Smallpox is a viral infection. It is contagious and can be deadly. The disease was eliminated worldwide. This was done through global immunization programs. The last known natural occurring human case was in 1977. Governments have studied its use as a germ-warfare weapon. As a weapon, it would be released in the air. Those exposed could develop the disease. They would then pass it to other people.
Vaccination and Lymph System
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Variola major is the virus that causes the infection. It is spread:
The main risk factor for contracting smallpox is exposure to the virus in a laboratory or after its release during a biological terrorism attack.
Symptoms usually occur about 12 days after exposure. Hemorrhagic or malignant symptoms usually do not appear until death is near.
Early symptoms include:
Two to three days later:
Hemorrhagic symptoms include:
Malignant symptoms include:
The doctor will ask about your symptoms and medical history. A possible source of exposure will be looked for. A physical exam will be done.
Test may include:
No effective treatment for smallpox currently exists. Doctors can offer supportive care. Steps will be taken to prevent spread to others.
Fluids are given. The skin is kept clean. Medications can help control fever and pain. Antibiotics do not work against viruses. They may be given if other infections develop.
Cases are reported to public health officials. A person infected with smallpox should be kept isolated. This will help prevent the spread of infection.
In most cases, family members would provide care at home. Caregivers should:
Patients in the hospital will be placed in a special room. In some cases, forced quarantine may be necessary.
Many people were immunized prior to 1972. That protection has likely worn off or decreased. Routine vaccination is not recommended in the United States.
An emergency supply of the vaccine is kept. A vaccination within four days of exposure may prevent the disease. It can also make symptoms less severe. Anyone in close contact with a patient after the fever has started should receive the vaccine. Medical and emergency personnel also should be given the vaccine.
Two weeks or more could elapse before the first symptoms occur. The success of an attack would depend on the dose that was inhaled. Experts predict most of the released viruses could live in dry, cool air, without sunlight, for up to a day. Each person infected would likely pass the disease to 10 to 20 other people. Those people, in turn, could spread it to others. The fatality rate in naturally occurring smallpox is 30% or higher.
Centers for Disease Control and Prevention
National Library of Medicine
Public Health Agency of Canada
Breman JG, Henderson DA. Diagnosis and management of smallpox. N Engl J Med. 2002;25;346:1300-1308.
Dambro MR. Griffith's 5-Minute Clinical Consult. Philadelphia, PA: Lippincott Williams & Wilkins; 2001.
Mandell GL, Bennett JE, et al. Principles and Practice of Infectious Diseases. 6th ed. United Kingdom: Churchill Livingstone, Inc; 2004.
Smallpox. World Health Organization website. Available at:
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Working Group on Civilian Biodefense. Smallpox as a biological weapon: medical and public health management. JAMA. 1999;281:2127-2137.
Last reviewed June 2013 by Michael Woods, MD
Last Updated: 6/20/2013