Human botulism can occur primarily as food-borne botulism, infant botulism or wound botulism.
Food-borne botulism is caused by eating food contaminated with preformed botulinum neurotoxin. The causative organism is Clostridium botulinum, an anaerobic, rod-shaped bacterium that produces heat resistant spores. The spores are universally distributed, occurring in soils, freshwater and marine sediments and the intestinal tracts of many animals. For an outbreak of food-borne botulism to occur, the spores must contaminate food, grow and produce neurotoxin. After the contaminated food is consumed, the neurotoxin is absorbed from the digestive system. The characteristic symptoms usually develop in 12 to 36 hours after consumption of the food. In extreme cases symptoms may occur as soon as 2 hours or as long as 14 days after consumption of the food. Symptoms include nausea, vomiting, diarrhea, weakness, dizziness and vertigo, ptosis (drooping of the eyelids), dysphagia (difficulty in swallowing), blurred vision, diplopia, constipation, dry mouth and others. The neurotoxin affects nerve terminals of the parasympathetic nervous system. Specifically, the neurotoxin inhibits release of the neurotransmitter acetylcholine at the neuromuscular junction. Death may result from asphyxiation caused by paralysis of the diaphragm. The fatality rate has declined from over 60% to less than 10% because antitoxin is administered promptly in suspected cases and because mechanical respirators are used. See Food Poisoning.
Control of Food-borne Botulism
Control of food-borne botulism is based almost entirely on thermal destruction of the spores or inhibition of spore germination and bacterial cell growth in foods. Through the establishment and enforcement of strict, standardized time-temperature treatments of canned foods, the commercial food-canning industry has been successful in preventing botulism. Home canning may lead to botulism because the time-temperature treatment of foods may be insufficient to kill spores, especially in "low-acid" foods (eg, corn, peppers, green beans, asparagus, mushrooms, eggplant). Home canners should use approved pressure-cooker processes for such products and follow instructions carefully, including adding sufficient amounts of salt and/or vinegar. Foods other than canned foods have been implicated in botulism outbreaks. Foods with instructions for refrigeration must be kept refrigerated to reduce the risk of botulism poisoning. Some traditional foods of the native peoples of Canada, including whale, seal and walrus meat and salmon eggs, present special problems. Preservation of these foods in various fermented or dried forms may be conducive to the growth of C. botulinum.
Wound botulism results from infection of a wound with spores of Clostridium botulinum which grow and produce neurotoxin in the wound. While wound botulism is rare, it is being increasingly associated with intravenous drug use.
Infant botulism is caused by ingestion of viable spores that germinate, colonize and produce neurotoxin in the intestinal tract of infants under one year of age. Infant botulism was first recognized in 1976 and is now the most common form of botulism in the United States. Honey should never be used on a soother to quiet a fussy or colicky baby, or otherwise fed to infants under one year of age. Spores of C. botulinum which are found in air and soil, can contaminate honey and may persist even in pasteurized honey. In healthy children and adults, these spores do not cause illness, but infants are particularly susceptible. Ingested spores can germinate and produce neurotoxin because the infant digestive system is not yet resistant to C. botulinum. An additional category, unclassified, includes cases of unknown origin and adult cases which resemble infant botulism. Animal botulism affects cattle and birds worldwide and occurs to a lesser extent in various other animals.