- As anthrax continues to turn up in US postal facilities,
and postal workers, evidence is emerging that it is an American product.
Not only are the bacteria genetically close to the strain the US used in
its own anthrax weapons in the 1960s, but New Scientist can reveal that
the spores also seem to have been prepared according to the secret US
- This is troubling, say bioterrorism specialists. While
the terrorists behind the anthrax-laced mail US might have got hold of
the strain of anthrax in several laboratories around the world, the method
the US developed for turning a wet bacterial culture into a dangerous,
dry powder is a closely-guarded secret.
- Its apparent use in the current spate of attacks could
mean the secret is out. An alternative is that someone is using anthrax
produced by the old US biological weapons programme that ended in 1969
- in which case the scope for further attacks could be limited. Experiments
to determine which is true are underway now in the US.
- Particle Size
- Analysis of the physical form of the anthrax powder used
in the attacks has lagged behind the genetic analysis. Bacteria from
or contaminated surfaces can be multiplied up to provide enough DNA for
analysis. But a physical examination requires a sample of the actual
and so far, only two are known. One is from the letter opened in Senator
Tom Daschle's office in Washington on 15 October, the other from a letter
sent to the New York Post.
- Last week, US Senator Bill Frist announced that the
in the Daschle letter was in particles 1.5 to 3.0 microns wide, a very
narrow size range. The results of the physical analysis of the New York
Post letter are not yet known.
- The actual bacterial spore is ovoid and around half a
micron wide. The whole trick to making anthrax weapons, says Ken Alibek,
the former deputy head of the Soviet Union's bioweapons programme, is to
turn wet cultures of bacteria into dry clumps of spores that are each
one and five microns wide, the optimal size to penetrate a human lung and
- But dried spores tend to form larger particles, with
a static electric charge that makes them cling doggedly to surfaces rather
than floating through the air where they can be inhaled.
- Fluidising Agent
- The Soviet Union got around this by grinding dried
along with chemicals that cause the particles to remain separate. Iraq
is the only other state known to have tried making such a weapon, and it
dried anthrax cultures along with bentonite, a clay used as a fluidising
agent in powders. But last week the White House said there was no bentonite
in the Daschle letter.
- For its weapon, say informed sources, the US added
molecules, including surfactants, to the wet spores so that when they were
dried, they broke up into fine particles within a very narrow size range
of a few microns. There was no need to grind the powder further. Chemical
tests are now being conducted to see if any traces of the US additives
- Grinding was considered the most likely way for
to create anthrax powders, as the milling machinery is not hard to obtain.
But it results in a wider range of particle sizes. Large particles can
be filtered out, but smaller ones remain. The Daschle anthrax, say sources,
looks instead like it was made according to the US recipe.
- Anthrax Stockpile
- The question is, when? At its peak, the US bioweapons
programme made 900 kilograms of dry anthrax powder per year at a plant
in Arkansas. That stockpile was destroyed when the US renounced bioweapons
in 1969. But small samples might have been saved without being
- Experiments are now underway in the US to determine how
many bacterial generations separate the anthrax being used in the attacks
from the most closely related strains in a reference collection of anthrax,
which includes the US weapons strain.
- If the number is very small, and the anthrax closely
resembles the weapons strain genetically, it could be a leftover from
production before 1969.
- If, however, the bacteria have gone through many cell
divisions since the most closely related strain was frozen, they might
have been produced more recently. That would mean someone has obtained
not only a virulent strain of anthrax, but the know-how to turn it into
what was probably the most sophisticated anthrax weapon ever
Site Served by TheHostPros