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.
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.
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:
 |
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.
|
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. |
| * Smallpox may be contagious during the prodrome
phase, but is most infectious during the first 7 to 10 days following
rash onset. |
