Botulism is an acute, progressive condition caused by botulinum toxin, a natural poison produced by the spore-forming bacteria Clostridium botulinum . Exposure to the botulinum toxin usually occurs from eating contaminated food although, in infants, it may be caused by specific types of clostridia obtained from soil or inhaled spores, causing growth of the bacteria in the infant's intestine. Botulinum toxin is a neurotoxin that blocks the ability of motor nerves to release acetylcholine, the neurotransmitter that relays nerve signals to muscles, a process that may result in unresponsive muscles, a condition known as flaccid paralysis. Breathing may be severely compromised in progressive botulism because of failure of the muscles that control the airway and breathing.
Botulism occurs only rarely, but its high fatality rate makes it a great concern for those in the general public and in the medical community. Clinical descriptions of botulism reach as far back in history as ancient Rome and Greece. However, the relationship between contaminated food and botulism was not defined until the late 1700s. In 1793 the German physician, Justinius Kerner (1786–1862), deduced that a substance in spoiled sausages, which he called wurstgift (German for sausage poison), caused botulism. The toxin's origin and identity remained vague until Emile van Ermengem (1851–1932), a Belgian professor, isolated Clostridium botulinum in 1895 and identified it as the source of food poisoning .
Three types of botulism have been identified: food-borne, wound, and infant botulism. The main difference between types hinges on the route of exposure to the toxin. Food-borne botulism accounts for 25 percent of all botulism cases and can usually be traced to eating contaminated home-preserved food. Infant botulism accounts for 72 percent of all cases. About 98 percent of infants recover with proper treatment. Although domestic food poisoning is a problem worldwide, concern is growing regarding the use of botulism toxin in biological warfare. At the end of the twentieth century 17 countries were known to be developing biological weapons, including the culture of botulism toxins.
Botulism is not spread from one individual to another, but through exposure to the deadly botulinum toxin, a natural poison produced by certain Clostridium bacteria that may be found in preserved, especially canned, foods and sometimes in the intestines of infants. Botulism spores can cause widespread illness if introduced into the environment.
Botulism occurs worldwide, with 90 percent of the comparatively rare cases occurring in the United States. Approximately 110 cases of botulism are reported annually in the United States, with 50 percent of cases in California alone. Infant botulism accounts for 72 percent of all cases, far exceeding both food-borne and wound botulism. Food-borne botulism accounts for 25 percent of all cases, primarily due to eating contaminated home-preserved food.
Causes and symptoms
Toxins produced by the bacterium Clostridium botulinum are the main culprit in botulism. Other members of the Clostridium genus can produce botulinum toxin, namely C. argentinense , C. butyricum , and C. baratii , but these are minor sources. To grow, these bacteria require a low-acid, oxygen-free environment that is warm (40–120°F or 4.4–48.8°C) and moist. Lacking these conditions, the bacteria transform themselves into spores that, like plant seeds, can remain dormant for years. Clostridia and their spores exist all over the world, especially in soil and aquatic sediments. They do not threaten human or animal health until the spores encounter an environment that favors growth. The spores then germinate, and the growing bacteria produce the deadly botulism toxin.
Scientists have discovered that clostridia can produce at least seven types of botulism toxin, identified as A, B, C, D, E, F, and G. Humans are usually affected by A, B, E, and very rarely F; infants are affected by types A and B. Domesticated animals such as dogs, cattle, and mink are affected by botulism C toxin, which also affects birds and has caused massive die-offs in domestic bird flocks and wild waterfowl. Botulism D toxin can cause illness in cattle, and horses succumb to botulism A, B, and C toxin. There have been no confirmed cases of human or animal botulism linked to the G toxin.
In humans, botulinum toxin latches onto specific proteins in nerve endings and irreversibly destroys them. These proteins control the release of acetylcholine, a neurotransmitter that stimulates muscle cells. With acetylcholine release blocked, nerves are not able to stimulate muscles. Ironically, this action of the botulinum toxin has given it a beneficial niche in the world of medicine. Certain medical disorders are characterized by involuntary and uncontrollable muscle contractions. Medical researchers have discovered that injecting a strictly controlled dose of botulinum toxin into affected muscles inhibits excessive muscle contractions. The muscle is partially paralyzed and normal movement is retained.
Human botulism (caused by botulism toxins A, B, and E) may stem from contaminated food, wound contamination, or the intestinal botulism toxin found in infants. Each produces multiple symptoms as follows:
- Food-borne botulism. Food that has been improperly preserved or stored can harbor botulinum toxin-producing clostridia. Canned or jarred baby food has also been known to cause botulism. Symptoms of food-borne botulism typically appear within 18 to 36 hours of eating contaminated food, with extremes of four hours to eight days. Initial symptoms include blurred or double vision and difficulty swallowing and speaking. Possible gastrointestinal problems include constipation , nausea , and vomiting . As botulism progresses, the victim experiences weakness or paralysis, starting with the head muscles and progressing down the body. Breathing becomes increasingly difficult. Without medical care, respiratory failure and death are very likely.
