Taking anthrax's fingerprint


Search: The FBI is turning to genetic researchers to help narrow its investigation into last year's attacks, hoping they can identify where the deadly bacteria came from.

May 10, 2002|By Scott Shane | Scott Shane,SUN STAFF

Whoever mailed the anthrax that killed five people last fall took pains not to leave any fingerprints on the envelopes. What the perpetrator may not have realized is that the anthrax itself has a fingerprint.

With little evidence of progress in the FBI's 7-month-old investigation, investigators are hoping genetic sleuthing can narrow the search by determining where the anthrax came from.

In principle, at least, the fast-advancing science of genomics has made that possible. In an article published yesterday on the Science magazine Web site, scientists from the Institute for Genomic Research in Rockville and Northern Arizona University say they have identified tiny differences between the DNA of the Ames-strain anthrax used in the attacks and some, though not all, other specimens of Ames anthrax.

"The major point is that you can take two closely related strains, sequence the genomes and find differences," says Timothy D. Read, a geneticist at the Institute for Genomic Research and the lead author of the study.

Ultimately, the ability to identify minute differences between samples of bacteria and other pathogens may play a role not only in tracking bioterrorists, but in understanding disease epidemics and settling patent disputes over bioengineered microbes or plants, says the British-born Read, who began studying anthrax two years before the attacks put it on the front page.

Finding mutations in the more than 5 million base pairs, or "letters" of genetic code, in the DNA of the anthrax bacterium to tell one sample from another is like hunting for typos in a telephone book. Bacillus anthracis is what biologists call a "conservative" organism - one that changes very slowly. The errors that creep into any complex analysis threaten to mask real, but minuscule, differences.

In their study, the scientists looked at anthrax cultured from the body of Robert Stevens, the Florida photo editor who was the first person to die in the mail attacks. Then they compared their findings at 60 specific genetic markers - places where letters are most likely to be repeated or dropped - with seven other samples of anthrax.

The scientists managed to distinguish five of the samples from the anthrax that killed Stevens. They found that the mailed anthrax almost certainly came from a laboratory that got its initial supply from the Army's biodefense center at Fort Detrick, which distributed Ames to numerous labs over the past 20 years.

But it proved impossible to find differences between the Stevens sample and two other samples of Ames anthrax. So while the separate genetic analysis being conducted for the FBI may eliminate some labs as possible sources, it is unlikely to pinpoint the lab where the mailed anthrax originated.

"I think it's a neat piece of work," says Martin E. Hugh-Jones, a veterinary epidemiologist at Louisiana State University and one of the world's top authorities on anthrax. He said he was particularly interested to see that a sample of Ames collected from a dead goat in Texas in 1997 did not match the Stevens sample, suggesting that the anthrax attacker got his weapon from a lab, not from the wild.

The FBI's secret analysis by Northern Arizona geneticist Paul Keim is not complete, having been delayed for months while procedures were developed and a lab prepared at Fort Detrick to receive samples. The delay has been sharply criticized by some scientists.

"If the FBI thought it was really going to be useful, it could have been done long before now," says Barbara Hatch Rosenberg, a molecular biologist at the State University of New York who has followed the investigation closely. "But I don't think it will help solve the case. So I'm not holding my breath."

Whatever it may contribute to the sleuthing, genetic analysis has gone a long way toward sketching the family tree of anthrax. For example, it shows that Ames, the most common strain in U.S. labs, traces its ancestry to cattle herds in Turkey, wool mills in India and dusty fields in Australia.

Before genetic analysis became possible, the veterinarians and biological weapons makers who studied the bacteria had no reliable way of distinguishing one strain of anthrax from another.

There was no system for naming strains, just nicknames or numbers. "Buffalo" was cultured from a dead buffalo. The Sterne strain was named for the Italian veterinarian who used it to develop an animal vaccine. Vollum, used in the U.S. bioweapons program in the 1950s and 1960s, was named for a British pathologist.

Ames was labeled 20 years ago by Gregory B. Knudson, a scientist then at the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick. Ames - which Knudson then believed came from Ames, Iowa, but discovered recently was from a dead cow in Texas - proved especially lethal. It became the Army's favored strain for vaccine testing, and Fort Detrick researchers supplied it to scientists at many other labs.

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