Botulism is a rare but serious paralytic illness caused by a nerve toxin that is produced by the bacterium Clostridium botulinum. Clostridium botulinum is the name of a group of bacteria commonly found in soil. The bacteria are anaerobic, gram-positive, spore-forming rods that produce a potent neurotoxin. These rod-shaped organisms grow best in low oxygen conditions. The bacteria form spores that allow them to survive in a dormant state until exposed to conditions that can support their growth. The organism and its spores are widely distributed in nature. They occur in both cultivated and forest soils, bottom sediment of streams, lakes, and coastal waters, in the intestinal tracts of fish and mammals, and in the gills and viscera of crabs and other shellfish.
Foodborne botulism is a severe type of food poisoning caused by the ingestion of foods containing the potent neurotoxin formed during growth of the organism. The incidence of the disease is low, but the disease is of considerable concern because of its high mortality rate if not treated immediately and properly. Most of the 10 to 30 outbreaks that are reported annually in the United States are associated with inadequately processed, home-canned foods, but occasionally commercially produced foods are implicated as the source of outbreaks. Sausages, meat products, canned vegetables, and seafood products have been the most frequent vehicles for foodborne botulism.
Symptoms of Botulism
Classic symptoms of botulism include double vision, blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth, and muscle weakness. Infants with botulism appear lethargic, feed poorly, are constipated, and have a weak cry and poor muscle tone. 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. In foodborne botulism, symptoms generally begin 18 to 36 hours after consuming contaminated food, but they can occur as early as 6 hours or as late as 10 days after consumption.
Botulinum toxin causes flaccid paralysis by blocking motor nerve terminals at the myoneural junction. The flaccid paralysis progresses symmetrically downward, usually starting with the eyes and face, then moving to the throat, chest, and extremities. When the diaphragm and chest muscles become fully involved, respiration is inhibited and unless the patient receives treatment in time, death from asphyxia results.
Detection and Treatment of Botulism
Although botulism can be diagnosed by clinical symptoms alone, differentiation from other diseases may be difficult. The most direct and effective way to confirm the clinical diagnosis of botulism in the laboratory is to demonstrate the presence of toxin in the serum or feces of the patient or in the food the patient consumed. Currently, the most sensitive and widely used method for detecting toxin is the mouse neutralization test, which involves injecting serum or stool into mice and looking for signs of botulism. This test typically takes 48 hours. Culturing of specimens takes 5-7 days. Some cases of botulism may go undiagnosed because symptoms are transient or mild, or are misdiagnosed as Guillain-Barre Syndrome.
If diagnosed early, foodborne botulism can be treated with an antitoxin that 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 using enemas.
While botulism has been known to cause death due to respiratory failure, in the past 50 years the proportion of patients with botulism who die has fallen from about 50% to 8%. The respiratory failure and paralysis that occur with severe botulism may require a patient to be on a ventilator for weeks, plus intensive medical and nursing care. After several weeks, the paralysis slowly improves.
The types of foods implicated in botulism outbreaks vary according to food preservation and eating habits in different regions. Any food that is conducive to outgrowth and toxin production, that when processed allows spore survival, and is not subsequently heated before consumption, can be associated with botulism. Almost any type of food that is not very acidic (pH above 4.6) can support growth and toxin production by C. botulinum. Botulinal toxin has been demonstrated in a considerable variety of foods, such as canned corn, peppers, green beans, soups, beets, asparagus, mushrooms, ripe olives, spinach, tuna fish, chicken and chicken livers and liver pate, and luncheon meats, ham, sausage, stuffed eggplant, lobster, and smoked and salted fish.
Botulinum toxin is heat-labile, or unstable if heated to a certain temperature, and can be destroyed if heated and held at 80 degrees Centigrade (176 degrees Fahrenheit) for ten minutes or longer.