What is botulism?

Causes and Symptoms

Clostridium botulinum is a bacillus that produces spores. Both bacteria and spores can be found in the intestines of humans and other animals as well as in contaminated soil and water. The spores are highly resistant to heat and can survive boiling and other measures employed to kill bacteria and destroy toxins for safe food preparation. Under appropriate anaerobic conditions (those lacking oxygen), the spores germinate into the toxin-producing vegetative bacilli. The exotoxin is a protein synthesized within the bacteria and released only after the death and lysis (disintegration) of the bacteria. When ingested, the toxin resists the acid and enzymes of the stomach by creating complexes with other bacterial proteins. This allows the toxin to reach the intestines, where it is absorbed into the bloodstream and carried to nerve endings. The toxin is bound and internalized into the presynaptic nerve
endings, preventing release of the neurotransmitter acetylcholine. The binding is irreversible, and recovery can occur only after nerve endings regenerate.

Human illness is caused by toxin ingestion or the entry of toxin-producing bacteria into the host. Improper processing of food, especially home canning, can result in the germination of contaminating spores, with subsequent toxin production. Food poisoning
occurs when toxin-containing food is ingested, unless it has has been heated sufficiently to denature the protein toxin.

The symptoms of descending paralysis usually begin twelve to thirty-six hours after ingestion. Blurred vision, slurred speech, and difficulty swallowing are followed by labored breathing and weakness of the upper and then the lower extremities. Spores may also contaminate a wound and then germinate and form toxin within the host, producing symptoms similar to food poisoning. Botulism is diagnosed by identification of the toxin and/or bacteria in the patient’s serum, stool, or wound, or in ingested food. The specific type of botulinum toxin is verified using the mouse neutralization test.

Treatment and Therapy

The outcome of botulism has improved with the development of critical care and supportive measures. Intubation and mechanical ventilation is vitally important until neuromuscular control of breathing is regained. Specific treatment with botulism antitoxin may be used in severe or progressive cases. Because this antitoxin is of equine origin, however, a high incidence of hypersensitivity reactions (9 to 20 percent) occurs in human patients.

Perspective and Prospects

In 1820, a German named Justinus Kerner first noted the association between sausage consumption and paralytic disease. The term botulism is derived from botulus, the Latin word for “sausage.” Wound botulism was first recognized in 1943. Infant botulism, which is caused by swallowed spores rather than preformed toxin, was first noted in 1976. The most common form of human botulism in the United States, infant botulism can be contracted from exposure to honey, but most cases seem to be related to spores found in soil and dust.

Despite these insights, however, the epidemiology of many botulism cases remains obscure. A diagnostic test more rapid and widely available than the mouse neutralization test, which takes forty-eight hours, is needed. Antitoxin, perhaps from deoxyribonucleic acid (DNA) hybridization technology, would improve therapy over the scarce and dangerous equine product.

Bibliography:

Brachman, Philip S., and Elias Abrutyn, eds. Bacterial Infections of Humans: Epidemiology and Control. 4th ed. New York: Springer, 2009.

Mandell, Gerald L., John E. Bennett, and Raphael Dolin, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. New York: Churchill, 2010.

MedlinePlus. "Botulism." MedlinePlus, Apr. 23, 2013.

Pommerville, Jeffery C. Alcamo’s Fundamentals of Microbiology. 9th ed. Sudbury, Mass.: Jones, 2010.

Wood, Debra. "Botulism." Health Library, Nov. 11, 2012.