Botulism
Botulism is a rare and potentially fatal illness caused by botulinum toxin, which is produced by the bacterium Clostridium botulinum. The disease begins with weakness, blurred vision, feeling tired, and trouble speaking. This may then be followed by weakness of the arms, chest muscles, and legs. Vomiting, swelling of the abdomen, and diarrhea may also occur. The disease does not usually affect consciousness or cause a fever.
Botulism can occur in several ways. The bacterial spores which cause it are common in both soil and water and are very resistant. They produce the botulinum toxin when exposed to low oxygen levels and certain temperatures. Foodborne botulism happens when food containing the toxin is eaten. Infant botulism instead happens when the bacterium develops in the intestines and releases the toxin. This typically only occurs in children less than one year old, as protective mechanisms against development of the bacterium develop after that age. Wound botulism is found most often among those who inject street drugs. In this situation, spores enter a wound, and in the absence of oxygen, release the toxin. The disease is not passed directly between people. Its diagnosis is confirmed by finding the toxin or bacteria in the person in question.
Prevention is primarily by proper food preparation. The toxin, though not the spores, is destroyed by heating it to more than for longer than five minutes. The clostridial spores can be destroyed in an autoclave with moist heat or dry heat or by irradiation. The spores of group I strains are inactivated by heating at 121°C for 3 minutes during commercial canning. Spores of group II strains are less heat-resistant, and they are often damaged by 90°C for 10 minutes, 85°C for 52 minutes, or 80°C for 270 minutes; however, these treatments may not be sufficient in some foods. Honey can contain the organism, and for this reason, honey should not be fed to children under 12 months. Treatment is with an antitoxin. In those who lose their ability to breathe on their own, mechanical ventilation may be necessary for months. Antibiotics may be used for wound botulism. Death occurs in 5 to 10% of people. Botulism also affects many other animals. The word is from Latin botulus, meaning 'sausage'.
Signs and symptoms
The muscle weakness of botulism characteristically starts in the muscles supplied by the cranial nerves—a group of twelve nerves that control eye movements, the facial muscles and the muscles controlling chewing and swallowing. Double vision, drooping of both eyelids, loss of facial expression and swallowing problems may therefore occur. In addition to affecting the voluntary muscles, it can also cause disruptions in the autonomic nervous system. This is experienced as a dry mouth and throat, postural hypotension, and eventually constipation. Some of the toxins also precipitate nausea, vomiting, and difficulty with talking. The weakness then spreads to the arms and legs.Severe botulism leads to reduced movement of the muscles of respiration, and hence problems with gas exchange. This may be experienced as dyspnea, but when severe can lead to respiratory failure, due to the buildup of unexhaled carbon dioxide and its resultant depressant effect on the brain. This may lead to respiratory compromise and death if untreated.
Clinicians frequently think of the symptoms of botulism in terms of a classic triad: bulbar palsy and descending paralysis, lack of fever, and clear senses and mental status.
Infant botulism
Infant botulism was first recognized in 1976, and is the most common form of botulism in the United States. Infants are susceptible to infant botulism in the first year of life, with more than 90% of cases occurring in infants younger than six months. Infant botulism results from the ingestion of the C. botulinum spores, and subsequent colonization of the small intestine. The infant gut may be colonized when the composition of the intestinal microflora is insufficient to competitively inhibit the growth of C. botulinum and levels of bile acids are lower than later in life.The growth of the spores releases botulinum toxin, which is then absorbed into the bloodstream and taken throughout the body, causing paralysis by blocking the release of acetylcholine at the neuromuscular junction. Typical symptoms of infant botulism include constipation, lethargy, weakness, difficulty feeding, and an altered cry, often progressing to a complete descending flaccid paralysis. Although constipation is usually the first symptom of infant botulism, it is commonly overlooked.
Honey is a known dietary reservoir of C. botulinum spores and has been linked to infant botulism. For this reason, honey is not recommended for infants less than one year of age. Most cases of infant botulism, however, are thought to be caused by acquiring the spores from the natural environment. Clostridium botulinum is a ubiquitous soil-dwelling bacterium. Many infant botulism patients have been demonstrated to live near a construction site or an area of soil disturbance.
Infant botulism has been reported in 49 of 50 US states, and cases have been recognized in 26 countries on five continents.
Complications
Infant botulism has no long-term side effects.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 7% due to improved supportive care. A patient with severe botulism may require mechanical ventilation as well as intensive medical and nursing care, sometimes for several months. The person may require rehabilitation therapy after leaving the hospital.
Cause
Clostridium botulinum is an anaerobic, Gram-positive, spore-forming rod. Botulinum toxin is one of the most powerful known toxins: about one microgram is lethal to humans when inhaled. It acts by blocking nerve function through inhibition of the excitatory neurotransmitter acetylcholine's release from the presynaptic membrane of neuromuscular junctions in the somatic nervous system. This causes paralysis. Advanced botulism can cause respiratory failure by paralysing the muscles of the chest; this can progress to respiratory arrest. Furthermore, acetylcholine release from the presynaptic membranes of muscarinic nerve synapses is blocked. This can lead to a variety of autonomic signs and symptoms described above.In all cases, illness is caused by the botulinum toxin which the bacterium C. botulinum produces in anaerobic conditions and not by the bacterium itself. The pattern of damage occurs because the toxin affects nerves that fire at a higher frequency first.
Mechanisms of entry into the human body for botulinum toxin are described below.
Colonization of the gut
The most common form in Western countries is infant botulism. This occurs in infants who are colonized with the bacterium in the small intestine during the early stages of their lives. The bacterium then produces the toxin, which is absorbed into the bloodstream. The consumption of honey during the first year of life has been identified as a risk factor for infant botulism; it is a factor in a fifth of all cases. The adult form of infant botulism is termed adult intestinal toxemia, and is exceedingly rare.Food
Toxin that is produced by the bacterium in containers of food that have been improperly preserved is the most common cause of food-borne botulism. Fish that has been pickled without the salinity or acidity of brine that contains acetic acid and high sodium levels, as well as smoked fish stored at too high a temperature, presents a risk, as does improperly canned food.Food-borne botulism results from contaminated food in which C. botulinum spores have been allowed to germinate in low-oxygen conditions. This typically occurs in improperly prepared home-canned food substances and fermented dishes without adequate salt or acidity. Given that multiple people often consume food from the same source, it is common for more than a single person to be affected simultaneously. Symptoms usually appear 12–36 hours after eating, but can also appear within 6 hours to 10 days.
No withdrawal periods have been established for cows affected by botulism. Lactating cows injected with various doses of botulinum toxin C have not resulted in detectable botulinum neurotoxin in milk produced. Using mouse bioassays and immunostick ELISA tests, botulinum toxin was detected in whole blood and serum but not in milk samples, suggesting that botulinum type C toxin does not enter milk in detectable concentrations. Cooking and pasteurization denatures botulinum toxin but does not necessarily eliminate spores. Botulinum spores or toxins can find their way into the dairy production chain from the environment. Despite the low risk of milk and meat contamination, the protocol for fatal bovine botulism cases appears to be incineration of carcasses and withholding any potentially contaminated milk from human consumption. It is also advised that raw milk from affected cows should not be consumed by humans or fed to calves.
There have been several reports of botulism from pruno wine made of food scraps in prison. In a Mississippi prison in 2016, prisoners illegally brewed alcohol that led to 31 cases of botulism. The research study done on these cases found the symptoms of mild botulism matched the symptoms of severe botulism, though the outcomes and progression of the disease were different.