Botulism

• Botulism is poisoning by botulinum neurotoxin, one of the most potent toxins known. It is produced mainly by the anaerobic bacterium Clostridium botulinum, and occasionally by Clostridium baratii and Clostridium butyricum. ^[4]
• The toxin enters nerve endings and cuts the SNARE proteins that let vesicles release acetylcholine. Without acetylcholine the muscles and autonomic fibres stop working, giving a flaccid paralysis.
• The illness is always descending and symmetric: cranial nerve palsies (double vision, drooping eyelids, difficulty swallowing, slurred speech) come first, then weakness of the neck, arms, trunk and legs, and finally the breathing muscles.
• There is no fever, no numbness and no confusion. The patient's mind stays clear, which is a vital clue.
• It is a medical emergency. If you suspect it, call the public health service for antitoxin immediately and do not wait for laboratory proof. Watch breathing closely and be ready to ventilate.

By the end of this page you should be able to:

1. Explain how botulinum neurotoxin produces paralysis, and why its effects last.
2. List the five forms of botulism, identify who gets each, and describe how each form is acquired.
3. Recognise the clinical picture of botulism and distinguish it from Guillain-Barre syndrome and myasthenia gravis.
4. Plan the immediate care of a suspected case, including airway, antitoxin use, wound management and intensive care.
5. Order the correct confirmatory tests and route specimens through public health.
6. Describe prevention and the steps needed where resources are limited.

The five recognised forms differ only by how the toxin reaches the patient^[2]. All share the same final mechanism and the same dangerous outcome if missed.

• Foodborne botulism, from eating food that already contains toxin.
• Infant botulism, from swallowed spores that germinate in an infant's intestines and make toxin there.
• Wound botulism, from spores that germinate in a contaminated wound and make toxin inside the body.
• Iatrogenic botulism, from too much therapeutic or cosmetic botulinum toxin being injected.
• Adult intestinal colonisation (adult intestinal toxemia), a very rare form in which spores germinate in an adult's gut, resembling infant botulism.

Adult intestinal colonisation has been recognised in only a handful of people, usually those with a serious bowel condition. Its mechanism is suspected to be the same as infant botulism.^[3]

Botulism is rare, and most people will never encounter it. All forms are medical emergencies and any one of them can be fatal.^[2] About 5 of every 100 people with botulism die. Death comes from respiratory failure or from the consequences of prolonged paralysis.^[1] Patients who survive may have fatigue and shortness of breath for years.^[1]

Serotypes A, B, E and F are the ones that cause human disease. Type A, which is the commonest cause of foodborne and wound botulism in many places, produces the longest paralysis because its light chain is the hardest for the nerve cell to destroy. Type E, which is often linked to fish and marine products, acts for a much shorter time.^[4]

The bacterium Clostridium botulinum is a Gram-positive, spore-forming anaerobe. It thrives in low-oxygen, low-acid, low-salt and low-sugar surroundings with sufficient water and a pH of 4.6 or higher. Its dormant spores are found in soil, in aquatic sediment, in dust and on many foods. They survive extreme heat, drying and chemicals, and germinate when conditions suit them.^[4]

Different genetic groups carry the toxin gene: human disease comes from groups I and II, while groups III and IV mainly affect animals.^[4] Toxin can also be made by Clostridium baratii and Clostridium butyricum. These organisms are not C. botulinum on culture yet still cause botulism, which matters when a stool culture is read.^[2]

Risk varies by form^[2][3].

• Foodborne: improperly home-canned, preserved or fermented foods, especially low-acid foods such as vegetables, meats, poultry, fish and seafood, figs and some tomatoes; pruno, a homemade alcohol made in some prisons; garlic or herbs stored too long in oil; baked potatoes wrapped in foil held warm; fermented fish and marine animals in some communities; occasionally store-bought foods.
• Wound: injecting illicit drugs, notably black tar heroin; traumatic wounds and crush injuries; surgery; any wound that is low in oxygen, even one that does not look infected.
• Infant: no single preventable cause. The spores are in soil and dust and can be found on floors, carpets and counters even after cleaning.
• Iatrogenic: unapproved products, excessive doses, or injection by untrained providers of botulinum toxin for cosmetic or medical use.
• Adult intestinal: serious health conditions that disturb the gut.

