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BACKGROUND

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Infant botulism, the most common form of botulism encountered in the United States, has a unique pathogenesis. Unlike food-borne botulism, which results from the ingestion of preformed toxin, infant botulism occurs following the ingestion of Clostridium botulinum spores that germinate and colonize the infant gut. Botulinum neurotoxin is produced in vivo and absorbed, producing clinical disease. This form of botulism occurs almost exclusively in children younger than 1 year1. The first clear association of in vivo production of botulinum neurotoxin and a syndrome of weakness in infants was described in 1976.2 Subsequently, the pathophysiology, epidemiology, clinical manifestations, and specific therapy have been elucidated.

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PATHOPHYSIOLOGY

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C. botulinum is a gram-positive, spore-forming, obligate anaerobe that is found worldwide in soil and dust. Approximately 90% of U.S. cases of infant botulism are caused by toxin types A and B. However, cases due to toxin type E from C. butyricum and toxin type F from C. baratii have been reported.3 The spores can be found on fresh fruits and vegetables and in honey. The infant intestinal microflora plays a critical role in the pathophysiology of infant botulism. Experiments in mice show that adult mouse microflora completely inhibits gut colonization with C. botulinum or that significantly higher numbers of spores are required for successful colonization than in infant mice.4 Honey is the only food that has been unequivocally linked to specific cases of infant botulism.5 Corn syrup was implicated as a source of infection in the past, but changes in the production process have largely eliminated the risk of infection from corn syrup.6 With the decrease in the ingestion of honey by infants, the exact source of the spores is rarely found in individual cases.3 Once the spores are ingested botulinum toxin is produced in the gut. Then it is absorbed into the bloodstream and carried to peripheral cholinergic synapses, where it blocks the release of acetylcholine. Autonomic effects occur, as well as the classic somatic muscle weakness or paralysis. Botulinum toxin does not penetrate the central nervous system.1

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EPIDEMIOLOGY

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Although C. botulinum spores are ubiquitous, there is a clear geographic clustering of cases. The majority of reported cases are from California and the eastern Pennsylvania, New Jersey, and Delaware region, apparently mirroring the geographic distribution of spores. Toxin serotype also varies geographically. Type B toxin causes about 90% of cases in Pennsylvania, whereas the majority of California cases are due to type A toxin.5 All reported cases of infant botulism have occurred in patients under one year of age, and 95% of cases occurred in the first 6 months of life. C. baratii toxin-type F causes disease in younger infants.3 The youngest reported case was 38 hours old.7 No sex, race, or seasonal risk factors have been identified. Arnon and colleagues showed that the age distribution of infant botulism is almost ...

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