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.
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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
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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.
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Early Rash
(Duration: about 4 days)
Most contagious
Rash distribution:
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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.
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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* Smallpox may be contagious during the prodrome phase,
but is most infectious during the first 7 to 10 days following rash onset.
First Published: early-April, 2003
Updated: September 2003
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