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Centers for Disease Control and Prevention
1600 Clifton Rd.
Atlanta, GA 30333
USA
(404) 639-3311 |
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The
Disease
Smallpox is a serious, contagious, and sometimes fatal infectious
disease. There is no specific treatment for smallpox disease, and the only
prevention is vaccination. The name smallpox is derived from the
Latin word for “spotted” and refers to the raised bumps that appear on the
face and body of an infected person.
There are
two clinical forms of smallpox. Variola major is the severe and most common
form of smallpox, with a more extensive rash and higher fever. There are
four types of variola major smallpox: ordinary (the most frequent type,
accounting for 90% or more of cases); modified (mild and occurring in
previously vaccinated persons); flat; and hemorrhagic (both rare and very
severe). Historically, variola major has an overall fatality rate of about
30%; however, flat and hemorrhagic smallpox usually are fatal. Variola minor
is a less common presentation of smallpox, and a much less severe disease,
with death rates historically of 1% or less.
Smallpox
outbreaks have occurred from time to time for thousands of years, but the
disease is now eradicated after a successful worldwide vaccination program.
The last case of smallpox in the United States was in 1949. The last
naturally occurring case in the world was in Somalia in 1977. After the
disease was eliminated from the world, routine vaccination against smallpox
among the general public was stopped because it was no longer necessary for
prevention.
Where
Smallpox Comes From
Smallpox is caused by the variola virus that emerged in human
populations thousands of years ago. Except for laboratory stockpiles, the
variola virus has been eliminated. However, in the aftermath of the events
of September and October, 2001, there is heightened concern that the variola
virus might be used as an agent of bioterrorism. For this reason, the U.S.
government is taking precautions for dealing with a smallpox outbreak.
Transmission
Generally, direct and fairly prolonged face-to-face contact is required to
spread smallpox from one person to another. Smallpox also can be spread
through direct contact with infected bodily fluids or contaminated objects
such as bedding or clothing. Rarely, smallpox has been spread by virus
carried in the air in enclosed settings such as buildings, buses, and
trains. Humans are the only natural hosts of variola. Smallpox is not known
to be transmitted by insects or animals.
A person
with smallpox is sometimes contagious with onset of fever (prodrome phase),
but the person becomes most contagious with the onset of rash. At this stage
the infected person is usually very sick and not able to move around in the
community. The infected person is contagious until the last smallpox scab
falls off.
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Smallpox Disease |
Incubation Period
(Duration: 7 to 17 days)
Not contagious |
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. |
Initial Symptoms (Prodrome)
(Duration: 2 to 4 days)
Sometimes contagious* |
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. |
Early Rash
(Duration: about 4 days)
Most contagious
Rash
distribution:
View enlarged image. |
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.
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
|
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. |
Pustules and Scabs
(Duration: about 5 days)
Contagious
|
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. |
Resolving Scabs
(Duration: about 6 days)
Contagious |
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. |
Scabs resolved
Not contagious
|
Scabs
have fallen off. Person is no longer contagious. |
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* Smallpox
may be contagious during the prodrome phase, but is most infectious
during the first 7 to 10 days following rash onset.
For more about smallpox, see
Smallpox
Basics.
CDC public response hotline: |
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English: (888) 246-2675 |
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Español: (888) 246-2857 |
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TTY: (866) 874-2646 |
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