Smallpox is an acute infectious disease caused by a
virus. Smallpox infects only humans, and the last
naturally acquired case of smallpox in the world occurred in 1977.
Who gets smallpox?
No one has naturally contracted smallpox since 1977.
(There have been a limited number of cases since
1977 where researchers have become infected from
exposures that took place in a laboratory setting.)
When smallpox naturally occurred, the disease was
People became infected by:
Exposure to the respiratory secretions of people
Direct contact with smallpox
lesions of the skin and mucous membranes
Contact with items (e.g., bedding, clothing)
that been contaminated by such lesions or scabs.
People who developed a cough when they had
smallpox could spread the disease by coughing and
were considered at very high risk of transmitting the disease to others.
What were the symptoms of smallpox?
Symptoms in the initial stage of smallpox included:
Severe muscle aches
This stage would usually last for two
to four days and was, at times, accompanied by
flushing of the skin.
By the fourth day of illness, the
fever dropped and the characteristic smallpox rash
The rash started out as flat or slightly
thickened spots (known as macules) and quickly
progressed to raised spots (known as papules).
These papules continued to enlarge and became
filled with a clear fluid.
The lesions were then
referred to as vesicles.
The fluid in the vesicles would gradually change from clear to pus-like, and
the lesions were then referred to as pustules.
the pustule stage, a fever would again be common
and the pustules would start to form into scabs. Over time, the dried scab material would fall off of
This entire process took three to four weeks, and the areas affected by the rash were often permanently scarred.
There were two types of smallpox: variola major and
Variola major was the more severe
form and would usually kill 30-50 percent of persons
infected with it who were unvaccinated (3 percent of
those vaccinated), typically between the fifth and
seventh day of their illness.
Variola minor would
usually kill 1-2 percent of persons infected with it
who were unvaccinated.
There were also two rare
and more serious forms of smallpox.
severe form, is known as purpura variolosa or
The initial stage of the
illness (before the rash appeared) would be accompanied by a dark, purplish, blotchy flushing of
People who developed purpura variolosa
usually had a severe loss of blood into the skin and
internal organs (hemorrhage), and died before the
typical smallpox rash would appear.
About 3 percent
of those with variola major would develop purpura
Another rare and deadly form of smallpox
was referred to as flat-type smallpox that affected
about 5 percent of those with variola major.
with this form of the disease would have lesions that
developed more slowly, never raised above the
surface of the skin, and felt soft to the touch.
people with flat smallpox survived, they rarely
experienced severe scarring.
Both purpura variolosa
and flat smallpox were virtually never seen in persons infected with variola minor.
sometimes confused with chickenpox, but several
features of these diseases were significantly different:
The initial symptoms of smallpox were much
more severe than chickenpox i.e., high fever,
severe muscle aches, etc.
Smallpox rash was most common on exposed
portions of the body: face, forearms, wrists,
palms, lower legs, feet and soles.
most common on covered areas of the body.
Smallpox rash lesions tended to be at the same
state of development, and there was only one
eruption of pox lesions.
With chickenpox, it is
common to have more than one eruption of pox
lesions and the lesions may be in different stages
Smallpox lesions tended to be deeper in the skin
than chickenpox lesions, hard to the touch, and
the vesicles were tough to break.
How soon after exposure did symptoms
The first symptoms of smallpox usually occurred
within 10 to 12 days after exposure, with the rash
appearing two to four days later. The first symptoms could appear, however, as early as six days after
exposure, or as late as 22 days.
How was smallpox diagnosed?
Smallpox was often diagnosed based on the patient’s
clinical signs and symptoms; however, the disease
could be definitively diagnosed by isolation of the
virus from the blood or lesions, or by identification
of antibodies in the blood that were made in
response to the virus.
What was the treatment for smallpox?
There were no medicines available to treat smallpox
once the lesions began to develop.
medicines were sometimes useful at preventing the development of smallpox if they were given to a
person immediately after exposure to the disease.
Antibiotics might have been offered if the pustules of the rash appeared to be infected with a bacterium,
but supportive nursing care was the primary therapy
Vaccinia immune globulin (VIG) was used primarily
to treat complications of smallpox vaccination.
could also have been offered to persons exposed to
smallpox as a prophylaxis.
However, VIG needed to
be given before lesions began to develop, and it was
most effective when given with smallpox vaccination.
How was smallpox prevented (and ultimately
There is a vaccine to prevent smallpox that was
routinely administered in the United States until the
early 1970s. It is effective at preventing smallpox,
and was used to eradicate the disease.
The last case
of smallpox was diagnosed in Somalia in 1977. In
1980, the World Health Organization declared that smallpox had been eradicated from the face of the
While the smallpox vaccine is effective, it was
associated with a significant risk of adverse events in
vaccines. This risk of adverse events, accompanied by the rapid decrease in smallpox around the world
in the 1970s, was part of the justification for the U.S.
to discontinue routine vaccination against smallpox
before the disease was eradicated in 1977.
Very limited stockpiles of smallpox vaccine and VIG
are maintained by the Centers for Disease Control.
Routine vaccination of the civilian population for this disease is not recommended, nor is smallpox vaccination required for international travel to any country.
The only persons currently recommended to receive smallpox vaccine are persons working in a laboratory setting with smallpox or closely related viruses.
Where can I get more information?
Contact your physician or the Southern Nevada Health District, Office of Epidemiology at (702) 759-1300.