Human botulism is a serious but relatively rare disease. The disease is an intoxication caused by extremely potent toxins preformed in foods. The toxins are produced by the bacterium Clostridium botulinum. Person to person transmission of botulism does not occur. There are seven recognized types of botulism. Four of these (types A, B, E and rarely F) cause human botulism. Types C, D and E cause illness in mammals, birds and fish. The sporulated form of the bacterium is commonly found in soils, aquatic sediments and fish. The spores are heat-resistant. Under anaerobic conditions, botulinum spores can germinate, and the bacterium grow and produce the toxin. Ingestion of the toxin present in improperly prepared food is dangerous and may be fatal. Botulism is mainly a foodborne intoxication, but it can also be transmitted through wound infections or intestinal infection in infants.
The symptoms are not caused by the organism itself but by the toxin that the bacterium releases. They usually appear within 12 to 36 hours (within a minimum and maximum range of four hours to eight days) after exposure. Incidence of botulism is low, but the mortality rate is high if treatment is not immediate and proper. The disease can be fatal in 5 to 10% of cases.
The characteristic early symptoms and signs are marked fatigue, weakness and vertigo, usually followed by blurred vision, dry mouth and difficulty in swallowing and speaking. Vomiting, diarrhea, constipation and abdominal swelling may occur. The disease can progress to weakness in the neck and arms, after which the respiratory muscles and muscles of the lower body are affected. The paralysis may make breathing difficult. There is no fever and no loss of consciousness. Similar symptoms usually appear in individuals who shared the same food. Most cases recover, if given proper and immediate treatment, including prompt diagnosis, early administration of antitoxin and intensive respiratory care. Foodborne botulism occurs when the organism Colstridium botulinum is allowed to grow and produce toxin in food which is then eaten without sufficient cooking to inactivate the toxin. Clostridium botulinum is an "anaerobic bacterium," which means it can only grow in the absence of oxygen. Therefore, the growth of the bacteria and the formation of toxin tend to occur in products with low oxygen content and the right combination of storage temperature and preservative parameters. This happens most often in lightly preserved foods such as fermented, salted or smoked fish and meat products and in inadequately processed home canned or home bottled low acid foods such as vegetables. The food traditionally implicated differs between countries and will reflect local eating habits and food preservation procedures. Occasionally, commercially prepared foods are involved.
The different types of intoxication due to the botulinum toxin are:
- The botulinal toxin has been found in a variety of foods, including low-acid preserved vegetables, such as green beans, spinach, mushrooms and beets; fish, including canned tuna, fermented, smoked and salted fish; and meat products, such as ham, chicken and sausage. The toxin is destroyed by normal cooking processes (heating at >85°C [185°F] for five minutes or boiling for a few minutes). Clostridium botulinum will not grow, and therefore the toxin will not be formed in acidic foods (pH less than 4.6). However, the low pH will not inactivate any preformed toxin.
- Inhalation botulism, following inhalation of the toxin (in an aerosol), has occurred in laboratory workers. In these cases, neurological symptoms may be the same as in foodborne botulism, but the incubation period might be longer.
- Waterborne botulism could theoretically also result from the ingestion of the pre-formed toxin. Since water treatment processes inactivate the toxin, the risk is considered low.
- Adverse effects of the pure toxin have been reported as a result of its medical and/or cosmetic use in patients.
- Infant botulism is rare. It occurs when infants ingest spores, which germinate to produce bacteria that reproduce in the gut and release the toxin. In most adults and children older than about six months, this would not happen because the natural defenses that develop over time prevent the germination and growth of Clostridium botulinum. Clinical symptoms in infants include constipation, loss of appetite, weakness, an altered cry and a striking loss of head control. Infant botulism has been associated with honey contaminated with botulism spores. Mothers are warned not to feed raw honey to their infants, as Clostridium botulinum spores in honey have in a few cases resulted in infant botulism.
- Botulism of undetermined origin usually involves adult cases where no food or wound source can be identified. It has been suggested that these cases are comparable to infant botulism and may occur when the normal gut flora has been altered as a result of surgical procedures or antibiotic therapy.
- Wound botulism is a rare disease and occurs when the spores get into an open wound and are able to reproduce in an anaerobic environment. The symptoms produced are similar to the foodborne form but may take up to two weeks to appear.
Prevention of botulism is based on good food preparation (particularly preservation) practices and hygiene. Botulism may be prevented by inactivation of the bacterial spores in heat-sterilized, canned products or by inhibiting growth in all other products. Commerical heat pasteurization (vacuum packed pasteurized products, hot smoked products) may not be sufficient to kill all spores and therefore, safety of these products must be based on preventing growth and toxin production. Refrigeration temperatures combined with salt content and/or acidic conditions will prevent the growth or formation of toxin. If exposure to the toxin via an aerosol is suspected, in order to prevent additional exposure to the patient and healthcare providers, the clothing of the patient must be removed and stored in plastic bags until it can be washed with soap and water. The patient must shower thoroughly.
Food and water samples associated with suspect cases must be obtained immediately, stored in proper sealed containers and sent to reference laboratories in order to help prevent further cases.
Antitoxin administration is indicated as soon as possible after clinical diagnosis has been made. Severe botulism cases require supportive treatment, especially mechanical ventilation, which may be required for weeks or months. Antibiotics are not required (except in the case of wound botulism). There is a vaccine against botulism, but it is used very rarely as its effectiveness is not fully evaluated, and it has side effects.
The bacterium Clostridium botulinum is the same bacterium that is used to produce Botox®, a pharmaceutical used as injections for clinical and cosmetic use. However, what is used in Botox® treatments is the purified and diluted A neurotoxin. Treatment is administered in the medical setting, tailored according to the needs of the patient and is usually well-tolerated. Occasionally, there may be some side effects.