Laci Green examines some of history's most horrifying and death-dealing illnesses, the kind that lay waste to entire populations.
The Centers for Disease Control and Prevention is now running tests on six forgotten vials of smallpox recently discovered in an unsecured laboratory.
Even though smallpox has been eradicated, the world's remaining stockpiles should not be destroyed, scientists said.
Only two diseases in the world have ever been declared "eradicated." And of those two, only one affects humans. That disease is smallpox. Trace explains how the smallpox eradication effort worked, and how it might be applied to other illnesses.