Subject: Is BT potentially dangerous?

From: Bob Batson <[email-masked]>
Date: Fri, 28 May 1999 14:46:29 -0500 (CDT)

>From the AGNET-L Mailing List:

RED FLAG FOR GREEN SPRAY
May 29, 1999
New Scientist
Debora Mackenzie
According to this story, French researchers have found that inhaling the
spores of Bacillus thuringiensis, or Bt, sprayed on organic crops as a
pesticide can cause lung inflammation, internal bleeding and death in
laboratory mice.

The story notes that dried Bt spores have been used as a pesticide for
more than 30 years and are one of the very few insecticides sanctioned
for use on organic crops in Europe. Bt is also widely used to combat
pest such as the spruce budworm, a caterpillar that attacks trees.

Last year, French scientists isolated a strain of Bt that destroyed
tissue in the wounds of a French soldier in Bosnia. The strain, known as
H34, also infected wounds in immunosuppressed mice (This Week, 30 May
1998, p 7). Now the same team has found that H34 can kill mice with
intact immune systems if they inhale the spores.

Francoise Ramisse of le Bouchet army research laboratories near Paris
and her colleagues were cited as finding that healthy mice inhaling 108
spores of Bt H34 died within eight hours from internal bleeding and
tissue damage. Spores from mutants of the same strain which did not
produce the insecticide were equally lethal to mice, suggesting that it
was not to blame. Ramisse and her colleagues presented their results at
a conference in Paris last month. The researchers think that the
symptoms are caused by other toxins. The bacterium's close cousin,
Bacillus cereus, produces a toxin that ruptures cell membranes. And in
1991, Japanese researchers showed that B. thuringiensis produces the
same toxin. In fact, when the French researchers ran samples from the
soldier from Bosnia through an automated medical analyser, it seemed to
show that the bacterium was B. cereus. Ramisse suggest that companies
producing Bt spores might make them safer by deleting the promoter
sequence that activates the gene for the membrane-rupturing toxin.

Although H34 is not used as a pesticide, commercial strains of Bt tested
by the researchers also killed some mice or caused lung inflammation
when inhaled. The team obtained these strains from Abbott Laboratories,
a major supplier of Bt based in Chicago. Ramisse points out that the
strains are sprayed on forest pests at concentrations of 1011 spores per
square metre--and so might pose a danger to people in the immediate
vicinity. But Abbott maintains that Bt is safe. Linda Gretton, a company
spokeswoman, was quoted as saying, "We stand by our products." The
French researchers have not yet tested strains made by other companies.

The story notes that recorded infections by Bacillus pathogens are
comparatively rare.  Known pathogenic species can have very distinctive
symptoms. Anthrax, for instance, is caused by B. anthracis. But where
such tell-tale signs are absent, Ramisse suspects that doctors often
fail to recognise that the bacteria are responsible, dismissing any
Bacillus in patients' cultures as contamination.  Consequently, the
cultures are often discarded.

When Bt was sprayed in towns in Oregon in 1991 to combat gypsy moths,
the bacterium was found in clinical samples from 55 patients who had
been admitted to hospital for a variety of other reasons. Robert Haward
of the Soil Association, which represents Britain's organic farmers, was
cited as saying that they may have to use masks and take more care when
spraying the spores on crops.

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Bob Batson                              L 39 12 14 N  94 33 16 W
[email-masked]                             Kansas City
TCS - Mystic Fire Priest                USDA zone 5b
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Under the most controlled conditions, the experimental apparatus will
do exactly as it pleases.