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Scientists Find New Clues to US Anthrax Attacks - 2002-05-09

U.S. government investigators trying to find who sent anthrax through the mail last year have new clues to go on. Scientists analyzing the strain that killed several people have discovered that it has distinctive genetic features that could possibly reveal its source. But, the evidence is very slim. Investigators have known since October that the bioterrorists who sent letters containing anthrax spores to U.S. journalists, politicians, and others used a strain called Ames. The Ames strain was originally collected from a dead cow in Texas back in 1981, sent to a U.S. Army laboratory in Maryland and later forwarded for experiments to 14 other labs.

Because microbes mutate slightly during reproduction, it is possible that the anthrax strain at each lab became genetically different from the rest. If one of them happens to match the attack strain, investigators may then have a lead in apprehending the bioterrorists.

Now an analysis of this strain, called the Florida strain, has revealed genetic markers that distinguish it from other strains. Microbiologist Timothy Read of The Institute for Genomic Research near Washington, D.C. says the markers he and his colleagues discovered might be useful in the anthrax probe.

"They might, for instance, be used to possibly exclude strains from some laboratories that obviously are not similar to the Florida strain in those markers," he said.

But Mr. Read's study in the journal Science points out something that may hinder the forensic probe: the differences in the mutations between the Florida Ames strain and six others his team looked at are extremely small.

"The strains are very, very closely related to each other," he said. "So, it is possible that these specific markers may not be informative. I hope they are, but it is possible they may not be."

But Barbara Hatch Rosenberg is more emphatic. She is following the progress of the anthrax investigation for the Federation of American Scientists and claims that the new research is practically useless for this purpose.

"It does not add anything that we did not already know to the present investigation," she said. "This is not going to be overwhelming data. It is too close to marginal. There may be some indication, but we cannot be certain of that even until they have looked."

To understand the role genetic markers play as a forensic tool, think of human fingerprints. Those found at a crime scene must be compared to a database of many sets of fingerprints, one of which may belong to the criminal. Having only a few fingerprint samples to work from is futile. Stanford University infectious disease physician David Relman says the same concept applies to the new markers for the attack strain of anthrax.

"Although this is an important first step, what now is missing is a fleshing out of the database," he said. "They need to survey and analyze a lot of strains for the presence or absence of these particular new markers and expand the collection of markers because the ones they have identified now will not be sufficient to resolve all of the differences between very closely related organisms."

U.S. health officials have given The Institute for Genomic Research money to do that with at least 14 more anthrax strains.

The researchers say genetic analysis is a powerful new tool for probing the origin of many different infectious disease outbreaks, whether they represent biological warfare attacks, natural emerging diseases, or more familiar ailments. Barbara Hatch Rosenberg, like many scientists and public health officials, advocates developing a global genetic database of such microbes.

"It can help to determine the origin of an outbreak and, in that sense, it can deter the use of a biological agent for a weapon if it could be readily attributed to some particular origin,"she said. "It also can immediately help in determining how serious the outbreak may be and what the treatment should be and the response in general."

Such a database would take years to build. For now, the U.S. Federal Bureau of Investigation is interested mainly in the anthrax genome and has been given the latest findings to follow up on.