about Epidemiology & the department

Epidemiology academic information

Epidemiology faculty

Epidemilogy resources

sites of interest to Epidemiology professionals

Last Updated

13 Jul 2003

Source: Washington Post, May 10, 2002.

Clues to Anthrax Attacks Found

Findings of DNA Analysis Could Point to Source of Microbes

By Rick Weiss, Washington Post Staff Writer

The first detailed genetic analysis of the bacteria used in last fall's anthrax attacks has revealed minuscule but consistent differences between the terrorist strain and the nearly identical strain developed by the Army at Fort Detrick -- clues that could narrow the search for the person or people behind the attacks.

The differences -- a handful of mutations that apparently arose some time after the bacteria left the Army lab -- are so subtle that it is now indisputable the mailed microbes are direct descendants of the germs developed at Fort Detrick, according to scientists who did the analysis.

But the tiny genetic hallmarks found in the DNA of the bioterror microbes also amount to telltale fingerprints that had been invisible to scientists, who until now had been relying on cruder genetic techniques.

Those fingerprints could eventually help investigators figure out which of the 20 or so laboratories known to have worked with the Army's strain was the one the terrorist's microbes came from.

Researchers cautioned yesterday that they could not be certain that genetic fingerprinting would solve the mystery of who mailed the deadly bacterial spores to media organizations and elected officials last fall, killing five and sickening at least 13. Even if the technique helps to identify the lab from which the microbes most likely came, there will still be questions about who absconded with them and to whom that person may have passed them along.

Indeed, some scientists said yesterday they were discouraged that the differences between the bioterror and Army strains are so small because that finding makes it more likely that rare but unavoidable errors in the fingerprinting process could obscure the similarly rare differences between substrains.

But project leaders Timothy Read and Claire Fraser of the Institute for Genomic Research (TIGR) in Rockville said they hope the detailed genetic information would help rule out certain labs as sources of the terrorist bugs and perhaps highlight others for the FBI.

"Without a doubt, this kind of information can lead you in the right direction," said Fraser, who is president of TIGR, a not-for-profit research institute. "It has the potential to narrow the focus a lot."

The FBI has said that it has no hot leads in the case. FBI Director Robert S. Mueller III said in Senate testimony on Wednesday that recent scientific findings in the case have not altered the belief that the culprit is likely a U.S. man with a scientific background, acting alone. Lately, the agency has been giving lie-detector tests to some scientists with a history in the field.

More generally, several scientists said, the new work shows that the novel DNA analysis techniques developed by TIGR and Paul Keim of Northern Arizona University can reliably identify small but important differences among closely related strains of bacteria. That could help researchers identify the small genetic variations that account for the differences in virulence and antibiotic resistance among strains. It could also speed the development of new medicines, vaccines and detection systems.

To achieve those goals, researchers are recommending a crash program to conduct similar studies on many disease-causing bacteria, especially those most likely to be used in terrorist attacks.

"Building a comprehensive database of . . . the genomes of important pathogens will allow investigators to quickly pinpoint the isolate that is most closely related to an outbreak strain," the researchers conclude in today's issue of the journal Science. "Such a database would greatly accelerate investigations and may deter future attacks."

The new work grew out of a 3-year-old effort at TIGR to determine the order of all 5.2 million molecular "letters" of genetic code inside Bacillus anthracis, the bacterium that causes anthrax. That federally funded project focused on a sample of the Ames strain obtained from Porton Down, a British biological warfare lab, which in turn had obtained the microbes from Fort Detrick.

The work was still incomplete when anthrax spores started turning up in U.S. letters last fall. Preliminary tests on a few key segments of DNA in those spores indicated that the bacteria, like those from Detrick, belonged to the Ames strain, a lineage that had its start in an anthrax-infected Texas cow. Bacteria from that cow were sent in 1981 to Detrick, where the strain was for years a central player in this nation's biological warfare program. Offspring of those microbes were later distributed to as many as 20 laboratories in the United States and abroad, including Porton Down.

One of the U.S. government's first responses to the mail attacks was to direct grant money to TIGR and Keim to speed the completion of the Porton Down/Detrick sequencing project and to determine the full genetic sequence of the anthrax bacteria retrieved from Bob Stevens (case 5), the Florida photo editor who was the first to die in last fall's attacks.

Today's report shows that virtually every clearly identifiable letter of genetic code is identical in both of those Ames samples. But it also notes four locations where there were small but consistent differences between the two.

Scientists said it is impossible to say when those differences arose. Little is known about the rate with which mutations typically arise in B. anthracis, and even less is known about how those rates might change during the months or years that the bacteria can lay dormant in their spore form.

Without that kind of information, it's not possible to calculate whether the terrorist substrain came out of Detrick's labs only recently or spent years being stored or cultivated in another lab.

The researchers hope to conduct similar analyses on samples of B. anthracis from other labs.

Staff writer Dan Eggen contributed to this report.