Cause
C. botulinum is an anaerobic, Gram positive, spore-forming rod. Botulinium toxin is one of the most powerful known toxins: about one microgram is lethal to humans. It acts by blocking nerve function (neuromuscular blockade) through inhibition of the excitatory neurotransmitter acetyl choline's release from the presynaptic membrane of neuromuscular junctions in the somatic nervous system. This causes paralysis. Advanced botulism can cause respiratory failure by paralysing the muscles of the chest; this can progress to respiratory arrest.
In all cases illness is caused by the botulinium toxin produced by the bacterium C. botulinum in anaerobic conditions, and not by the bacterium itself. The pattern of damage occurs because the toxin affects nerves that fire (depolarise) at a higher frequency first.
Four main modes of entry for the toxin are known. The most common form in Western countries is infant botulism. This occurs in small children who are colonized with the bacterium during the early stages of their lives. The bacterium then releases the toxin into the intestine, which is absorbed into the bloodstream. The consumption of honey during the first year of life has been identified as a risk factor for infant botulism; it is a factor in a fifth of all cases. The adult form of infant botulism is termed adult intestinal toxemia, and is exceedingly rare.
Foodborne botulism results from contaminated foodstuffs in which C. botulinum spores have been allowed to germinate in anaerobic conditions. This typically occurs in home-canned food substances and fermented uncooked dishes. Given that multiple people often consume food from the same source, it is common for more than a single person to be affected simultaneously. Symptoms usually appear 12–36 hours after eating, but can also appear within 6 hours to 10 days.
Wound botulism results from the contamination of a wound with the bacteria, which then secrete the toxin into the bloodstream. This has become more common in intravenous drug users since the 1990s, especially people using black tar heroin and those injecting heroin into the skin rather than the veins.
Isolated cases of botulism have been described after inhalation by laboratory workers and after cosmetic use of inappropriate strengths of Botox.
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