- WASHINGTON (Reuters) - A
mutated form of the toxin in the anthrax bacterium could be used to make
a fast-acting medicine for people exposed to biological weapons using the
deadly germ, as well as a new form of vaccine, scientists said on
Thursday.
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- Harvard Medical School researchers tested whether they
could prevent infection using a form of anthrax containing a mutation in
a toxin produced by the bacterium.
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- When the mutant form was injected together with
the normally
lethal mix of anthrax toxin, laboratory rats did not develop any symptoms
of poisoning, according to the study appearing in the journal
Science.
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- Rats infected with the toxin without the mutant variation
became moribund within 90 minutes.
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- ``What we've been able to do is to take a component of
a toxin and, by making a mutational change in it, you now convert that
piece of a toxin into something that will interfere with toxicity,'' lead
researcher R. John Collier said in an interview. ``It's a novel way to
interfere with a bacterial infectious process -- something
entirely new.''
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- Anthrax is a bacterial disease that generally infects
animals such as cattle, sheep and hippopotamuses. It rarely infects humans,
but could pose a devastating threat if anthrax spores are used in
a biological
weapon by terrorists or in warfare. Not surprisingly, the findings have
drawn the interest of the U.S. military.
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- Death is caused by the toxin produced by the bacteria.
In its airborne form, a mere teaspoonful of anthrax could wipe out hundreds
of people. A big worry is the possible release of anthrax by terrorists
in an urban setting.
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- The Harvard team sought to prevent infection using forms
of the anthrax bacterium with a mutation in a toxin component
called protective
antigen.
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- The anthrax bacterium secretes three toxin proteins into
the bloodstream: protective antigen, lethal factor and edema factor. These
assemble into the toxin on the outside surface of human cell membranes.
For symptoms to develop, lethal factor and edema factor must move to the
cell interior.
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- Normally, seven protective-antigen molecules
form a doughnut-shaped
channel that allows the two other proteins to cross the usually
impenetrable
cell membrane and enter the cytoplasm, where they disrupt cell function.
But Collier said the mutants appeared to block the formation of
this channel.
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- A Post-Infection Drug Foreseen
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- Mutant protective antigen may serve both as an anthrax
vaccine and as a fast-acting and broadly protective drug after infection,
Collier said. The researchers said future studies involving mice will be
conducted at U.S. Army laboratories in Maryland.
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- A vaccine currently exists, but very few outside the
military are immunized. The only current way to treat anthrax
after exposure
is with antibiotics before symptoms occur.
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- ``Once an individual becomes symptomatic, it's
too late,''
Collier said. ``The thing about the inhalational form is that the disease
very rapidly progresses from the lungs into the bloodstream, with
the result
being almost uniformly fatal in a few days.''
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- Collier said his prime worry is not the use of anthrax
in traditional warfare, but as a possible terrorist weapon. He
said a Japanese
cult once tried and failed to employ anthrax as a weapon, but
other extremists
may try again.
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- ``The great fear is that this could be used in
a terrorist
attack on a domestic population,'' Collier said. ``So I think that the
domestic authorities could quite possibly be interested, and should be
(in the possible future drug). ... This is something that you might want
to stockpile in major metropolitan areas around the country and
have available.''
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- Collier said that the approach his team used on anthrax
perhaps could be used against other disease-causing bacteria,
such as Staphylococcus,
that act similarly.
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