Smallpox is a serious, contagious, and sometimes fatal infectious disease caused by a virus called the variola virus. The disease gets its name from the Latin word for spotted and refers to the small pus-filled blisters that appear on the face and body of an infected person.

Why has smallpox been in the news?

Although smallpox has been eradicated, there is growing concern that terrorists might obtain the smallpox virus and unleash it in a bioterrorist attack.

What are the symptoms of smallpox?

People infected with smallpox develop some symptoms (e.g., fever, headache, backache, and general fatigue) that are typical of many less serious diseases. However, the telltale sign is the development of a unique skin rash. The rash, which has a unique indentation at its center, covers the entire body. The rash progresses to a raised bump, then to a pus-filled blister that crusts and scabs over before finally falling off about 3 weeks later, leaving behind a pitted scar.

How long would it take for symptoms to appear if a person were to come into contact with smallpox?

After exposure, there’s a 7 to 17 day period of time called the incubation period during which time an infected person may not show any symptoms. Then, over the next 2 to 4 days, an infected person may become sick with typical cold and flu-like symptoms (this stage of the disease is called the prodromal stage). The classic smallpox rash begins after these initial cold and flu symptoms disappear. So, the earliest outward symptoms of smallpox would appear would be about 9 days after exposure, when the rash develops.

A person with smallpox is most contagious to others while the rash is present, but is still considered contagious until the last smallpox scab falls off. A person is not contagious during the incubation period and only sometimes contagious during the prodromal stage.

How is smallpox spread?

Smallpox is spread from person to person by several means, including:

  • Direct, face-to-face and fairly prolonged contact with an infected person – the saliva of the infected person can spread the disease
  • Direct contact with the fluid in the blisters in the infected person’s skin or other infected bodily fluids
  • Direct contact with contaminated objects, such as blankets, towels or clothes touched by an infected person

Smallpox is rarely spread through the air in settings such as buses, trains, or office buildings.

Is smallpox fatal?

About 30 percent of people who become infected with smallpox die from their illness.

How is smallpox treated?

There are no drugs to treat smallpox once a person contracts the disease, although drugs can be given to relieve some of the cold and flu symptoms of the disease and other illnesses that might develop in addition to the smallpox. Instead, a vaccine is given to prevent people from contracting the disease in the first place.

Currently, only military personnel who might be exposed to smallpox as a biological weapon of warfare and US healthcare workers ("first responders") are being offered the vaccine. However, enough vaccine has been manufactured to inoculate every man, woman and child in the United States should a bioterrorist attack with smallpox occur. If an outbreak of smallpox were to occur, vaccination within 3 days of exposure will completely prevent or significantly modify the severity of disease in most patients. Vaccination within 4 to 7 days after exposure will likely offer some protection against contracting the disease. The vaccine provides protection from smallpox for 3 to 5 years.

How is the vaccine given?

A two-pronged (bifurcated) needle that has been dipped into the vaccine solution is used to prick the skin of the upper arm several times. The pricking is not deep but will cause a sore spot and one or two droplets of blood to form. If the vaccination is successful, red, itchy bumps develop at the vaccination site followed a few days later by a blister and finally a scab that falls off about 3 weeks later.

Is the smallpox vaccine safe?

The smallpox vaccine offers the best protection against contracting the smallpox virus, which can be fatal. The vaccine itself is not without some risks, however. Based on past history of smallpox vaccination, between 14 and 52 people per 1 million vaccinated will experience a potentially life-threatening reaction, with 1 to 2 of these people dying from these reactions. About 1,000 people per 1 million vaccinated will experience serious but not life-threatening reactions. It is important to note that smallpox cannot be contracted from the vaccine.

In the spring of 2003, several people who receive the vaccine suffered heart attacks and died. The Centers for Disease Control and Prevention (CDC) is conducting an investigation to determine if there is any association between smallpox vaccination and the development of heart problems. Meanwhile, the government agency recommends that anyone with a history of heart disease or suffering from three or more major risk factors for heart disease be excluded from the vaccination program. Risk factors for heart disease include diabetes, high blood pressure, high cholesterol levels, and smoking.

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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 1/18/2010...#10855