The investigation at the U.S. Army Medical Research Institute of Infectious Diseases -- also known as USAMRIID -- was initiated Friday, said Debbie Wiereman, spokeswoman for the FBI's Washington Field Office.
"Only part of the facility is closed due to the activity," Wiereman told United Press International.
The Washington Field Office has been leading the FBI's efforts to find who sent the anthrax-laced letters that killed five people in the fall of 2001.
Neither Wiereman nor Chuck Dacey, a spokesman for Fort Detrick, would confirm the lab closures were specifically related to the "Amerithrax" investigation, as the anthrax case is designated. They declined to say how many labs were closed or give details about the nature of the effort underway.
The rest of the labs at the large campus, located about 50 miles from Washington, D.C., will continue operating, USAMRIID said in a statement.
"The temporary closing of laboratory suites is not associated with any incident that could pose a public or occupational health threat," the statement said. "Normal research operations will continue in the remainder of USAMRIID laboratories."
The complex has been both at the center of suspicion and a supporting player in the anthrax investigation from the beginning. Researchers at Fort Detrick helped analyze the fine powder found in the envelopes send via U.S. Mail to several destinations on the East Coast. Just over a year ago the FBI drained a pond near Fort Detrick in a search for clues in the case.
"The FBI has had a presence here since the fall of 2001," said Dacey.
USAMRIID also is the former employer of Dr. Stephen Hatfill, a bioweapons expert and researcher named as a "person of interest" in the investigation by U.S. Attorney General John Ashcroft. Hatfill has since sued Ashcroft and the Justice Department for linking him to the case. Hatfill's lawsuit was put off until October based on FBI assertions that proceeding with the case would compromise the investigation.
Hatfill also recently filed a suit against New York Times columnist Nicholas Kristof alleging he recklessly named Hatfill as the source of the anthrax letters.
How the current activity might be linked to Hatfill, or to some other line of the anthrax investigation, is unclear. The anthrax in the envelopes has been widely reported to have come from strains studied in the United States and to be particularly sophisticated. The size of the particles was reduced so that it would better penetrate the lung tissue. It was also processed to enable it to stay suspended in the air for extended periods making it more likely to be inhaled.
The processing made the white powder so deadly that at least four of the five casualties -- two postal workers, a hospital employee in New York and an elderly woman in Connecticut -- appear to be the indirect victims of cross contamination. Powder leaked from the envelopes onto postal processing machines and contaminated other letters in the mail flow. Altogether, the letters sickened 22 people, including an infant. Many contracted serious, though less-than-lethal, skin infections from the spores.
The source of the anthrax that killed the first victim, photo editor Bob Stevens of Boca Raton, Fla., has not been found.
Fort Detrick has long been involved with biowarfare. Scientists there began developing bioweapons and countermeasures in 1943. President Richard M. Nixon ordered a halt to the weapons research in 1969.
At least one other facility has studied weaponized anthrax. The Army's Dugway Proving Grounds, located roughly 85 miles southwest of Salt Lake City, tests military equipment against biological and chemical weapons. Officials there acknowledged at the end of 2001 that their researchers produced dried anthrax for use in Dugway tests.
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