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Botulism

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Lead author: Leah Tait

Overview


Botulism is the illness associated with Clostridium botulinum. There are three main types of the illness:

  • Food-borne botulism
  • Infant botulism
  • Wound botulism

Regardless of type, it is the production of botulinum toxin by Clostridium botulinum that is responsible for the illness. This paralytic illness is rare but potentially fatal.

The most common form of botulism is infant botulism. The CDC reports that 72% of all cases of botulism in the U.S. are infant botulism. It is most likely to occur in the first few months of infancy. Spores of the Clostridium botulinum bacteria colonize the gastrointestinal tract and once established, begin producing the botulinum toxin.

Food-borne botulism is the next most common, accounting for 25% of cases annually. Once primarily associated with improperly canned foods, food-borne botulism has more recently been associated with freshly prepared foods that have not been refrigerated correctly.

Wound botulism is the most rare form. It occurs when clostridial spores enter a wound, either through contaminated soil or through infected IV needles. The increasing popularity of "skin popping" black tar heroin has led to an increase in the cases of wound botulism, particularly in California, where the practice is the most widespread.

Symptoms


Symptoms of botulism may occur from as early as 6 hours after infection or as late as 14 days after. The toxin must first be absorbed into the bloodstream and the lymphatic system, after which it is distributed through the circulatory system to neuromuscular junctions. The botulinum toxin then acts by blocking the neurotransmitter acetylcholine, which prevents neurotransmission and causes flaccid paralysis.

Individuals with a mild case of botulism may experience:

  • Muscular weakness
  • Abdominal pain
  • Nausea and vomiting
  • Diarrhea

Individuals with more severe cases of botulism may experience:

  • Peripheral muscular weakness
  • Respiratory paralysis

The respiratory paralysis found in more severe cases can lead to death.

Diagnosis


The preliminary diagnosis is made considering the patient's history and physical symptoms. However, additional testing is necessary to confirm the diagnosis, as other diseases affecting the central nervous system may present similar symptoms. These include Guillain-Barré syndrome, stroke, and myasthenia gravis.

To definitively diagnose botulism, the botulinum toxin must be identified in the patient's serum, stool, or gastric aspirate. The standard laboratory test is the mouse bioassay, in which the patient's serum or sample is injected into mice and the mice examined for signs of botulism. However, this test takes up to 4 days to complete. As such, cases diagnosed only on clinical suspicions must be reported to public health authorities.


Treatment


If botulism is diagnosed early, equine antitoxin can be administered. This therapy is not useful in diagnoses at later stages as the antitoxin does not reverse the existing paralysis. (It cannot cross the nerve membrane to neutralize the botulinum toxin inside cells.) Supportive care, such as the use of a ventilator, may be necessary. The paralysis will slowly improve over the course of several weeks. Antibiotics are not used because killing the Clostridium botulinum bacteria may actually increase the rate at which botulinum toxin is released into the body.

Because the efficacy of treatment is so strongly connected to early diagnoses, it is essential that more rapid ways of diagnosing botulism be explored.


Prevention


Food-borne botulism can be prevented by maintaining sterile hygienic procedures when home-canning foods and by thoroughly cooking foods, as heat denatures the botulinum toxin.

Wound botulism can be prevented by getting medical care as soon as possible for infected wounds and by avoiding illicit use of IV drugs.

The incidence of infant botulism can be reduced by eliminating honey from the diets of infants less than a year old, as honey can contain spores of Clostridium botulism.


References


Bhidayasiri R,Choi YM, R Nishimura. 2004. Wound Botulism. Postgrad Med J. 80:240

Kent C. 1998. Basics of Toxicology. New York, NY:John Wiley & Sons, Inc.

Merrison AFA, Chidley KE, Dunnett J, Sieradzan KA. 2002. Wound botulism associated with subcutaneous drug use. BMJ. 325:1020-1021

S Cai, BR Singh, S Sharma. 2007. Botulism Diagnostics: From Clinical Symptoms to in vitro Assays. Critical Reviews in Microbiology, 33(2):109-125

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