Botulism is an uncommon, life-threatening poisoning caused by toxins produced by the bacteria Clostridium botulinum.
The toxins that cause botulism, which are the most potent poisons known, can severely impair nerve function. Botulism toxins paralyze muscles by preventing nerves from releasing a chemical messenger (neurotransmitter) called acetylcholine. Acetylcholine interacts with receptors on muscles (at the neuromuscular junction—see Overview of Neuromuscular Junction Disorders) and stimulates muscles to contract.
In very small doses, one of the botulism toxins can be used to relieve muscle spasms (because it reduces muscle activity) and to reduce wrinkles.
Clostridium botulinum bacteria form reproductive cells called spores. Like seeds, spores can exist in a dormant state for many years, and they are highly resistant to destruction. When moisture and nutrients are present and oxygen is absent (as in the intestine or sealed jars or cans), the spores start to grow and produce toxins. Some toxins produced by Clostridium botulinum are not destroyed by the intestine's protective enzymes.
Clostridium botulinum is common in the environment, and spores can be transported by air. Many cases of botulism result from ingesting or inhaling small amounts of soil or dust. Spores can also enter the body through the eyes or a break in the skin. However, most cases result from eating food that contains the toxins.
There are different forms of botulism, which have different causes.
Food-borne botulism occurs when food contaminated with the toxins is eaten. The most common sources of food-borne botulism are home-canned foods, particularly foods with a low acid content, such as asparagus, green beans, beets, and corn. Other sources include chopped garlic in oil, chili peppers, tomatoes, foil-wrapped baked potatoes that have been left at room temperature too long, and home-canned or fermented fish. However, about 10% of outbreaks result from eating commercially prepared foods—most commonly, vegetables, fish, fruits, and condiments (such as salsa). Less commonly, botulism results from eating beef, milk products, pork, poultry, and other foods.
Wound botulism occurs when Clostridium botulinum contaminates a wound or is introduced into other tissues. Inside the wound, the bacteria produce toxins that are absorbed into the bloodstream. Injecting drugs with needles that are not sterilized can cause this type of botulism, as can injecting contaminated heroin into a muscle or under the skin (skin popping).
Infant botulism develops in infants who eat food containing spores of the bacteria rather than toxins. The spores then grow in the infant's intestine, where they produce toxins. The cause of most cases is unknown, but some cases have been linked to the ingestion of honey. Infant botulism occurs most commonly among infants younger than 6 months.
Food-borne and wound botulism:
Symptoms of food-borne botulism develop suddenly, usually 18 to 36 hours after toxins enter the body, although symptoms can start as soon as 4 hours or as late as 8 days after ingesting the toxins. The more toxin ingested, the sooner people become sick.
The first symptoms of food-borne or wound botulism commonly result from loss of strength in the muscles of the face and head. These symptoms include dry mouth, blurred or double vision, drooping eyelids, difficulty focusing on nearby objects, slurred speech, and difficulty swallowing. Because swallowing is difficult, food or saliva may be inhaled (aspirated) into the lungs, causing choking or gagging and increasing the risk of pneumonia (see Aspiration Pneumonia). The pupils of the eyes do not constrict normally when exposed to light during an eye examination. However, in food-borne botulism, the first symptoms are often nausea, vomiting, stomach cramps, and diarrhea. People who have wound botulism do not have any digestive symptoms.
Nerve damage by the toxins affects muscle strength but not sensation. Typically, after strength is lost in the muscles of the face and head, strength is then gradually lost in the muscles of the arms and legs and the muscles involved in breathing. Muscles become progressively weaker. The resulting breathing problems may be life threatening. Many people become constipated.
The mind usually remains clear.
In about 90% of infants with infant botulism, constipation is the first symptom. Then the muscles become paralyzed, beginning in the face and head and eventually reaching the arms, legs, and muscles involved in breathing. Eyelids droop, crying is weak, drooling may increase, infants are less able to suck, and their face loses its expression. Problems range from being tired and feeding slowly to losing a substantial amount of muscle tone and having difficulty breathing. When infants lose muscle tone, they may feel abnormally limp.
