German physicians first identified botulism in the late 18th century when patients developed an often fatal disease after eating spoiled sausage. Five distinct clinical syndromes are now recognized: food-borne botulism, infant botulism, wound botulism, adult intestinal colonization, and iatrogenic botulism. Food-borne botulism, the best-known form, results from ingestion of preformed toxin in improperly preserved home-canned vegetables, fish, or meats. In the last few decades, noncanned foods have also been reported to cause food-borne botulism. Examples include fresh garlic in olive oil, sautéed onions, beef or turkey pot pie, baked potatoes, potato salad, smoked whitefish, turkey loaf, and turkey stuffing.
Mechanism of toxicity
Botulism is caused by a heat-labile neurotoxin (botulin) produced by the bacterium Clostridium botulinum. Different strains of the bacterium produce seven distinct exotoxins: A, B, C, D, E, F, and G; types A, B, and E are most frequently involved in human disease. Botulin toxin irreversibly binds to cholinergic nerve terminals and prevents acetylcholine release from the axon. Severe muscle weakness results, and death is caused by respiratory failure. Symptoms may be slow in onset but are sometimes rapidly progressive. The toxin does not cross the blood-brain barrier.
Botulinum spores are ubiquitous in nature, and except in infants (and in rare situations adults), the ingestion of spores is harmless. However, in an anaerobic environment with a pH of 4.6–7, the spores germinate and produce botulinum toxin. The spores are relatively heat-stable but can be destroyed by pressure cooking at a temperature of at least 120°C (250°F) for 30 minutes. The toxin is heat-labile and can be destroyed by boiling at 100°C (212°F) for 10 minutes or heating at 80°C (176°F) for 20 minutes. Nitrites added to meats and canned foods inhibit the growth of clostridia.
Toxic dose. Botulin toxin is extremely potent; as little as one taste of botulinum-contaminated food (approximately 0.05 mcg of toxin) may be fatal.
Classic food-borne botulism occurs after ingestion of preformed toxin in contaminated food. Initial symptoms are nonspecific and may include nausea, vomiting, sore throat, and abdominal discomfort. The onset of neurologic symptoms is typically delayed 12–36 hours but may vary from a few hours to as long as 8 days. The earlier the onset of symptoms, the more severe the illness. Diplopia, ptosis, sluggishly reactive pupils, dysarthria, dysphagia, dysphonia, and other cranial nerve weaknesses occur, followed by progressive symmetric descending paralysis. The patient's mentation remains clear, and there is no sensory loss. Pupils may be either dilated and unreactive or normal. Constipation and ileus resulting from decreased motility may occur. Profound weakness involving the respiratory muscles may cause respiratory failure and death.
Infant botulism, the most commonly reported type, is caused by ingestion of botulism spores (not preformed toxin) followed by in vivo production of toxin (typically type A or B) in the immature infant gut. Risk factors include age younger than 1 year, breastfeeding, and ingestion of corn syrup or honey (which commonly contains botulism spores). It has also occurred in ...