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Toxin produced by the bacterium Clostridium
botulinum is the main culprit in botulism. Other members of the
clostridium genus can produce botulinum toxin, namely C.
argentinense, C. butyricum, and C. baratii, but
they are minor sources. To grow, these bacteria require a low-acid,
oxygen-free environment that is warm (40-120°F or 4.4-48.8xC) and
moist. Lacking these conditions, the bacteria transform themselves
into spores that, like plant seeds, can remain dormant for years.
Clostridia and their spores exist all over the world, especially in
soil and aquatic sediments. They do not threaten human or animal
health until the spores encounter an environment that favors growth.
The spores then germinate, and the growing bacteria produce the
deadly botulism toxin.
Scientists have discovered that clostridia can
produce at least seven types of botulism toxin, identified as A, B,
C, D, E, F, and G. Humans are usually affected by A, B, E, and very
rarely F. Domesticated animals such as dogs, cattle, and mink are
affected by botulism C toxin, which also affects birds and has
caused massive die-offs in domestic bird flocks and wild waterfowl.
Botulism D toxin can cause illness in cattle, and horses succumb to
botulism A, B, and C toxin. There have been no confirmed human or
animal botulism cases linked to the G toxin.
In humans, botulinum toxin latches onto specific
proteins in nerve endings and irreversibly destroys them. These
proteins control the release of acetylcholine, a neurotransmitter
that stimulates muscle cells. With acetylcholine release blocked,
nerves are not able to stimulate muscles. Ironically, botulinum
toxin has found a beneficial niche in the world of medicine due to
this action. Certain medical disorders are characterized by
involuntary and uncontrollable muscle contractions. Medical
researchers have discovered that injecting a strictly controlled
dose of botulinum toxin into affected muscles inhibits excessive
muscle contractions. The muscle is partially paralyzed and normal
movement is retained.
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