The U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick is the Army's chief facility for infectious disease research.

Research at the Maryland laboratory where Bruce E. Ivins allegedly developed a deadly strain of anthrax that killed five people in 2001 has been suspended after a spot check found samples of a dangerous pathogen that were not properly listed in its inventory.

Work was stopped at the laboratory last week after inspectors found four extra samples of Venezuelan equine encephalitis, The Washington Post's Nelson Hernandez reports. They discovered 20 samples of the pathogen in a box of vials instead of the 16 that had been listed in the institute's database, officials said.

In a memo obtained by the blog ScienceInsider, which first reported the breach in record-keeping, Col. John P. Skvorak attributed the undocumented pathogens to accounting errors, transcription errors or materials left behind by former employees (the latter of which was reiterated by unnamed sources to both The Post and The New York Times).

When such inventory problems occurred in the past "we either added it to the database or documented destruction, but overages now require submission of a Serious Incident Report, which goes to the Vice Chief of Staff of the Army," Skvorak wrote Feb. 4. "I believe that the probability that there are additional vials of BSAT not captured in our AIMS database is high," using the acronym for Biological Select Agents and Toxins.

Venezuelan equine encephalitis is a mosquito-borne pathogen that affects all types of equine animals, such as horses and donkeys, resulting in central nervous system disorders or death.

The disease can affect humans, resulting in flulike symptoms, according to the Centers for Disease Control. Those with weakened immune systems, such as the very young or the elderly, can become "severely ill or die from this disease."

A full-blown outbreak of VEE has not been seen in the United States since 1971 but surveillance activities of the disease has been stepped up ever since an outbreak was reported in 1993 in Chiapas, Mexico.

A "labor intensive" inventory of all of the lab's many thousands of research vials and specimens is expected to take months. The Fort Detrick lab conducts research on the world's deadliest pathogens, including the Ebola virus.

Meanwhile, the Justice Department and the Army institute at Fort Detrick are set to go to court with the widow of one of the anthrax victims, Florida tabloid photo editor Robert Stevens who was the first to die in 2001 when anthrax-laced letters were mailed anonymously to politicians and news media organizations.

His widow, Maureen Stevens, filed a wrongful-death lawsuit, alleging that the government failed to make sure that anthrax spores at the Fort Detrick lab were properly secured.