GENTECH archive


more on Bt sprays

I can only add to the following that Bt crops don't make or have Bt spores.
Notice also that the insecticidal toxins are not to blame.

  Bt Sprays May Be Health Hazard

  Spores of Bacillus thuringiensis (Bt) sprayed on organic crops as a
pesticide may damage the health of people who inadvertently inhale
them. French researchers have found that inhaling the spores from
certain strains of can cause lung inflammation, internal bleeding and
even death in laboratory mice, according to a report in New Scientist.

  Dried Bt spores of the bacteria 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. It 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, was found to infect wounds in immunosuppressed
mice. Now the same team has found that H34 can kill mice with intact
immune systems if they breath the spores in. Françoise Ramisse of le
Bouchet army research laboratories near Paris and her colleagues
found 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
in April. The researchers think that the symptoms are caused by other
toxins. A related bacterium, Bacillus cereus, produces a toxin that
ruptures cell membranes, and in 1991, Japanese researchers showed
that B. thuringiensis produces the same toxin. 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, USA. 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. "We stand by our products,"
says Linda Gretton, a company spokeswoman. The French researchers
have not yet tested strains made by other companies. "I suspect Bt
infection is more widespread than we realise," says Ramisse, in the
magazine. 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. "I wish they would start keeping them
so we could check for Bt," she said to New Scientist. 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,
says that they may have to use masks and take more care when spraying
the spores on crops.

  May 1999