Last Reviewed: October 2011

What is smallpox?

Smallpox is an acute, contagious and sometimes fatal disease caused by the variola virus and marked by fever and a distinctive progressive skin rash.

Who gets smallpox?

The last naturally occurring case of smallpox occurred in Somalia in 1977 and the World Health Organization has considered the disease eradicated since 1979. The last occurrence of the disease in the United States was in 1949. However, given the threat of bioterrorism since September 11, 2001, it is considered a disease that could be intentionally released during a bioterrorist attack.

How is smallpox spread?

Smallpox spreads from contact with infected persons. Generally, direct and fairly prolonged face-to-face contact is required to spread smallpox from one person to another. Smallpox also can be spread through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing.

What are the symptoms of smallpox?

The symptoms of smallpox begin with high fever, head and body aches and sometimes vomiting. A rash follows that spreads and progresses to raised bumps and pus-filled blisters that crust, scab and fall off after about three weeks, leaving a pitted scar.

How soon after infection do symptoms appear?

After exposure, it takes between 7 and 17 days for symptoms of smallpox to appear (average incubation time is 12 to 14 days). During this time, the infected person feels fine and is not contagious.

How is smallpox diagnosed?

Smallpox can be diagnosed based on the patient's clinical signs and symptoms. The disease can be definitively diagnosed by isolation of the virus from the blood or lesions, or by identification of antibodies in the blood made in response to the virus. The diagnosis of smallpox is made in specialized laboratories with appropriate testing techniques and measures to protect the laboratory workers.

What is the treatment for smallpox?

Vaccine administered up to four days after exposure to the virus, and before the rash appears, provides protective immunity and can prevent infection or lessen the severity of the disease. No effective treatment, other than the management of symptoms, is currently available. A number of compounds are under investigation as chemotherapeutic agents.

What can be done to prevent the spread of smallpox?

If the virus were to present itself again it could be prevented by vaccination of close contacts of those who have been infected.