Smallpox is a contagious viral infection that can be deadly. The disease was eliminated worldwide by 1980 through global immunization programs. Although 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 and pass it to other people.

Vaccination and Lymph System


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Variola major virus causes the infection. It is spread through airborne droplets of infected saliva. The virus passes between people who have direct contact. Handling contaminated bed linens or clothing also can cause the disease. Two rare, more serious types of the disease are hemorrhagic and malignant, which are transmitted the same way.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. The main risk factor for contracting smallpox is exposure to the virus 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:

  • High fever
  • Fatigue
  • Severe headache
  • Backache
  • Possible stomach pain or delirium
  • Fatigue
  • Sore throat
  • Nausea and vomiting

Two to three days later:

  • Rash appears on the mouth, throat, face, and arms, then spreads to the legs and trunk
  • Red, flat lesions
  • Lesions appear at the same time
  • Lesions fill with fluid, then pus
  • Crusts form during the second week
  • Scabs form and fall off after 3 to 4 weeks

Hemorrhagic symptoms include:

  • High fever
  • Fatigue
  • Headache
  • Backache
  • Possible stomach pain
  • Dark red coloration
  • Bleeding into the skin and mucus membranes

Malignant symptoms include:

  • High fever
  • Fatigue
  • Headache
  • Backache
  • Slowly developing lesions that remain soft and flat
  • Skin looks like reddish-colored crepe rubber
  • Large amounts of skin may peel, if the patient survives


The doctor will ask about your symptoms, medical history, and possible source of exposure, and perform a physical exam. Other cases in the area may alert healthcare workers of the possibility of a bioterrorism attack.

Test may include:

  • Examination of saliva and fluid from skin lesions under a microscope
  • Taking a sample (a culture) of saliva and fluid from skin lesions to check for bacteria
  • Blood test to detect antibodies to smallpox


No effective treatment for smallpox currently exists. Doctors can offer supportive care and take steps to prevent spread to others.

Supportive Care

Fluids are given, and the skin is kept clean. Medications can help control fever and pain. Antibiotics may be given if other infections develop.

Public Health Measures

Cases are reported to public health officials. To prevent the spread of infection, a patient should be kept isolated from other people. In most cases, family members would care for the patient at home. Caregivers should be vaccinated and wear a mask, gloves, goggles, and a gown. Clothing, bed linens, and surfaces should be disinfected. Patients in the hospital should be placed in a room with a special ventilation system. Officials may need to designate specific hospitals to provide only smallpox care. Forced quarantine may be necessary in some cases.


Many people were immunized prior to 1972. But that protection likely has worn off or decreased. Routine vaccination is not recommended. The United States government maintains an emergency vaccine supply. Vaccination within four days of exposure may prevent the disease or 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.

There would be no warning systems to alert authorities that the virus has been released. Two weeks or more could elapse before the first symptoms occurred and were diagnosed as smallpox. 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

The Johns Hopkins Center for Public Health Preparedness (JHCPHP)


Ontario Ministry of Health and Long-term Care

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, Dolin R. Principles and Practice of Infectious Diseases . 6th ed. United Kingdom: Churchill Livingstone, Inc; 2004.

Smallpox. World Health Organization website. Available at: .

Working Group on Civilian Biodefense. Smallpox as a biological weapon: medical and public health management. JAMA . 1999;281:2127-2137.

Last reviewed November 2007 by David L. Horn, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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