Infant botulism occurs in young infants whose gut flora is immature. Babies under 1 year must never be given honey or products containing honey, because honey can carry the spores and their immature gut cannot stop the spores from germinating.^[3]

Every form of botulism ends in the same place: the junction between a nerve and its target. The toxin is a protein of about 150 kilodaltons, made of two chains. The heavy chain binds the nerve ending and pulls the toxin inside. The light chain is a zinc-dependent enzyme that cuts the SNARE proteins (SNAP-25, synaptobrevin or VAMP, and syntaxin). These proteins are the machinery that fuses a vesicle to the nerve membrane and releases acetylcholine. Once they are cut, the vesicle cannot empty and the nerve can no longer signal the muscle.^[4]

Because acetylcholine is the messenger at every neuromuscular junction and at parasympathetic autonomic synapses, the loss is both motor and autonomic: flaccid weakness, dry mouth, constipation, and problems with the pupils and the heart rate.^[4]

The paralysis descends because the cranial nerves are affected before the limbs. It is symmetric because the toxin is in the blood and reaches both sides equally. Sensation is spared because the sensory nerves do not depend on acetylcholine release in this way. The mind stays fully clear, because the toxin does not cross into the central nervous system and the person remains awake and aware while wholly paralysed. Fever is absent unless there is an infected wound or another illness, because the paralysis is not inflammation. It is chemical.

The toxin's effects last a long time. The light chain persists inside the nerve cell and keeps cutting SNARE proteins until the nerve can build new ones. Even after antitoxin is given, recovery takes weeks to months and follows the regrowth of new neuromuscular connections.^[1][4] Type A lasts for months; type E for weeks.^[4] In untreated or late cases, mechanical ventilation may be needed for several months.^[4]

Patients look ill and weak but are fully conscious, often frightened, and able to feel everything. The weakness is flaccid and the reflexes are reduced or absent. The illness is described as descending because each stage passes from the head downwards, and invariable because it always follows the same order.

These usually appear first, often within hours to a couple of days of exposure.

• Ocular: double vision, blurred vision, drooping upper eyelids (ptosis), and difficulty moving the eyes.
• Facial and bulbar: slurred speech (dysarthria), difficulty swallowing (dysphagia), dry mouth, weak jaw and facial expression, a weak and altered cry in an infant.
• Autonomic: constipation, urinary retention, tachycardia, pupils that are dilated or react sluggishly, dry eyes.

Foodborne cases often start with nausea, vomiting, abdominal pain and diarrhoea, but these are brief; the neurological picture dominates.^[1]

Weakness spreads to the neck, the arms, the trunk and the legs. Deep tendon reflexes fall. The breathing muscles are next: the diaphragm and intercostal muscles weaken, producing respiratory distress and respiratory failure without warning. Mechanical ventilation may be needed for weeks to months in severe cases.^[1][4]

Every form shows the same pattern. Foodborne illness is more likely to begin with gastric upset. Wound botulism begins with cranial nerve palsies alone, a week or two after an injury. Infant botulism presents as poor feeding, constipation, a weak cry, a flattened face and general floppiness. A classic scene is several people who shared a meal or a jar, with some, or many, developing the same descending weakness while one remains well.

Botulism does not produce fever (except where the wound or another infection does), numbness, tingling, back pain or altered consciousness. The patient can describe everything. These negative findings matter as much as the positive ones, because they separate botulism from most of its mimics.

Botulism is most often misdiagnosed as Guillain-Barre syndrome, Miller-Fisher syndrome or myasthenia gravis, or as a stroke, meningitis, sepsis, a poisoning or a drug overdose.^[1] The fuller differential list includes bacterial or chemical food poisoning, cerebrovascular accident, chemical intoxication, congenital myopathy, electrolyte imbalance, Lambert-Eaton myasthenic syndrome, Leigh syndrome, mushroom poisoning, poliomyelitis, Reye syndrome, tick paralysis, Werdnig-Hoffmann disease and West Nile virus, among others.^[1]

Helpful clinical comparisons:

• Guillain-Barre syndrome usually ascends (legs first) or is areflexic with sensory loss; botulism descends and spares sensation. The albuminocytological dissociation of cerebrospinal fluid in Guillain-Barre is not seen in botulism.
• Myasthenia gravis fluctuates and improves with rest or with an anticholinesterase (edrophonium, the Tensilon test); a normal Tensilon test helps to separate botulism from myasthenia, although borderline positives can occur in botulism. Pupils are often normal in myasthenia but affected in botulism.
• Lambert-Eaton syndrome also reduces acetylcholine release and causes dry mouth; it is a paraneoplastic presynaptic disorder that improves briefly after use, unlike botulism, and it does not descend from the cranial nerves.
• Stroke is sudden, one-sided and lacks the bilateral cranial-nerve onset; normal brain imaging helps rule it out.^[1]

The diagnosis is clinical. Public health and treatment must not wait for the laboratory. Routine blood tests are usually unremarkable.^[1]

Bedside clues that argue for botulism are a descending symmetric flaccid paralysis starting with the cranial nerves, single breath counts falling, an unremarkable routine screen, clear consciousness, no fever and no sensory loss.^[1] Intubation should be considered before overt respiratory failure, because weakening can be rapid and silent.

