Botulism is a rare but serious paralytic illness caused by a nerve toxin that is produced by the bacterium Clostridium botulinum. Botulin is the toxin; clostridium botulinum is the bacterium that produces it. Botulin is the most potent known toxin, blocking nerve function and leading to respiratory and musculoskeletal paralysis.
There are three main kinds of botulism. Foodborne botulism is a form of food poisoning and is caused by eating foods that contain the botulism toxin. Wound botulism is caused by toxin produced from a wound infected with Clostridium botulinum. Infant botulism is caused by consuming the spores of the botulinum bacteria, which then grow in the intestines and release toxin. All forms of botulism can be fatal and are considered medical emergencies. Foodborne botulism can be especially dangerous as a public health problem because many people can be poisoned from a single contaminated food source.
In the United States an average of 110 cases of botulism are reported each year. Of these, approximately 25% are foodborne, 72% are infant botulism, and the rest are wound botulism. Outbreaks of foodborne botulism involving two or more persons occur during most years and usually are caused by eating contaminated home-canned foods. The number of cases of foodborne and infant botulism has changed little in recent years, but wound botulism has increased because of the use of black-tar heroin, especially in California.
Symptoms: Foodborne and Wound forms
Classic symptoms of botulism occur between 12-36 hours after uptake of the botulinum toxin, but they can occur as early as 6 hours or as late as 10 days. Those symptoms usually include dry mouth, difficulty swallowing, slurred speech, muscle weakness, double vision, vomiting, and severe diarrhea, along with a progressive muscle paralysis. These are all symptoms of the muscle paralysis caused by the bacterial toxin. If untreated, these symptoms may progress to cause paralysis of the arms, legs, trunk and respiratory muscles. Foodborne infection does not occur in healthy adults & children more than 1 year old. In all cases the toxin made by C. botulinum causes illness, not the bacterium itself.
Infant botulism is the most common form of the ailment in the United States. The mode of action of this form is through actual infection by germinating spores in the gut of an infant. Infection results in constipation, general weakness, loss of head control and difficulty feeding. Because of these symptoms, infant botulism is often referred to as "floppy baby syndrome". Many cases are caused by the under-pasteurization of honey and other foods (under-pasteurization occurs often in honey and other foods labelled as "organic" or "natural").
The leading explanation for why some infants become infected with C. botulinum, is that infants do not yet have sufficient numbers of resident microflora in their guts to competitively exclude C. botulinum. Thus, without competition, C. botulinum is able to establish itself in the gut of an infant.
Botulinum toxin blocks the release of acetylcholine from nerve endings thus arresting their function. This toxin is unstable to heating, or on prolonged exposure to oxygen, so poisoning generally occurs from the use of improperly bottled or canned foods: typical instances of botulism would be home-bottled preserves used in salads. An unusual example of botulism occurred in Britain in the unusually hot, dry summer of 1976, when river levels dropped so low in some areas that feeding swans accidentally ingested material from anaerobic layers in a river (normally out of their reach), and were struck by botulism symptoms.
Physicians may consider the diagnosis if the patient's history and physical examination suggest botulism. However, these clues are usually not enough to allow a diagnosis of botulism. Other diseases such as Guillain-Barré syndrome, stroke, and myasthenia gravis can appear similar to botulism, and special tests may be needed to exclude these other conditions. These tests may include a brain scan, spinal fluid examination, nerve conduction test (electromyography, or EMG), and a tension test for myasthenia gravis. The most direct way to confirm the diagnosis is to demonstrate the botulinum toxin in the patient's serum or stool by injecting serum or stool into mice and looking for signs of botulism. The bacteria can also be isolated from the stool of persons with foodborne and infant botulism.
The respiratory failure and paralysis that occur with severe botulism may require a patient to be on a breathing machine (ventilator) for weeks, plus intensive medical and nursing care. After several weeks, the paralysis slowly improves. If diagnosed early, foodborne and wound botulism can be treated with an antitoxin which blocks the action of toxin circulating in the blood. This can prevent patients from worsening, but recovery still takes many weeks. Physicians may try to remove contaminated food still in the gut by inducing vomiting or by using enemas. Wounds should be treated, usually surgically, to remove the source of the toxin-producing bacteria. Good supportive care in a hospital is the mainstay of therapy for all forms of botulism. Currently, antitoxin is not routinely given for treatment of infant botulism.
Furthermore each case of botulism is a potential public health emergency in that it is necessary to identify the source of the outbreak and ensure that all persons who have been exposed to the toxin have been identified, that no contaminated food remains, and that the outbreak is not the result of a deliberate terrorist attack.
Botulism can result in death due to respiratory failure. However, in the past 50 years the proportion of patients with botulism who die has fallen from about 50% to 8%. A patient with severe botulism may require a breathing machine as well as intensive medical and nursing care for several months. Patients who survive an episode of botulism poisoning may have fatigue and shortness of breath for years and long-term therapy may be needed to aid recovery.
Foodborne botulism has often been from home-canned foods with low acid content, such as asparagus, green beans, beets and corn. However, outbreaks of botulism have resulted from more unusual sources such as chopped garlic in oil, chile peppers, tomatoes, improperly handled baked potatoes wrapped in aluminum foil, and home-canned or fermented fish. Persons who do home canning should follow strict hygienic procedures to reduce contamination of foods. Oils infused with garlic or herbs should be refrigerated. Potatoes which have been baked while wrapped in aluminum foil should be kept hot until served or refrigerated. Because the botulism toxin is destroyed by high temperatures, persons who eat home-canned foods should consider boiling the food for 10 minutes before eating it to ensure safety. Because honey can contain spores of Clostridium botulinum and this has been a source of infection for infants, children less than 12 months old should not be fed honey. Honey is safe for persons 1 year of age and older. Wound botulism can be prevented by promptly seeking medical care for infected wounds and by not using injectable street drugs.