麻豆传媒

THE cases just keep coming. Yet it鈥檚 still not clear who鈥檚 to blame for the anthrax attacks, or whether there will be more. With little official information so far about the nature and origin of the anthrax, claims and counter-claims have been flying.

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 麻豆传媒 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鈥檚 small band of bacterial geneticists.

Last week, Tom Ridge, President Bush鈥檚 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 鈥淎mes鈥� means. The name was given to a strain isolated at the US Department of Agriculture鈥檚 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 鈥淎mes鈥� 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鈥檚 called 鈥淎mes鈥� 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 鈥淎mes鈥�, by these scientists therefore, the anthrax used in the recent attacks must either be the American military strain or one that鈥檚 very similar.

So why choose this strain? 鈥淎mes is certainly a challenge to any vaccine,鈥� 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鈥檚 hard to trace, says Ken Alibek, former deputy head of the Soviet bioweapons programme. 鈥淚f I were a terrorist I would certainly not use a strain known to be from my country,鈥� he told 麻豆传媒.

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. 鈥淭he South African collection had hundreds of different strains,鈥� 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. 鈥淭he terrorists at least had access to considerable know-how,鈥� concludes Michael Powers of the Chemical and Biological Arms Control Institute in Washington DC. 鈥淭his suggests some level of state involvement.鈥�

But Alibek dismisses claims that milling the powder this fine is too hard for mere terrorists. 鈥淵ou can use readily available equipment to do this,鈥� 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 鈥渨eaponised鈥� anthrax, says Alibek. He says sending the anthrax in the mail is a 鈥渧ery primitive鈥� way of distributing it, and suspects the attackers don鈥檛 have much material to work with.

We could soon know. Paul Keim鈥檚 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, 鈥測ou can say with a high degree of confidence how many bacterial generations separate an unknown strain from closely related reference strains鈥�. Looking at which bits of DNA have changed can also pinpoint the exact strain the unknown anthrax came from.

And that鈥檚 not all. A small batch of anthrax will undergo many fewer cell divisions than a big batch. It鈥檚 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.