Disease
C. botulinum causes botulism.
Transmission
Spores, widespread in soil, contaminate vegetables, and meats. When these foods are canned or vacuum-packed without adequate sterilization, spores survive and germinate in the anaerobic environment. Toxin is produced within the canned food and ingested preformed. The highest-risk foods are (1) alkaline vegetables such as green beans, peppers, and mush rooms and (2) smoked fish. The toxin is relatively heat-labile; it is inactivated by boiling for several minutes. Thus, disease can be prevented by sufficient cooking.
Pathogenesis
Botulinum toxin is absorbed from the gut and carried via the blood to peripheral nerve synapses, where it blocks the release of acetylcholine. It is a protease that cleaves the proteins involved in acetylcholine release. The toxin is a polypeptide encoded by a lysogenic phage. Along with tetanus toxin, it is among the most toxic substances known. There are eight immunologic types of toxin; types A, B, and E are the most common in human illness. Botox is a commercial preparation of exotoxin A used to remove wrinkles on the face. Minute amounts of the toxin are effective in the treatment of certain spasmodic muscle disorders such as torticollis, “writer’s cramp,” and blepharospasm.
Clinical Findings
Descending weakness and paralysis of cranial nerves, including diplopia, dysphagia, ptosis, and respiratory muscle failure, are seen. No fever is present. In contrast, Guillain-Barré syndrome is an ascending paralysis.
Two special clinical forms occur: (1) wound botulism, in which spores contaminate a wound, germinate, and produce toxin at the site and (2) infant botulism, in which the organisms grow in the gut and produce the toxin there. Ingestion of honey containing the organism is implicated in transmission of infant botulism. Affected infants develop weakness or paralysis and may need respiratory support but usually recover spontaneously. In the United States, infant botulism accounts for about half of the cases of botulism, and wound botulism is associated with drug abuse, especially skin-popping with black tar heroin.
Laboratory Diagnosis
The organism is usually not cultured. Botulinum toxin is demonstrable in uneaten food and the patient’s serum by mouse protection tests. Mice are inoculated with a sample of the clinical specimen and will die unless protected by antitoxin. Enzyme linked immunoassay (EIA) tests are also used to detect the toxin, and PCR tests are used to detect the DNA encoding the toxin.
Treatment
Treatment with antiserum should not be delayed while waiting for laboratory results. The heptavalent antitoxin containing all seven types (A–G) is preferred to the trivalent antitoxin containing types A, B, and E. Respiratory support is provided as well. The antitoxin is made in horses, and serum sickness may occur. A bivalent antitoxin (types A and B) purified from the plasma of humans immunized with
Prevention
Proper sterilization of all canned and vacuum-packed foods is essential. Food must be adequately cooked to inactivate the toxin. Swollen cans must be discarded (clostridial proteolytic enzymes form gas, which swells cans)