Confirmation is made by showing botulinum toxin in serum, stool, or food, or by culturing a toxin-producing species of Clostridium (C. botulinum, C. baratii or C. butyricum) from stool or a wound.^[1] These tests are performed by the state or national public health laboratory and often take several days; results may not arrive for up to five days, so clinical judgement leads treatment.^[1]

Because the toxin assay is insensitive later in the illness, a negative test does not exclude botulism. In foodborne cases serum toxin is found more often early, and in wound cases less so; stool culture is more useful. In infant botulism the diagnosis is often confirmed by finding the organism or toxin in the stool, and sometimes neuromuscular studies are used when tests are pending. Routine infection tests such as blood cultures and imaging are taken mainly to exclude the mimics; a normal computed tomography or magnetic resonance image helps to rule out a stroke.^[1]

Take blood cultures if a wound is present or the picture could be endocarditis or sepsis, and send the suspected food if any remains. State public health will advise on specimen collection and transport.

Most of the danger comes from the breathing muscles. Monitor respiratory function continuously and intubate and ventilate before obvious failure, because deterioration can be sudden. In severe cases ventilator support may be needed for weeks to months.^[1][4] Provide meticulous attention to bladder and bowel care and to the prevention of urinary infection, deep-vein thrombosis and pressure ulcers. Evaluate for and treat dry eyes and dry mouth, and anticipate copious oral secretions.^[1]

Patients are mentally intact throughout. Establish a system that lets them communicate, explain every procedure beforehand, and assess for anxiety and depression with psychological support, music and massage therapy, and family involvement.^[1]

Antitoxin does not heal the damage already done. It binds toxin that is still circulating and stops further paralysis, so it must be given as early as possible, ideally within the first 24 to 48 hours after symptoms begin.^[4] It is ineffective against toxin already inside nerve cells.^[4]

• Heptavalent antitoxin (BAT), an equine product covering serotypes A, B, C, D, E, F and G, is used for adults and children over about 12 months with symptomatic botulism after documented or suspected exposure. It is given intravenously.^[6]
• BabyBIG, human botulism immune globulin against types A and B, is used for infants under 12 to 15 months. It is ordered through the Infant Botulism Treatment and Prevention Program, whose physicians consult without obligation to order. Treatment promptly ends toxemia and lets nerve regeneration begin.^[5]

Neither product reverses paralysis already established. Both work best early in the illness.^[1]

Along with antitoxin, treat the wound: debride to remove the source of toxin-producing bacteria and give antibiotic therapy. Antibiotics are not part of the treatment for other forms, because they may increase toxin release from dying bacteria in the gut.^[1]

Recovery follows the regeneration of new neuromuscular connections, a process taking weeks to months even after antitoxin is given. Start speech, physical and occupational therapy as soon as possible.^[1]

• Respiratory failure, which is the usual cause of death.
• Aspiration pneumonia from bulbar weakness.
• Deep-vein thrombosis and pressure ulcers from immobility.
• Autonomic instability, including hypotension, tachycardia and constipation.
• Secondary wound infection in wound botulism.
• Prolonged dependence on intensive care and mechanical ventilation.
• Psychological distress from prolonged wakeful paralysis.
• Long-term fatigue and breathlessness in survivors.^[1]

With antitoxin and modern intensive care, about 5 of every 100 people with botulism still die.^[1] Most of those who survive improve, but the fatigue and breathlessness may linger for years and rehabilitation can be long. In untreated or late cases mechanical ventilation may be needed for months. Early antitoxin is the single most important modifiable factor.

Foodborne botulism can usually be prevented by careful food handling.

• Follow safe home-canning instructions and pay special attention to low-acid foods (all fresh vegetables, figs, meats, poultry, fish, seafood, and some tomatoes); pressure canning is the only recommended method for low-acid foods.
• Store canned food properly and refrigerate after opening.
• Boil some foods for 10 minutes before eating them (adding 1 minute for every additional 1,000 feet of elevation): home-canned tomatoes, foods containing them, all low-acid home-canned foods, and all home-fermented Alaska Native foods. ^[3]
• Refrigerate oils made with garlic or herbs and discard them after 4 days. ^[3]
• Keep baked potatoes wrapped in foil at 140 degrees Fahrenheit or hotter until served, or refrigerate them with the foil loosened. ^[3]
• Do not drink pruno, a homemade alcohol made in some jails and prisons.
• When in doubt, throw it out: never taste food whose safety is uncertain.
• Never give honey or honey products to infants under 1 year.
• Prevent wound botulism by not injecting illicit drugs and by keeping wounds clean and seeking care quickly for infected wounds.
• Use licensed, trained providers and approved products for any botulinum toxin injection, and verify licensing.

