Smallpox is a contagious and potentially fatal infectious disease caused by a variola virus that emerged thousands of years ago in human populations. After a worldwide vaccination campaign, the disease has now been eliminated. The last case in the United States was in 1949 and the last naturally-occurring case in the world was in Somalia in 1977. There are still laboratory stockpiles of the virus which are kept as precautions for dealing with a potential smallpox outbreak as this disease could potentially be used as a bioterrorism agent.

There are two clinical forms of smallpox: variola major and variola minor. Variola major is the more severe and more common form and carries a 30 percent fatality rate. Variola minor is less common and carries a death rate of less than 1 percent.

Smallpox is reportable to the Iowa Department of Public Health by Iowa Administrative Code 641 IAC 1.


A person infected with smallpox will usually begin to notice signs and symptoms between 7 to 17 days following exposure. The disease process of smallpox is as follows:

Incubation period (time between exposure and initial signs of disease)

  • Usually lasts from 7 to 17 days with an average of 12 to 14 days
  • Infected individuals are not contagious during this time

Initial symptoms (prodrome phase)

  • Usually lasts between two to four days
  • Infected individuals are sometimes contagious during this stage
  • Symptoms usually include:
  • High fever (101-104 degrees Fahrenheit)
  • Malaise
  • Head and body aches
  • Vomiting (less common)

Early rash

  • Usually lasts about four days
  • Infected individuals are most contagious during this stage
  • The rash first emerges as small red spots on the tongue and in the mouth; these spots develop into sores that break open and spread large amounts of virus throughout the mouth and throat - this is when the infected person is most contagious
  • Around the time the sores in the mouth break down, a rash appears on the skin, beginning on the face and then spreading to the arms, legs, hands, and feet. The rash usually spreads throughout the entire body within 24 hours and at this point the fever typically decreases and the person begins to feel better
  • The rash becomes raised bumps by the third day
  • By the fourth day, the bumps fill with pus and often have a central depression that looks like a belly button (this is a distinguishing feature of smallpox). Fever will often rise again at this time and remain high until scabs form over the bumps

Pustular rash

  • Usually lasts about five days
  • Infected individuals continue to be contagious during this time
  • At this stage, the raised bumps become pustules which are sharply raised, round nodules that feel as though there are BBs under the skin

Pustules and scabs

  • Usually lasts about five days
  • Infected individuals continue to be contagious during this time
  • Pustules begin to form a crust and then scab over. By the end of the second week after the rash appears, most of the sores have scabbed over

Resolving scabs

  • Usually lasts about six days
  • Infected individuals continue to be contagious during this time
  • Scabs begin to fall off leaving marks on the skin that will eventually become pitted scars
  • By the end of the third week after the rash appears, most of the scabs will have fallen off

Scabs resolved

  • All of the scabs have fallen off
  • The person is no longer contagious

Smallpox lesions can be distinguished from chickenpox lesions because smallpox lesions develop at the same pace and appear identical while chickenpox lesions develop in successive crops. Also, the smallpox rash is typically most prominent on the face, arms, and legs while the chickenpox rash is usually most prominent on the trunk.


Smallpox is caused by a variola virus. In general, direct and fairly prolonged face-to-face contact is required to spread the disease from person to person. Less common ways to spread the disease include:

  • Direct contact with an infected individual’s bodily fluids
  • Direct contact with smallpox-contaminated objects such as bedding or clothing
  • Carried through the air in enclosed settings such as buildings, buses, and trains

Risk Factors

People who are in close contact with an infected person for prolonged periods of time are at an increased risk of contracting the disease. However, because the disease has been eliminated worldwide, the risk factors are quite low.


Routine vaccination for smallpox ended in 1972 because the vaccine was causing more disease than natural occurrences of the disease itself. It is no longer recommended to prevent disease in the public and therefore the vaccine is no longer routinely available. However, in the event that smallpox is released intentionally into the population, the United States has enough smallpox vaccine to vaccinate all Americans.


There is no proven treatment for smallpox. People suffering from the disease may benefit from supportive care such as intravenous fluids, antibiotics to control secondary infections, and medications to decrease fever or pain. Infected individuals must stay at home or in a healthcare facility until all scabs have fallen off and they are no longer contagious to prevent spread of the disease. This usually occurs within 21 to 28 days. If you suspect you are suffering from this disease or may have been exposed, contact your health care provider immediately.

Additional Resources