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Scientific Procedures in Anthrax Probe Detailed

Scientific analysts involved in a federal probe of the 2001 anthrax mailings in a report published on Tuesday detailed the genomic methods that led investigators to attribute the deadly attacks to a U.S. Army microbiologist, the Center for Disease Research and Policy reported (see GSN, Feb. 18).

The FBI ultimately pinned the mailings on microbiologist Bruce Ivins, who took his life in July 2008 before charges were filed against him. Federal investigators ended their probe last year, but some U.S. lawmakers have continued to question the scientific reasoning supporting the assertion that Ivins had carried out the mailings, which killed five people.

The probe displayed the importance of sequencing entire genomes in microbial forensic investigations, though the technique may not be appropriate for all infectious agents that do not form spores, the researchers wrote in the report published by the Proceedings of the National Academy of Sciences.

Prior to the FBI investigation into the 2001 mailings, only small segments of genetic sequences were subjected to microbial forensics, the report says.

"The accuracy and reliability of whole-genome sequencing as a microbial forensic technique was not appreciated before the initiation of this project," wrote the scientists from the FBI, Northern Arizona University, the University of Maryland, and the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick, Md.

Scientists supporting the probe grew cultures using spores taken from the envelopes received by U.S. senators and several media organizations. Those cultures resulted in a variety of colonies with differing physical characteristics. A minority of the cultures displayed mutations from the Bacillus anthracis Ames variety contained in the letters, the report states.

The confirmed mutations were contrasted with Bacillus anthracis Ames variety samples taken by federal investigators from laboratories in various countries. Eight of the 947 collected samples contained each of the four mutations found in the spores from the mailings. All of those eight Ames strains could be traced back to the anthrax supply controlled by Ivins, according to a previously-published National Research Council report (Center for Infectious Disease Research and Policy release, March 8).

NTI Analysis