The prick of a needle, the slip of a scalpel -- routine accidents in any hospital or medical lab.
But for the scientists who work with nature's deadliest germs, handling razor-sharp instruments in the clumsy spacesuits of the nation's highest-security biodefense research centers, momentary mistakes are the stuff of nightmares.
In a Fort Detrick isolation unit known as "the slammer," a young virologist is in the 10th day of a watch for symptoms of Ebola, a highly contagious disease in which headache and fever can swiftly progress to uncontrollable bleeding and death. It's the first time the slammer has been occupied since 1985.
The researcher grazed her hand with a needle Feb. 11 while testing treatments on Ebola-infected mice. Officials at the U.S. Army Medical Research Institute of Infectious Diseases sent her home overnight to pack her things -- the disease is not transmissible in the first day after exposure -- and then checked her into the Patient Isolation Suite for a stay of up to 30 days.
The suite on the Frederick Army post, two hospital-style rooms and a treatment area, is called "the slammer" both for its jail-like status and for the noise made by the doors that seal it off from the outside world.
Air passes in and out of the suite through filters fine enough to catch virus particles, and a disinfecting shower prevents visitors from carrying germs outside.
The virologist, a postdoctoral fellow who has worked at USAMRIID since 2002, appears to be fine so far, officials say. But given the incubation period of Ebola hemorrhagic fever, made infamous by Richard Preston's 1994 best-seller The Hot Zone, they cannot be certain for another week or longer that she will avoid getting sick.
"So far, all the tests are absolutely negative," said Dr. Peter B. Jahrling, principal scientific adviser at USAMRIID. Under the circumstances, he added, "She seems to be holding up pretty well."
"It's great that she's at day nine with no symptoms," said David R. Franz, a former USAMRIID commander who now works at Midwest Research Institute in Frederick. "I would be nervous for the first few days. But I'd feel better with every day that passes."
Cooped up in the slammer, the virologist has a computer, television and VCR to pass the time. Doctors stop by to take blood samples or conduct tests, and fellow scientists visit to keep her company. Because she has no symptoms of illness, visitors can dress in medical masks and gowns rather than full biosafety suits, officials say.
When the accident occurred, the researcher was holding an anesthetized mouse in her hand while injecting it in the stomach with a syringe, Jahrling said. She was wearing a surgical glove with the biosafety suit on top, he said.
"There's always a tradeoff between safety and manual dexterity," said Jahrling, a virologist who has worked with Ebola, smallpox and other germs for three decades. "You want protection, but you don't want to work with mittens on." He added: "Needle-sticks are always what scare me most."
The scientist in the slammer, whose identity is being withheld by the Army at her request, is one of a growing number of bioscientists working with exotic pathogens.
Funding for such work has ballooned since the Sept. 11 and anthrax attacks of 2001, with billions in new federal research dollars pouring into university and government labs as researchers hunt for new vaccines and drugs.
Federal safety standards require top-security Biosafety Level 4 facilities for work with "dangerous and exotic agents" that pose "a high risk of aerosol transmission and life-threatening disease." Only a handful of pathogens require such stringent controls, including full biosafety suits with filtered air supplied by hose, decontaminating showers and negative air pressure to prevent escaping germs.
USAMRIID has one of four BSL-4 labs in the country. But at least six more are planned, including two more at Fort Detrick to be operated by the National Institutes of Health and the Department of Homeland Security as part of a "national biodefense campus."
USAMRIID's official mission is to safeguard U.S. troops, and Ebola has been on the Defense Intelligence Agency's threat list for years.
Soviet bioweapons experts studied Ebola and weaponized a close cousin, the Marburg virus. One Soviet scientist died in 1988 after accidentally pricking his thumb with a Marburg-loaded syringe, according to Soviet defector Ken Alibek, who told the story in his 1999 memoir Biohazard.
The Japanese sect Aum Shin Rikyo, which carried out a poison gas attack on the Tokyo subway in 1995, dispatched members to Zaire during an Ebola outbreak, apparently with the idea of collecting the virus, though nothing came of it.
Over the past few years, a USAMRIID research team led by Thomas W. Geisbert has made significant progress in developing vaccines and treatments for Ebola.
The virologist who treated the mouse this month is the 13th patient admitted to the slammer since it opened in 1972, according to USAMRIID.
The previous 12 had possible exposure to deadly viruses, six by skin puncture and six by inhalation. None developed any disease.
But three workers in the now-defunct offensive bioweapons program at Fort Detrick died of accidental infections in the 1950s. And despite the facility's recent safety record, working with lethal germs can be daunting, particularly for young researchers.
Jahrling recounted his first experience in a BSL-4 lab at USAMRIID 30 years ago, when he had to extract Lassa fever virus from a sealed glass tube by snapping it in two -- a technique that scientists have abandoned.
"You're holding this busted glass tube with enough virus in it to kill you hundreds of times over," said Jahrling. "I remember thinking, 'What the hell am I doing here?'"