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Smallpox Disease
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Incubation Period
(Duration: 7 to 17 days)
Not contagious
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Exposure
to the virus is followed by an incubation
period during
which people do not have any symptoms and may feel fine. This incubation
period averages about 12 to 14 days
but can range from 7 to 17 days. During this time,
people are not contagious.
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Initial Symptoms (Prodrome)
(Duration: 2 to 4 days)
Sometimes contagious*
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The first symptoms
of smallpox include fever, malaise,
head and body aches, and sometimes vomiting. The fever is usually high,
in the range of 101 to 104 degrees Fahrenheit. At this time, people are
usually too sick to carry on their normal activities. This is called the prodrome phase and may last for 2 to 4 days. * Smallpox may be contagious during the prodrome phase, but is most
infectious during the first 7 to 10 days following rash onset.
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Early Rash
(Duration: about 4 days)
Most contagious
Rash distribution:
View enlarged image.
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A rash emerges
first as small red spots on the
tongue and in the mouth.
These spots develop into sores that break open and
spread large amounts of the virus
into the mouth and throat. At this time, the person becomes most
contagious.
Around the time the sores in the mouth
break down, a rash appears on the
skin, starting on the face and 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. The rash is
centrifugally distributed – more lesions appear on extremities than on the
trunk. This is diagnostic for
smallpox and helps distinguish it from other diseases such as chickenpox
and measles
By the third day of the rash, the rash
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 bellybutton. (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.
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Pustular
Rash
(Duration: about 5 days)
Contagious
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The bumps become pustules—sharply raised, usually round and firm to the
touch as if there’s a small round object under the skin. People often say
the bumps feel like BB pellets embedded in the skin.
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Pustules
and Scabs
(Duration: about 5 days)
Contagious
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The pustules begin to
form a crust and then scab.
By the end of the second week after the rash
appears, most of the sores have scabbed over.
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Resolving
Scabs
(Duration: about 6 days)
Contagious
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The scabs begin to fall off, leaving
marks on the skin that eventually become pitted scars. Most scabs
will have fallen off three weeks after the rash appears.
The person is
contagious to others until all of the scabs have fallen off.
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Scabs
resolved
Not contagious
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Scabs have fallen off. Person
is no longer contagious.
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