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INVESTIGATORS in the US are analysing samples of anthrax stocks held by
research labs in a bid to identify the source of the bioterrorist attacks that
have killed five Americans.

The hunt is now focusing on labs in the US from which those responsible for
the attacks may have obtained the bacteria. Officials had said that too many
labs held samples of the Ames strain used in the attacks to narrow down the
source.

Now researchers say the particular variant of Ames used in the attacks was
held primarily by the US Army Medical Research Institute for Infectious Diseases
in Fort Detrick, Maryland, and distributed to a fairly limited number of
researchers. Anthrax researchers have recently developed highly sensitive
techniques that reveal tiny differences between the DNA of anthrax samples,
which are otherwise very hard to tell apart. Tests are now under way to see how
closely the genetic fingerprint of the anthrax used in the attacks matches those
of bacteria held at different labs around the US.

Meanwhile, proof has emerged that contaminated mail has spread spores to
unexpected destinations. It now seems likely that the latest victim, an elderly
woman in Connecticut, was infected by a letter that passed through contaminated
sorting equipment.

Spores have been found on another letter that was handled at the victim’s
local sorting office and sent to a nearby town. Its postmark reveals that this
letter passed through postal machines in Trenton, New Jersey, at nearly the same
time as anthrax-laced letters that were sent to two senators.

No one yet knows how many letters were contaminated as they passed through
the sorting machines. Although such letters may have spread anthrax far and
wide, the tiny doses they carry might only be revealed if elderly people or
those with a weakened immune system are exposed and become sick.