Alaska Native traditional fermented foods have a long association with foodborne botulism, and prevention there combines traditional preparation methods with modern practice.^[3]

Infants show a different, more subtle presentation: constipation (often the first sign), poor feeding, a flat expression, a weak and altered cry, drooping eyelids, sluggish pupils and general hypotonia. The diagnosis is easily missed as sepsis or meningitis. Treatment is BabyBIG via the Infant Botulism Treatment and Prevention Program, and honey products must be avoided entirely under 1 year.^[3][5]

Older adults and people with chronic gut disease may be at higher risk of the rare adult intestinal form. People dependent on injected drugs are at high risk of wound botulism and need harm-reduction and wound care messages. Pregnant patients require individualised advice from specialist teams. Other countries have their own infant botulism programmes and antitoxin access routes.

Botulism is a notifiable disease. Physicians must promptly notify the state or national health department of every suspected case, and laboratories must notify them of all confirmed cases. Suspected food samples and specimens go through the health department laboratory, and confirmation can take days.^[1]

Notification is not paperwork. It is the mechanism by which antitoxin is released, other cases are found, the food source is identified and recalled, and a possible outbreak is stopped. In the United States the public health department arranges expert clinical consultation and, when needed, releases antitoxin; if the department cannot be reached, call the CDC Clinical Botulism Service around the clock. Infant cases go to the Infant Botulism Treatment and Prevention Program.^[1]

Where intensive care, antitoxin or advanced testing are scarce, the priorities are simple, cheap and life-saving.

• Recognise the pattern early. A person who is mentally clear but cannot swallow, close their eyes or hold their head up, and who then becomes breathless, is likely to have botulism. Any unexplained descending flaccid paralysis starting with the cranial nerves should trigger this diagnosis.
• Protect the airway before it fails. Counting the breaths, watching oxygen saturation and measuring bedside vital capacity or negative inspiratory force, where possible, prevent a sudden arrest. Have bag-mask ventilation ready and move the patient to a place with mechanical ventilation as early as possible.
• Rehydrate and nourish. Bulbar weakness prevents eating and drinking safely; use a nasogastric or orogastric tube when the airway is protected, and manage constipation and urinary retention gently.
• Antibiotics and debridement for wound botulism when antitoxin is delayed or unavailable; at least clean and open the wound.
• Seek antitoxin aggressively, through whichever regional or national channel exists; neighbouring countries and international public health bodies can sometimes supply it.
• Ask about a shared food and alert public health so the source can be found and recalled, preventing more cases.
• Send specimens through the highest level of laboratory available and do not delay treatment while waiting.
• Use simple preventive advice that costs nothing: safe canning, boiling low-acid canned foods, never feeding honey to infants, keeping wounds clean, and never tasting food of doubtful safety.

Related topics to read alongside this page include dysphagia, Guillain-Barre syndrome, myasthenia gravis, food poisoning and infectious diarrhoea, wound infection, intensive care respiratory failure, cranial nerve palsies, and public health notification of notifiable diseases.

• Botulism is poisoning by botulinum neurotoxin, one of the most lethal substances known. It attacks nerves, not muscles, by cutting the proteins that release acetylcholine.
• There are five forms: foodborne, infant, wound, iatrogenic and adult intestinal colonisation. All are medical emergencies and all can kill.
• The illness is a descending, symmetric, flaccid paralysis that starts with the cranial nerves: double vision, ptosis, difficulty swallowing and slurred speech, then weakness of the limbs and trunk, then respiratory failure.
• There is no sensory loss and no change in consciousness. The patient remains awake and aware. Fever is absent unless another infection is present.
• The mind stays clear; dry mouth, constipation and tachycardia reflect autonomic involvement.
• It is most often mistaken for Guillain-Barre syndrome, Miller-Fisher syndrome or myasthenia gravis. A Tensilon test that does not help and imaging that does not show a stroke support botulism.
• Diagnosis is clinical. Do not wait for the laboratory to treat.
• Management is airway first, then antitoxin, plus intensive care. Adults get heptavalent antitoxin (BAT) early; infants get BabyBIG. Neither reverses established paralysis.
• Wound botulism also needs debridement and antibiotics.
• Recovery takes weeks to months, even after antitoxin.
• About 5 of every 100 patients die; fewer with early treatment.
• Prevention centres on safe food handling, never giving honey to infants, and avoiding injected drugs. Public health notification is mandatory and makes treatment and prevention possible.
• Survivors may have fatigue and breathlessness for years.