Smallpox is an infection caused by the variola virus, a member of the poxvirus family. The disease is highly infectious. Passage from person to person via contaminated aerosolized droplets (from sneezing, for example) occurs easily, and so the spread of smallpox through a population can occur quickly. Like most viruses and other microorganisms, the variola virus can be transported from one location to another without difficulty, thus making smallpox a potentially attractive choice for biological warfare and a serious threat as a weapon of bioterrorists.

Smallpox is a highly contagious disease. The virus can spread by direct contact with those who are infected, in contaminated air droplets, and even by touching objects such as books and blankets that have been previously used by someone who has smallpox.

When infected with the virus, there is a 12–14 day symptom-free period, during which the virus is multiplying in the body. There is then a sudden onset of symptoms. The symptoms include fever and chills, muscle aches, and a flat, reddish-purple rash on the chest, abdomen, and back. These symptoms last about three days, after which the rash fades and the fever drops. A day or two later, the fever returns, along with a bumpy rash starting on the feet, hands, and face. This rash progresses from the feet along the legs, from the hands along the arms, and from the face down the neck, ultimately reaching and including the chest, abdomen, and back. The individual bumps, or papules, fill with clear fluid, and, over the course of 10–12 days, became pus-filled. The pox eventually scabs over, and when the scab falls off it leaves behind a pock-mark or pit, which remains as a permanent scar on the skin of the victim.

Smallpox can be lethal, usually due to bacterial infection of the open skin lesions, pneumonia, or bone infections. A severe and quickly fatal form of smallpox is known as "sledgehammer smallpox." This form of smallpox is characterized by bleeding from the skin lesions, as well as from the mouth, nose, and other areas of the body.

Smallpox has been present for thousands of years. For example, studies of the mummy of Pharaoh Ramses V, who died in 1157 B.C. , revealed symptoms of smallpox infection.

Large smallpox epidemics have occurred throughout recorded history. Attempts to protect against smallpox infection began centuries ago, even thought the microbiological nature of the disease was then unknown. In the tenth century, accounts from China, India, and the Americas describe how individuals who had even a mild case of smallpox could not be infected again. Fluid or pus from the skin lesions was scratched into the skin of those who had never had the illness, in an attempt to produce a mild reaction and its accompanying protective effect. Unfortunately, these efforts sometimes resulted in full-fledged smallpox, and helped spread the infection. Such crude vaccinations against smallpox were outlawed in Colonial America.

In 1798, Edward Jenner published his observation that milkmaids who contracted cowpox infection caused by vaccinia virus (a relative of variola) were immune to smallpox. He used infected material from the cowpox lesions to prepare an injection that helped protect the humans. Although Jenner's development of immunization was harshly criticized at first, the work paved the way for the development of vaccines.

Until the development of a smallpox vaccine, no treatment for smallpox was known, nor could anything shorten the course of the disease. Until its eradication, smallpox was diagnosed most clearly from the patients' symptoms. Electron microscopic studies could identify the variola virus in fluid isolated from disease papules, from infected urine, or from the blood prior to the appearance of the papular rash.

In the 1960s, the World Health organization (WHO) began a campaign to treat people infected with smallpox and vaccinate those who might be exposed to the infection. The WHO program was extremely successful, and the virus was declared eradicated worldwide in May of 1980. Stored stocks of the virus were maintained in two laboratories. One is housed at the Centers for Disease Control and Prevention in Atlanta, Georgia. The other smallpox stock is maintained in Russia.

These stocks were slated to be destroyed in the late 1990s however, U.S. President William J. Clinton halted plans for destruction of the American stocks. Concern that another poxvirus could mutate (undergo genetic changes) and cause human infection, along with the possible use of smallpox as a bioterrorist weapon or as a weapon of stateanctioned war, has made preservation of the smallpox stock for vaccine development purposes important. As of early 2003, the stocks remain undisturbed.



Hopkins, D. R. The Greatest Killer: Smallpox in History. Chicago: University of Chicago Press, 2002.

Preston, R. The Demon in the Freezer. New York: Random House, 2002.


Henderson, D. A., T. V. Inglesby, J. G. Bartlett, et al. "Smallpox as a Biological Weapon: Medical and Public Health Management." Journal of the American Medical Association no. 281 (1999): 2127–137.


Centers for Diseases Control and Prevention. "Smallpox." Public Health Emergency Preparedness and Response. November 26, 2002. < > (27 November 2002).


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