An outbreak of smallpox was the farthest thing from Paul Levengood's mind when his staff at the Virginia Historical Society put together an exhibit of "bizarre bits" in the society's collection since its founding in 1831.
There was Confederate President Jefferson Davis's cigar, confiscated by Union troops. There was a fungus carving of Robert E. Lee on his horse Traveller and a wreath made of human hair.
Then someone mentioned a letter, handwritten and dated 1876, with what appeared to be a smallpox scab pinned inside—light brown, about the size of a pencil eraser, and crumbling.
"It attracted a good deal of notice when people came to the exhibit," says Dr. Levengood, the historian who is president and chief executive officer of the VHS.
The scab also got the attention of the Centers for Disease Control and Prevention, home to one of the world's two known caches of live smallpox virus. Alerted by a government scientist in Maryland who was concerned that the scab might transmit infection, the agency dispatched two CDC representatives to Richmond in March. They donned disposable surgical gowns and gloves, lifted the scab from a display case, sealed it in bio-bags inside a red cooler, and whisked it back to a high-security lab deep within the CDC's Atlanta headquarters.
The historians were surprised. They had thought it was merely a "weird thing," Dr. Levengood says.
The CDC says it was just following rules. "We really did not know what this was," says Andrea McCollum, one of the two disease detectives who retrieved and drove the scab back to Atlanta in the trunk of their car. "There was a public-health concern that this scab could be infectious."
A World Health Organization assembly this week is discussing whether to set a date to destroy the stocks of infectious smallpox held by the CDC and a Russian government laboratory. But nobody truly knows how much smallpox virus may be lurking in archives or cemeteries—since the deadly disease was declared eradicated in 1980.
U.S. officials fear that terrorists hold stocks of the virus that could be unleashed in a bioterror attack. Long-forgotten vials of virus have been found from time to time in the freezers of virologists, even though only the CDC and the Russian lab, known as Vector, have been authorized by the WHO since 1984 to hold stocks of live virus.
Then there are the relics. To smallpox scientists, they are archaeological finds that, like fossils, can shed light today on ways to combat an eradicated disease that they fear could return.
Over roughly the past decade, the CDC has been called to retrieve the remains of a man covered with smallpox lesions whose coffin was unearthed during construction near Louisville, Ky., as well as suspicious-looking scabs in a library book in New Mexico and a museum in Arkansas, says Inger Damon, chief of the CDC's poxvirus and rabies branch.
Peter Jahrling, director of a biodefense research facility at the National Institute of Allergy and Infectious Diseases, was once given a smallpox-scabbed infant's arm, preserved in formaldehyde in a large jar.
Scabs—pieces of dessicated skin, white blood cells, virus and other material—were used in the 19th century to vaccinate people against smallpox. They were inserted into small breaks in the skin, prompting the body to build an immune response.
The scab the CDC retrieved in March was mailed from a son to his father. "Dear Pa…the piece I inclose is perfectly fresh and was taken from an infant's arm yesterday…" read the letter. "Dr. Harris says the inclosed scab will vaccinate 12 persons, but if you want more, you must send for it. I will pin this to the letter so that you cannot lose it as you did before."
Museum officials say they weren't worried about infection. A medical historian had told them years ago that old scabs degrade. "Our strong assumption was that it was not a danger," Dr. Levengood says. Staff members, wearing gloves, encased the scab in mylar and placed it in a plexiglass display case for the exhibit, which opened in June 2010.
But Nick Radonic, an electrical engineer from Derwood, Md., was alarmed when he read a newspaper review in February that mentioned the scab. He emailed the museum, which assured him the item was contained. Unconvinced, he next emailed a neighbor, a doctor and mathematician at the National Institutes of Health, asking what to do.
"If it really contained smallpox virus that happened to be viable, the downside of release would have been enormous," Mr. Radonic says.
The neighbor, John Spouge, consulted virologists. "I'd put it in the autoclave myself. Who needs the chance?" one responded, citing a standard method of inactivating viruses with heat and pressure.
Finally, Dr. Spouge reached Dr. Jahrling, who put him in touch with the CDC.
Scabs can remain infectious for decades if kept under the right conditions, but the CDC says that most of those it has found have deteriorated.
When they retrieved the scab, Dr. McCollum and a CDC colleague, both immunized against smallpox, assured VHS staff that the chances of infection appeared low.
The two locked the scab in the trunk of their car and drove straight to Atlanta, a nine-hour trip.
Clad in pressurized moonsuits in the high-security, BSL-4 lab, CDC microbiologists determined within a few hours that the scab contains virus from the smallpox vaccine but didn't contain the deadly disease virus itself. They have since moved the scab, which they have irradiated, to a medium-security lab.
Still, the CDC researchers aren't disappointed. No one knows precisely which viruses were used in vaccines historically in the U.S., and the scab, with relatively well preserved DNA, could help shed light on that, Dr. Damon says.
The CDC plans to return the scab to the VHS. It's probably not the last such artifact that will emerge, given the number of old medicine chests and other medical relics that abound, says Lee Shepard, the museum's vice president for collections. "There are probably a good number of these things out there," he says.