Prominent voices in the US charge that the anthrax is so sophisticated it can only have been produced with the backing of a government. Their suspicions are directed at Iraq, which is known to have made anthrax and other bioweapons.
But New Scientist can reveal that the bacteria used in the attacks is not a strain that Iraq, or the former Soviet Union, mass-produced for weapons. In fact, it is either the same strain the US itself used to make anthrax weapons in the 1960s, or close to it. Neither the strain nor the physical form in which it has been sent out is particularly sophisticated, say bioweapons specialists.
What may matter more than the strain is how big a batch this anthrax came from. This could reveal not only how many more of these mailings we can expect, but also whether the bacteria were brewed in small-scale, makeshift labs or bigger facilities.
Work that could tell us is under way at a lab in the US. Crucial geopolitical decisions could rest on what emerges from the electrophoresis gels and computer programs of the lab's small band of bacterial geneticists.
Last week, Tom Ridge, President Bush's newly appointed Homeland Security adviser, stated that the anthrax sent to Florida, NBC and Senator Tom Daschle were all the same strain. An FBI spokesman in Florida confirmed the widespread reports that this was the Ames strain.
But there has been confusion over what "Ames" means. The name was given to a strain isolated at the US Department of Agriculture's veterinary lab in Ames, Iowa, in the 1930s. This strain, which was later shared with microbiologists around the world, still strikes cattle in the western US. Recent American military research publications also mention an "Ames" strain isolated from a cow in Iowa in 1980.
However, the scientists analysing the anthrax from the attacks are comparing its DNA with a library of strains collected from all over the world.
And in this collection, what's called "Ames" has more interesting origins. It emerged in the mid-1980s from a freezer at the Centre for Applied Microbiology and Research, the British biodefence establishment at Porton Down, Wiltshire.
Porton Down had acquired it from the US Army Medical Research Institute for Infectious Diseases in Maryland. It is, say those who compiled the library, the strain the US used when it produced anthrax weapons. That programme ended in 1969, and the mass-produced anthrax was destroyed, although the US and its allies kept samples. To be identified as "Ames", by these scientists therefore, the anthrax used in the recent attacks must either be the American military strain or one that's very similar.
So why choose this strain? "Ames is certainly a challenge to any vaccine," says Martin Hugh-Jones of Louisiana State University at Baton Rouge. When lab animals immunised with the vaccine now being given to thousands of American troops are exposed to anthrax, many are still killed by the Ames strain.
Alternatively, the attackers may simply have wanted a strain of proven virulence that's hard to trace, says Ken Alibek, former deputy head of the Soviet bioweapons programme. "If I were a terrorist I would certainly not use a strain known to be from my country," he told New Scientist.
The Soviets did not mass-produce Ames, says Alibek. Nor did the Iraqis. Like Britain in the 1940s, Iraq favoured the Vollum strain, isolated at Oxford in 1930, which has been identified in samples from its Al Hakam plant. And the White House reiterated last week that all anthrax mass-produced in the US was destroyed after 1969.
Despite this, Ames would not have been have been hard to find. Samples of the weapons strain were kept in the US and elsewhere. "The South African collection had hundreds of different strains," Alibek points out. And Wouter Basson, former head of the South African bioweapons programme, made several trips to Libya after the fall of the apartheid government in 1994. Ames could also, of course, have been obtained by someone in the US.
Important clues also come from the size of the particles used in the attacks. According to reports last week, they had been milled down to a few micrometres, which is optimal for causing the inhalation form of the disease.
"The terrorists at least had access to considerable know-how," concludes Michael Powers of the Chemical and Biological Arms Control Institute in Washington DC. "This suggests some level of state involvement."
But Alibek dismisses claims that milling the powder this fine is too hard for mere terrorists. "You can use readily available equipment to do this," he says. His view is supported by a secret experiment last year called Project Bacchus, in which employees of the US Department of Defense covertly produced a kilogram of bacteria similar to anthrax. It was milled to a few micrometres using machines available openly in the US.
Nevertheless, the attacks have caused relatively few inhalation cases so far, which suggests that the spores were not blended with the anti-caking chemicals used in anthrax weapons to promote airborne spread. This is the secret of "weaponised" anthrax, says Alibek. He says sending the anthrax in the mail is a "very primitive" way of distributing it, and suspects the attackers don't have much material to work with.
We could soon know. Paul Keim's team at Northern Arizona University in Flagstaff has pioneered the genetic analysis of anthrax bacilli. Recently, says team member Kimothy Smith, they have found that some DNA regions mutate frequently, as often as once in every 1000 cell divisions.
By comparing the amount of mutation, says Smith, "you can say with a high degree of confidence how many bacterial generations separate an unknown strain from closely related reference strains". Looking at which bits of DNA have changed can also pinpoint the exact strain the unknown anthrax came from.
And that's not all. A small batch of anthrax will undergo many fewer cell divisions than a big batch. It's possible that the analysis could reveal whether the anthrax came from a 50-litre fermenter of the kind Project Bacchus obtained or the huge vats of a state-sponsored bioweapons facility. That could reveal how big an operation the attackers had--and whether we must expect yet more attacks.
Author: Debora MacKenzie
New Scientist issue: 27 October 2001
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