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May 15, 2014 | By:  Julia Paoli
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Smallpox: The Most Talked About Eradicated Disease

This week Kriti from Microbe Matters and I are teaming up to cover Smallpox because of a paper published on May 1st regarding what to do with the remaining smallpox stockpiles. I will be focusing on the background and history of the virus, while Kriti will discuss the differing viewpoints on the preservation of the smallpox samples.

Smallpox is unique in that it's the only infectious disease to have ever been eradicated. The disease is caused by the variola virus, which is closely related to the cowpox virus. Smallpox has been recorded in the human population for over 3,000 years. To put that in perspective the city of Rome was founded just shy of 3,000 years ago in 753 BC. The last natural case of smallpox occurred in Somalia in 1977, and since then there have only ever been accidental exposures to smallpox in a laboratory setting.

Until its eradication in 1979, smallpox was "one of the world's most feared diseases," and rightly so. The disease has a relatively high fatality rate of 30% percent. Smallpox derives its name from the raised bumps it causes on the body of an infected person. A few days after the initial infection, the bumps develop into fluid-filled lesions and then into painful, pus-filled ones. Scabs form over the lesions leaving survivors with pitted scars.

The process of eradicating smallpox was long and complicated, requiring the coordinated efforts of people around the globe. Not every disease can be eradicated; it just so happened that smallpox has many characteristics that lend ease to eradication. The incubation period, the time between initial infection and visible symptoms, is relatively short, which prevents the disease from spreading undetected. The symptoms are also very distinctive, allowing for easy identification of smallpox patients. The World Health Organization put in place a "ring vaccination" method whereby vaccines weren't given only to infected people, but also to anyone who may have been exposed to an infected person. "Ring vaccination" effectively hindered the mass spread of smallpox since officials were able to isolate and treat affected areas early. In remote areas, World Health Organization workers tracked down infected persons by showing locals pictures of people with smallpox symptoms and asking if they had seen anyone with them.

Luckily for humans, smallpox only infects us. The lack of of an animal reservoir really aided in eradicating the disease. A large number of diseases affecting humans can be caught and transmitted by other species. For example, Dengue Fever is spread by infected

mosquitoes, while the Black Plague was spread by fleas on rats. Even if all humans were somehow vaccinated against Dengue Fever, the virus would still not be eradicated since it would still survive in the mosquito population. Since smallpox only infects us, once the human population was vaccinated the virus was wiped out.

Effective vaccination also helped in the eradication process. The smallpox vaccine can prevent infection up to four days after initial exposure. The vaccine itself does not contain any of the variola virus but a related one called vaccinia. In 1796 Edward Jenner, the pioneer of the smallpox vaccine, carried out his famous experiment. Folklore claimed that milkmaids were immune to smallpox. Jenner tested this lore by exposing an eight year old boy to cowpox. Sure enough, further tests showed the boy to be immune to smallpox. Unlike malaria, once a person has been infected with smallpox and survived, he or she is immune to all further infections. Six other diseases have been identified as possible candidates for eradication by the Carter Center International Task Force for Disease Eradication: Guinea worm (dracunculiasis), poliomyelitis, mumps, rubella, lymphatic filariasis, cysticercosis, and measles. Scientists and international organizations are working with the Task Force to try and eliminate these diseases.

Even though smallpox was officially eradicated, two stockpiles of the variola virus remain in the world. Both the CDC, located in the state of Georgia, and a state laboratory in Russia have supplies of the virus. In 1990, a World Health Organization advisory committee "recommended destroying" the remaining viruses. However since then, the US and Russia have been able to push back deadlines requiring smallpox's destruction. In a few weeks, though, the World Health Assembly will meet in Geneva to discuss smallpox eradication. Check out my friend Kriti's blog for more about the elimination of remaining smallpox samples.


Frequently asked questions and answers on smallpox. WHO (2014).

The History of Vaccines. The College of Physicians of Philadelphia (2014).

Disease Eradication. The College of Physicians of Philadelphia (2014).

Barnes, D. "Key U.S. Scientist Pushes to Hang Onto Last Remaining Smallpox Virus." National Journal. May 2, 2014.

Smallpox. CDC (2014).


Barbra Rice (via CDC).

Sanofi Pasteur (via Flickr).

1 Comment
June 09, 2014 | 05:12 PM
Posted By:  Ting Yung
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