By Will Dunham
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.
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.
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.
Rats infected
with the toxin without the mutant variation became moribund within
90 minutes.
``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.''
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.
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.
The Harvard
team sought to prevent infection using forms of the anthrax bacterium
with a mutation in a toxin component called protective antigen.
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.
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.
A Post-Infection
Drug Foreseen
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.
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.
``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.''
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.
``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.''
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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