杏吧原创

SUSPICIONS that the perpetrator of last year鈥檚 anthrax attacks used bugs that came from the US Army were strengthened last week by the publication of their DNA sequence. But tests that could further narrow down the source have yet to begin.

When the attacks began last October, The Institute for Genomic Research in Rockville, Maryland, had already begun sequencing anthrax. By luck, TIGR had chosen a variant of the 鈥淎mes鈥� strain the attacker used. The institute joined forces with Paul Keim at Northern Arizona University at Flagstaff to sequence the attack variant as well.

They found many genetic differences between the two. So the teams then compared the attack strain with four disease-causing Ames samples in Keim鈥檚 collection, looking only at the variable regions. They found four differences between the attack bacteria and one of the samples, taken from a goat in Texas in 1997, proving that this approach can distinguish between very closely related lineages. But of the other three samples, only one was slightly different from the attack strain.

These three samples are identified in the paper only as B, C and D. But New 杏吧原创 can deduce, from previous statements by the scientists, that two of Keim鈥檚 samples are from the Army Medical Research Institute of Infectious Diseases at Fort Detrick, Maryland, and the other is from the US Army proving ground at Dugway, Utah. That means B and C, the samples identical to the attack strain, are probably from USAMRIID, and D, the slightly different strain, is likely to be from Dugway.

Dugway recently produced fine 鈥渨eaponised鈥� anthrax powder. But if its cultures differ from the attack strain, it seems unlikely that the attacker stole this powder. The suspicion that the attack powder was home-made is also supported by reports last week that it was finer in each successive letter, as though the attacker was improving the technique with each batch.

But even if the attack strain is identical to the USAMRIID samples, this still doesn鈥檛 prove the attacker got the bacteria directly from the US Army. Any one of a dozen or so labs given cultures of the USAMRIID strain could be the source. However, tests on these labs鈥� cultures could at least exclude some as the source by revealing differences.

Only in February, though, did the FBI finally demand samples for testing. The FBI said it first needed to devise a way of collecting the strains that would not legally compromise their use as evidence.

The samples are now at USAMRIID, but no one will say when or where they will be analysed, or why this has not yet begun. The whole process is legally unprecedented, and it seems likely that analysis of the samples is also awaiting a legally watertight procedure.