Basic Information |
Botulism is an infection caused by the gram-positive, rod-shaped, anaerobic, spore-forming bacteria Clostridium botulinum. Clostridium botulinum is found in spore form in soils and on fruits, vegetables and seafood. Traditionally, homemade canned foods were of high concern for botulism. Improperly canned foods are the most common cause of botulism annually. More recently, though, the bacteria has been also been found in unrefrigerated homemade salsa, potatoes baked in aluminum foil, and salted or fermented fish. In infants, honey is the most common cause of botulism.
While C. botulinum spores are mostly harmless, under low oxygen conditions they can grow into active bacteria, which produces a severe neurotoxin. Seven different types of neurotoxin can be produced by C. botulinum, which are designated by letters A-G. Only types A, B, E, and F are known to cause illness in humans. Types C and D can cause illness in animals. There is an average of 145 botulism cases annually in the U.S., about 65% of which are infant botulism. Botulism can also originate in wounds--this type makes up about 20% of annual cases. Most of these injury related cases are associated with intravenous injection of black tar heroin. |
Mechanism Botulinum neurotoxin (BoNT) is one of the most toxic inhibitors of neurotransmitter release. It is a zinc-dependent protease that inhibits acetylcholine (Ach) release into the neuromuscular junction. BoNT acts preferentially on peripheral cholinergic nerve endings. When ingested or inhaled, BoNT can bind to epithelial cells and then be released into general circulation. BoNT is too large to pass through epithelial barriers by diffusion, so it is actively transported through gut lining. The use of general circulation is imperative for the lethal manifestations of botulism poisoning.
BoNTs are secreted as single polypeptide chains, but get cleaved to form a heavy chain and a light chain. The heavy chain is important in cell surface binding, while the light chain produces the toxic effect once inside the cell. |
Adverse Effects and Symptoms
There are 4 types of botulism infection: infant, foodborne, intestinal, and wound-related.
Infant botulism This is related to the ingestion of foods like honey during the first year of life. Symptoms usually appear between 18 and 36 hours of ingestion and include the following:
Foodborne botulism This occurs when food infected with BoNT is consumed. Symptoms related to foodborne botulism usually appear between 12 and 36 hours, but it can sometimes take several days at small doses. These symptoms include:
Intestinal botulism This occurs when C. botulinum spores are consumed and reproduce in the gastrointestinal tract to form live toxin producing bacteria. This form of botulism is extremely rare, but the symptoms are the same as those for foodborne botulism. Wound-related botulism This occurs with the germination of botulinum spores in an abscess. The timing of these symptoms is hard to measure, because the most known cases involve drug users who inject multiple times a day. Symptoms include:
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Treatment
Foodborne and intestinal botulism can be treated with an antitoxin, which binds to the BoNT in the bloodstream and blocks it from causing further damage to the nerves. This antitoxin, however, requires an early diagnosis because the antitoxin cannot reverse damage that has already occurred. Infant botulism is also treated with an antitoxin, though it is a slightly different antitoxin called "botulism immune globin." Wound botulism can be treated with antibiotics.
If botulism poisoning isn't diagnosed early enough, and breathing problems and paralysis occur, ventilators may be used along with intensive medical care. Rehab may also be used to rebuild muscle and help with nerve damage. |