Smallpox is a contagious
infection caused by the variola virus. Smallpox can be deadly, so if an
outbreak happens, it is vital to stay away from infected people. Get vaccinated
if you have been around someone who has smallpox. And if you have symptoms,
seek medical care.
The telltale signs of smallpox are severe
illness with a high fever, then a body rash. Symptoms appear about 12 days
after the person is infected.
Before there was a vaccine, smallpox
used to cause death all around the world. Thanks to widespread use of the
vaccine, the last natural case of smallpox occurred in 1977. And in 1980 the
World Health Organization (WHO) declared that the spread of smallpox was
stopped and that the disease had been wiped out.
Because there is a slight risk of serious reactions and
even death from the smallpox vaccine, routine smallpox immunization ended in
the United States in 1972.
Smallpox virus is known to exist in
labs at the Centers for Disease Control and Prevention (CDC) in the U.S. and at
the Institute of Virus Preparations in Siberia, Russia. But it may also be in
other labs. Some people worry that terrorists could release the virus and
spread smallpox to many people.
The first symptoms of
smallpox include a high fever, fatigue, a headache, and a backache. After 2 to 3 days of illness, a
flat, red rash appears. It usually starts on the face and upper arms, and then
it spreads all over your body. Over the next 2 to 3 weeks, the flat, red spots
become firm and dome-shaped and fill with pus. Then they scab over. Scabs fall
off 3 to 4 weeks after the rash first appears, and they leave pitted
incubation period for
smallpox is about 12 days. But symptoms can develop as
soon as 7 days or as long as 19 days after exposure.
You may mistake a severe
chickenpox rash for a smallpox rash at first. But
different viruses cause these illnesses and there are many
differences between chickenpox and smallpox rashes.
Smallpox is contagious. It
can be passed from one person to another through coughing, sneezing, or
breathing, or by contact with the scabs or the fluid from blisters. It can even
spread from an infected person's personal items and bedding. Smallpox is
easiest to spread during the first week of the rash. As scabs form, the person
is less contagious. But a person can spread the virus from the time the rash
first appears until all scabs have fallen off.
If a terrorist were
to release a small amount of the virus into the air, it is possible that it
could spread among a large number of people. The virus may be able to survive and infect
people for up to a day.
People who get this disease must
stay away from others to help prevent it from spreading. If there has been a
smallpox outbreak and you think you might have been exposed, call your doctor or local
health department. Do not go
directly to a health facility, because you could pass the disease to other
If a doctor suspected a case of smallpox, blood and skin tests would be needed to confirm the diagnosis. A confirmed case of smallpox
would be considered a worldwide health emergency. In the U.S., state and
federal health officials would quickly take action. They would keep anyone who
might have been exposed away from others.
If a smallpox outbreak
had been confirmed, a doctor in the outbreak area could diagnose smallpox
without a lab test. The doctor would look at the rash and ask about symptoms
and possible exposure to the disease.
There is no known cure for
smallpox. Treatment includes drinking plenty of fluids and taking medicines to
control pain and fever.
To prevent the spread of the virus, an
infected person must be kept away from other people until he or she is no
have survived smallpox cannot get it again.
Also, there is a
smallpox vaccine(What is a PDF document?). It has vaccinia virus in it, which is like the smallpox virus
but safer. If you get the shot before you've been exposed to smallpox, it will
likely protect you for at least 3 to 5 years. And having a second shot later
can protect you for an even longer period of time.
The shot works
even if you don't get it in advance. Most people who get the smallpox shot
within 3 days after they've been exposed to the virus will have no symptoms or
will have symptoms that aren't as severe. Getting a shot 4 to 7 days after
exposure may also help.1
People who have very close contact with a person who has gotten a smallpox vaccine can get an infection from the virus used in the vaccine. The infection usually causes a minor skin rash and is not smallpox. So the site where the smallpox vaccine was given should be covered until the scab falls off.
In the past,
when a smallpox infection was diagnosed, infected people were kept away from
others to prevent the spread of infection. Everyone who might have been exposed
to the virus was then vaccinated. This practice, called ring vaccination,
played a key role in wiping out smallpox. Many experts think it would be better
to carry out ring vaccination before mass vaccination if there were a case
Because there are risks of a serious reaction from the
vaccine, routine smallpox immunization doesn't occur. All children and most
adults in the U.S. today have a chance of getting infected if they are
exposed to the smallpox virus.
Since the September 2001 terrorist
attacks on the U.S., more vaccine has been made. The U.S. government has enough
smallpox vaccine for all Americans in case of an outbreak.1
The smallpox vaccine is recommended for laboratory workers who handle the vaccinia virus, for members of smallpox response teams, and for
certain people in the military. For accurate, up-to-date information, visit the Centers for Disease
Control and Prevention (CDC) website at www.bt.cdc.gov/agent/smallpox.
Learning about smallpox:
This Web site is intended to help people living in the
United States of America prepare for and respond to public health emergencies.
You can report an emergency, find information on the top emergency resources,
and learn practical tips such as how to assemble an emergency supply kit.
This Web site also has information on bioterrorism, chemical and
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and recent outbreaks and incidents.
The National Institute of Allergy and Infectious
Diseases conducts research and provides consumer information on infectious and
The World Health Organization (WHO) is an agency of the
United Nations. It has about 200 member states. WHO promotes technical
cooperation among nations on health issues, carries out programs to control and
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The Web site has information on many health topics, including health and
disease related to travel.
CitationsCenters for Disease Control and Prevention (2007). Smallpox fact sheet: Vaccine overview. Available online: http://emergency.cdc.gov/agent/smallpox/vaccination/facts.asp.Other Works ConsultedAmerican Academy of Pediatrics (2009). Smallpox (variola). In LK Pickering et al., eds., Red Book: 2009 Report of the Committee on Infectious Diseases, 28th ed., pp. 596–598. Elk Grove Village, IL: American Academy of Pediatrics.Centers for Disease Control and Prevention (2002). Annex 3: Guidelines for large scale smallpox vaccination clinics. Available online: http://www.bt.cdc.gov/agent/smallpox/response-plan/files/annex-3.pdf.Centers for Disease Control and Prevention (2007). Smallpox fact sheet: Smallpox overview. Available online: http://www.bt.cdc.gov/agent/smallpox/overview/disease-facts.asp.Cherry JD, Johnston S (2009). Smallpox (variola virus). In RD Feigin et al., eds., Feigin and Cherry's Textbook of Pediatric Infectious Diseases, 6th ed., pp. 2089–2101. Philadelphia: Saunders Elsevier.Damon IK (2010). Orthopoxviruses: Vaccinia (smallpox vaccine), variola (smallpox), monkeypox, and cowpox. In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 7th ed., vol. 2, pp. 1923–1932. Philadelphia: Churchill Livingstone Elsevier.Henderson DA, et al. (2008). Smallpox and vaccinia. In SA Plotkin et al., eds., Vaccines, 5th ed., pp.773–803. Philadelphia: Saunders Elsevier.Hirsch MS (2007). Measles, mumps, rubella, parvovirus, and poxvirus. In EG Nabel, ed., ACP Medicine, section 12, chap. 22. Hamilton, ON: BC Decker.Lane CH, Fauci AS (2012). Microbial bioterrorism. In DL Longo et al., eds., Harrison's Principles of Internal Medicine, 18th ed., vol. 1, pp. 1768–1778. New York: McGraw-Hill.Weiss MM, et al. (2004). Rethinking smallpox. Clinical Infectious Disease, 39(11): 1688–1673.
December 27, 2012
E. Gregory Thompson, MD - Internal Medicine & Christine Hahn, MD - Epidemiology
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