Botulinum Toxin: A Poison That Can Heal

by Food and Drug Administration (FDA)

Botulinum toxin can heal as well as harm. The bacterial toxin that can paralyze and kill if consumed in contaminated food is now safely used, in a purified form, as a medicine to control certain conditions marked by involuntary muscle contractions.

The history and lethality of botulism would seem to make it an unlikely source for a curative substance. Although death rates from botulism poisoning are just a fraction of what they were 30 years ago, botulism continues to strike dozens of people every year — most of them infants, according to statistics from the national Centers for Disease Control and Prevention in Atlanta.

"Botulism is still lurking, and if our guard is not up, it will create a problem," says Richard C. Swanson, director of the Food and Drug Administration's division of emergency and investigational operations and one of the agency's representatives to the Inter-agency Botulism Research Coordinating Committee.

Botulism-causing Clostridium botulinum bacteria and their spores are everywhere. Prevalent in soil and marine sediments worldwide, their spores are often found on the surfaces of fruits and vegetables, and in seafood. The bacteria and spores themselves are harmless; the dangerous substance is the toxin produced by the bacteria when they grow. There are seven varieties of botulinum toxin, designated by the letters A through G.

Botulinum toxin is "the most poisonous substance known," says Stephen S. Arnon, M.D., head of the Infant Botulism Prevention Program at the California Department of Health Services. For this reason, anyone with symptoms of botulism should receive emergency treatment and public health officials should be notified to locate the source of the contamination and prevent other cases.

Once in the body, the toxin binds to nerve endings at the point where the nerves join muscles. This prevents the nerves from signaling the muscles to contract. The result is weakness and paralysis that descends from the cranium down, affecting, among other things, the muscles that regulate breathing.

Before the development of mechanical ventilators, the respiratory paralysis caused by botulism claimed many more victims than it does today. Between 1910 and 1919, for example, the death rate from botulism was 70 percent. By the 1980s the rate had dropped to 9 percent, and in 1993 it was less than 2 percent. But recovery is still slow; assuming the patient receives proper care to ensure continued breathing, recovery occurs only when the affected nerves grow new endings, a process that can take several months, although the length of time varies greatly from case to case.

If botulism is caught in the early stages, injection of an antitoxin made from horse serum can lessen the severity of disease by neutralizing the toxin that has not yet bound to nerve endings. But because of the risk of serious side effects such as anaphylaxis, a life-threatening allergic reaction, and serum sickness (an unpredictable allergic reaction to the horse serum, which can lead to anaphylaxis), the equine antitoxin cannot always be used, and it is never given to infants.

The condition in which C. botulinum spores germinate and toxin is produced — absence of oxygen, low acidity levels, and temperatures between 40 and 120 degrees Fahrenheit (4.5 to 49 degrees Celsius) — can easily develop in improperly stored home-cooked or commercial foods, as well as in canned foods that have not been prepared with proper canning procedures. Infant intestinal tracts, which haven't yet developed the full range of beneficial bacteria, can also present an environment inviting to C. botulinum toxin production, as can some deep wounds.

Three Types

There are three types of botulism poisoning, distinguished by the manner in which they are contracted: food-borne, wound and infant. In infant botulism the toxin is produced when C. botulinum spores germinate in the intestine. (Rarely, adults can acquire the disease this way.) In wound botulism, which is very rare, the toxin is produced by C. botulinum bacteria in an infected wound. In the food-borne form of the disease, the person ingests the toxin itself by eating food contaminated with it. Statistically, infant botulism, which was recognized in the mid-'70s, is the most common form of the disease. But the public still generally associates botulism with food poisoning in adults and children. The food-borne disease is the most avoidable form of botulism.

Symptoms usually develop within a day of eating the food, although they can take up to 10 days to manifest. Apart from weakness and paralysis, common complaints include fatigue, dry mouth, and difficulty swallowing. Unfortunately, doctors sometimes misdiagnose the symptoms as Guillain-Barré syndrome, stroke, intoxication, or a handful of other conditions. For this reason, federal health officials suspect that botulism poisoning is underdiagnosed.

Home Canning

One of the most common culprits in food-borne botulism is home-canned food, especially vegetables such as asparagus, green beans, and peppers. More than 90 percent of food-borne botulism outbreaks between 1976 and 1985 were due to home-processed foods.

"If you home-can products, make sure you use proper equipment, proper containers to can in, and use the up-to-date process," Swanson advises. U.S. Department of Agriculture home canning guidelines are available from county extension offices. One basic recommendation is to cook food to be canned in pressure cookers because they can maintain temperatures high enough (above 212 F, or 100 C) for 10 minutes to kill the spores, which are remarkably heat-resistant.

Foods cooked at home should not be left at temperatures between 40 F and 140 F (4.5 C to 60 C) for more than four hours. Toxin that may have formed can readily be destroyed by boiling the food for 10 minutes.

Commercial foods have also been involved in botulism outbreaks. Some outbreaks have been attributed to improperly handled food, such as potato salad, served in restaurants. But many commercial food outbreaks are due to consumer mishandling, such as disregarding labels that indicate the food should be refrigerated. Some food companies acidify their products or lower their moisture content as an extra precautionary measure in case the refrigeration warning is not heeded. Consumers can best protect themselves by reading the labels and following the storage instructions, Swanson says, and by discarding rusty, swollen or otherwise damaged cans.

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.