An infected corpse emerges from the permafrost: a grisly sight.
Courtesy Antony PranataFor those of us requiring a refresher, smallpox is an infection caused by the viruses variola major and variola minor, and is spread by coughing, sneezing, and transmission of bodily fluids. Extremely virulent, it has been found that smallpox infection can result from the inhalation of fewer than 10 viral particles. About one third of the people who contract v. major die, and those who survive often suffer from scarring, limb deformities, and blindness. Over the course of the 20th century alone, it is estimated that smallpox was responsible for at least 300 million deaths (possibly as many as 500 million) across the world.

Since as early as 1000 BC, people have attempted to combat the virus through inoculation, initially though methods like rubbing smallpox pus into skin lesions, or by inhaling ground up smallpox scabs (don’t judge—who here hasn’t snorted a scab or two in their day?). These techniques, called “variolation”, did in fact greatly reduce the mortality rate of those infected with smallpox, but it wasn’t until almost 1800 before the first true smallpox vaccination was created. Thanks to successful vaccination campaigns since then, in 1979 smallpox was announced to be, well, gone—it is the only human infectious disease that has been completely eradicated from nature.

So now we can go about our lives, playing Frisbee, painting by numbers, handling dead bodies, and squeezing pustules, with no fear of this horrible disease.

Though natural infections no longer occur, the smallpox virus itself is kind of a tenacious little creature, occasionally surviving for considerable lengths of time outside of a living body—a British construction worker, for instance, contracted the disease while demolishing a building that formerly housed smallpox victims, and Dutch researchers have found a living virus in a 13-year-old scab. The virus also tends to persist quite well when frozen, which brings us to the global warming issue.

When Europeans brought the disease to the Americas, native populations were devastated—smallpox killed them by the millions. Smallpox’s effect on Arctic groups was similar, and burying the bodies of victims in permafrost may have allowed for extremely long-term survival of the variola viruses.

This wouldn’t be a concern, except recently permafrost has shown itself to be a little less permanent than we’re used to. Global warming—which seems to be occurring more rapidly in the arctic—is thawing the permafrost, and exposing bodies that have been buried and preserved for hundreds of years. That some of these bodies very likely contain the smallpox virus has some people worried. A single encounter with the wrong corpse as it emerges from the permafrost could potentially result in an outbreak, and, having had no previous exposure to the virus, most of us would fare no better than the Native Americans did 400 years ago.

Not all knickers are twisted here, however. Some believe that the gradual thawing caused by global warming will actually reduce the chances of smallpox infection. The virus usually can’t survive being in a thawed body for more than a few days, so most infected bodies will lose their virulence before anyone is likely to encounter them. This depends on the type of permafrost, though—dry permafrost (as opposed to ice-rich permafrost) preserves bodies better, and would increase the chance of viral transmission, so never say never. And I never do.

Oh, wait.

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