December 2010

What Is Smallpox?

Smallpox is a disease caused by Variola virus. Smallpox was once a very common and deadly disease. After the World Health Organization (WHO) led a global effort to eradicate smallpox through vaccinations, the last natural case of smallpox was reported in 1977. In 1978 there was a case of laboratory-acquired smallpox. In 1980 the WHO declared the disease eradicated and there have been no cases in the world since that time.

The only known quantities of the smallpox virus are housed in government-controlled laboratories in the U.S.A. and Russia. There are concerns that there may be unknown sources that may be used for bioterrorist activities.

There are two forms of smallpox:

  • Variola major is the more common form of smallpox, with approximately 30% mortality rate.
  • Variola minor is the less common form of smallpox, with less than one percent mortality rate.

How Can I Get Smallpox?

Smallpox occurs only among humans and is passed from person to person. In most cases, smallpox is spread by an ill person to others through infectious droplets from coughing or sneezing. Contaminated clothing or bed linen could also spread the virus.

What Are the Signs and Symptoms of Smallpox?

It may take 12 – 17 days from the time of contamination for a person to develop symptoms of smallpox. Initial symptoms include fever, malaise, aching pain, backache and headache. A characteristic rash then appears two to three days later, mainly inside the mouth and on the face and forearms, spreading to the trunk and legs. A person is most contagious during the first week of illness.

The rash may appear on all parts of the body, including the palms and soles, and the eruptions all progress at a similar pace. The rash eventually evolves into scabs. In contrast, chickenpox does not affect the palms and soles, tends to be concentrated on the abdomen, and may have eruptions that develop at a different rate.

What Is the Treatment?

Currently, there is no treatment for smallpox, although people ill with smallpox can benefit from supportive therapy (intravenous fluids, medicine to control fever, etc.) and antibiotics for any secondary bacterial infection that can occur. In addition, research to see if newer anti-viral medications will help against smallpox is ongoing.

Is There a Vaccine for Smallpox?

The vaccine that was given to people prior to eradication is no longer produced. The vaccine was quite effective; however, there were many incidences of severe adverse reactions especially in people with certain health conditions such as eczema, or poor immune systems. Routine mass vaccinations are not currently recommended unless a case is reported.

The Canadian government has about 300,000 doses of stored vaccine and the U.S. has approximately 6-7 million doses. Currently, vaccinations are reserved for laboratory workers who work directly with the virus. There is no vaccine available for the general public. It is suspected that individuals who received childhood immunizations prior to 1977 have partial immunity at best. Research into a more effective and safer vaccine is ongoing.

Can I Get Treatment If I Have Been Exposed but Do Not Have Symptoms?

Yes, if the vaccine is given within four days of exposure to smallpox, it can lessen the severity of the disease or even prevent illness. Canada has an emergency plan to ensure people will get vaccinated if a case of smallpox ever occurs in Canada.

More Information

Call Toronto Public Health at 416-338-7600 (TTY at 416-392-0658) or speak to your health care provider.