 564-3261


Last Updated 2/1/2005