One to two weeks after initial exposure to the smallpox virus, signs and symptoms of the disease typically appear. Early smallpox symptoms are often difficult to diagnose because they are similar to symptoms of the flu. Common symptoms may include high fever, body aches, and vomiting.
Symptoms of smallpox usually appear within 7 to 17 days after transmission of the smallpox virus (variola). This period between smallpox transmission and symptoms is called the smallpox incubation period. During this time, the smallpox virus is multiplying inside of the body.
Once symptoms begin, the first smallpox symptoms may be hard to distinguish from the symptoms of other flu-like illnesses. Early symptoms can include:
- High fever
- Body aches
At this time, people are usually too sick to carry on their normal activities. This is called the prodrome phase, and it may last for two to four days. A person is somewhat contagious during this period (people are most contagious during the first seven to ten days following appearance of a rash).
After a couple of days, a person with smallpox symptoms will begin to develop a smallpox rash. Over the next couple of weeks, this rash will go through various stages, including:
- Early rash
- Pustular rash
- Pustules and scabs
- Resolving scabs
- Scabs resolved.
A rash emerges first as small red spots on the tongue and in the mouth. These spots develop into sores that break open, and large amounts of the virus are spread into the mouth and throat. At this time, the person becomes highly contagious.
Around the time the sores in the mouth break down, a rash appears on the skin, starting on the face, spreading to the arms and legs, and then to the hands and feet. Usually, the rash spreads to all parts of the body within 24 hours. As the rash appears, the fever usually falls and the person may start to feel better.
By the third day of the rash, it becomes raised bumps. By the fourth day, the bumps fill with a thick, opaque fluid and often have a depression in the center that looks like a belly button (this is a major distinguishing characteristic of smallpox).
Fever often will rise again at this time and remain high until scabs form over the bumps.