Doctors suspect botulism based on symptoms. However, other disorders can cause similar symptoms, so additional information is needed.
Electromyography (stimulating muscles and recording their electrical activity—see Electromyography and Nerve Conduction Studies) may be useful. In most cases of botulism, it shows abnormal muscle responses after electrical stimulation.
For food-borne botulism, a likely food source provides a clue. For example, when botulism occurs in two or more people who ate the same food prepared in the same place, the diagnosis is clearer. The diagnosis is confirmed when the toxins are detected in the blood or when the bacteria or toxins are detected in a sample of stool. Toxins may also be identified in food that was eaten.
For wound botulism, doctors ask whether people have had an injury that broke the skin. Doctors may inspect the skin for puncture marks suggesting use of an illicit drug. The diagnosis is confirmed when the toxins are detected in the blood or when the bacteria are detected in a culture of tissue from the wound.
Detecting the bacteria or the toxins in a sample of an infant's stool confirms the diagnosis of infant botulism.
Sometimes determining whether botulism developed from a wound or from food is impossible.
The spores of Clostridium botulinum are highly resistant to heat and may survive boiling for several hours. However, the toxins are readily destroyed by heat. Stored foods can cause botulism if they were inadequately cooked before they were stored. The bacteria can produce some toxins at temperatures as low as 37.4° F (3° C), a typical refrigerator temperature, so refrigerating food does not automatically make it safe.
The following measures can help prevent food-borne botulism:
If people are unsure whether a can should be discarded, they can check it when they start to open it. Before making the first puncture, they can place a few drops of water in the spot to be punctured. If water is expelled rather than sucked into the can when the can is punctured, the can is contaminated and should be discarded.
Any food that may be contaminated should be disposed of carefully. Even tiny amounts of toxins ingested, inhaled, or absorbed through the eye or a break in the skin can cause serious illness. Skin contact should be avoided as much as possible, and hands should be washed immediately after handling the food.
If a wound becomes infected, promptly seeking medical attention can reduce the risk of wound botulism.
Researchers and other people who work with the bacteria or its toxin are immunized.
People who may have botulism should go to the hospital immediately. Laboratory tests to confirm the diagnosis may be done, but treatment cannot be delayed until the results are known. To help eliminate any unabsorbed toxin, doctors may give activated charcoal by mouth or through a tube passed through the nose or mouth and into the stomach.
Vital signs (pulse, breathing rate, blood pressure, and temperature) are measured often. If breathing problems begin, people are transferred to an intensive care unit and may be temporarily placed on a ventilator. Such treatment has reduced the percentage of deaths due to botulism from about 70% in the early 1900s to less than 10%.
A substance that blocks the action of the toxins (antitoxin) is given as soon as possible after botulism has been diagnosed. It is most likely to help if given within 72 hours of when symptoms begin. The antitoxin may slow or stop further physical deterioration, so that the body can heal itself over a period of months. However, the antitoxin cannot undo damage already done. Also, some people have a serious allergic (anaphylactic) reaction to the antitoxin, which is derived from horse serum, or develop serum sickness (see Treatment). The horse serum antitoxin is not recommended for infant botulism. Instead, doctors use botulism immune globulin derived from the blood of people immunized against botulism.
People may need to be fed through a tube inserted into a vein (intravenously). Infants may need to be fed through a thin plastic feeding tube (a nasogastric tube) passed through the nose and down the throat.
If people have wound botulism, the wound is thoroughly cleaned, and dead tissue is removed. Then antibiotics, such as penicillin and metronidazole, are given by injection.
Some people who recover from botulism feel tired and are short of breath for years afterward. They may need long-term physical therapy.
Last full review/revision December 2014 by Michael Rubin, MDCM