91av

THE attacker who sent anthrax spores through the US mail last autumn may not
have stolen the powder made by the US Army’s Dugway Proving Ground in Utah. If
so, the attacker must have known how to “weaponise” the bug.

That’s the implication of what 91av has learned about the
latest attempts to distinguish between the anthrax cultures held by different
labs. But astonishingly, it appears that federal investigators have not yet
collected all the samples that could tell them where the attacker got the
bacteria in the first place.

Distinguishing between different labs’ holdings, or accessions, of the Ames
strain used in the attacks is extremely difficult. There’s very little genetic
difference even between different strains of anthrax, so spotting differences
within a strain is harder still.

Paul Keim of Northern Arizona University at Flagstaff, who has been leading
the genetic analysis of the anthrax since the first victim was diagnosed, has
been focusing on regions in the bacterial genome where there are varying numbers
of repeats. This at first turned up no differences between the Ames lineages
(91av, 9 February p 8).
But Keim told a conference on
microbial genomes in Las Vegas last month that he has discovered a repeat region
that does vary. “We can distinguish among different Ames accessions,” Keim told
91av.

Keim is not allowed to say what labs are involved. But his collection
includes samples from the US Army Medical Research Institute for Infectious
Diseases in Fort Detrick, Maryland, and from Dugway. Keim’s team has been unable
to distinguish between the attacker’s bacteria and a sample that came from the
British biodefence laboratory at Porton Down, which in turn acquired the
bacteria from USAMRIID.

That suggests that differences have emerged between the attacker’s anthrax
and samples from Dugway—the only lab known to have recently produced the
kind of fine, floating spore powder used in the attack. So if Dugway’s bacteria
are genetically different from the attacker’s, it seems likely that he or she
acquired a culture, possibly from USAMRIID, and weaponised it. That narrows the
field to someone with access to fairly specialised equipment.

It will be impossible to home in on the source, however, until Keim’s team
has been able to compare samples from the over 20 labs known to have acquired
the Ames strain from USAMRIID. But so far, the team has analysed only bacteria
from the victims of the attack—which have all been identical—and
from the few labs that had provided samples for Keim’s collection before the
attacks.

“No one knows of anyone who has been subpoenaed by the FBI to provide copies
of cultures in their care,” says Martin Hugh-Jones of Louisiana State University
at Baton Rouge, who helped compile the collection of cultures used by Keim.
Various labs have received subpoenas for records of cultures and people who had
access to them. But the FBI has not demanded actual bacteria for analysis.