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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.

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