- Infant botulism. Infant botulism was first described in 1976. Unlike adults, infants younger than 12 months are vulnerable to C. botulinum colonizing the intestine. Infants ingest spores in honey or simply by swallowing spore-containing dust or dirt. The spores germinate in the large intestine and, once colonized, toxin is produced and absorbed into the infant's body from the entire intestinal tract. The first symptoms include constipation, lethargy, and poor feeding. As infant botulism progresses, sucking and swallowing (thus eating) become difficult. A nursing mother will often notice her own breast engorgement as the first sign of her infant's illness. The baby suffers overall weakness and cannot control head movements. Because of the flaccid paralysis of the muscles, the baby appears floppy. Breathing is impaired, and death from respiratory failure is a very real danger.
- Wound botulism. Confirmed cases of wound botulism have been linked to trauma such as severe crush injuries to the extremities, surgery, and illegal drug use. Wound botulism occurs when Clostridia colonize an infected wound and produce botulinum toxin. The symptoms usually appear four to 18 days after an injury occurs and are similar to food-borne botulism, although gastrointestinal symptoms may be absent.
When to call the doctor
Infant botulism may be hard for parents to identify because the symptoms occur slowly. Parents should call the doctor or take the infant or child to emergency services as soon as the child shows symptoms such as weakness or listlessness, lethargy, irritability, and poor eating (or nursing) along with decreased bowel movements or constipation. An affected child may be so weak as to appear floppy and not in control of muscle movements, especially movement of the neck and head. Whether parents are aware of a possible source of the botulism toxin, the suggestive symptoms should not be ignored.
Differential diagnosis of botulism can be complex because the symptoms mimic those of other diseases, especially diseases characterized by muscle weakness. Botulism must be differentiated from diseases such as the following:
- Guillain-Barré syndrome
- myasthenia gravis
- systemic poisoning or sepsis
- reactions to therapeutic drugs
- nervous system infection
- carbon monoxide or atropine intoxication
- severe allergic reactions to bee sting, shell fish, and other allergens
- failure to thrive
Sepsis is the most common initial diagnosis for actual infant botulism, and meningoencephalitis may also be the diagnosis if irritability and lethargy are present. Infant botulism was at one time linked to 5 to 15 percent of cases of sudden infant death syndrome (SIDS, crib death) because of spores found in 4 to 15 percent of cases; however, a subsequent 10-year study did not find a significant influence of botulism on SIDS.
Laboratory tests are used to make a definitive diagnosis, but if botulism seems likely, treatment starts immediately without waiting for test results, which may take up to two days. Diagnostic tests focus on identifying the organism causing the illness. This may involve performing a culture on contaminated material from the suspect food or the nose or throat of the affected individual. In infant botulism, the infant's stool may be cultured to isolate the organism; this test may be performed by the state health department or the Centers for Disease Control (CDC). Culture results are available from the microbiology laboratory as soon as bacteria grow in a special plate incubated at temperatures at or above body temperature. The growth of Clostridium confirms the diagnosis. Sometimes the organism cultured is not Clostridium as suspected. The microbiology laboratory may use samples of the bacteria grown to perform other special techniques in order to help identify the causative organism.
While waiting for diagnostic test results, doctors ask about recently consumed food, possible open sores, recent activities and behavior, and other factors that may help to rule out other disease possibilities. A physical examination is done with an emphasis on the nervous system and muscle function. As part of this examination, imaging studies such as CT and MRI may be done and electrodiagnostic muscle function tests (electromyogram) or lumbar punctures may be ordered. Laboratory tests look for the presence of botulinum toxin or Clostridia in suspected foods and/or the child's blood serum, feces, or other specimens for traces of botulinum toxin or Clostridia . Magnesium levels may be measured, since magnesium increases the activity of Clostridium . Additional diagnostic tests may be done to rule out other diseases or conditions with similar symptoms.
Older children and adults with botulism are sometimes treated with an antitoxin derived from horse serum that is distributed by the Centers for Disease Control and Prevention. The antitoxin (effective against toxin types A, B, and E) inactivates only the botulinum toxin that is unattached to nerve endings. Early injection of the antitoxin, ideally within 24 hours of onset of symptoms, can preserve nerve endings, prevent progression of the disease, and reduce mortality.
Unfortunately, infants cannot receive the antitoxin used for adults. For them, human botulism immune globulin (BIG) is the preferred treatment. It is available in the United States through the Infant Botulism Treatment and Prevention Program in Berkeley, California. BIG neutralizes toxin types A, B, C, D, and E before they can bind to nerves. This antitoxin can provide protection against A and B toxins for approximately four months. Though many infants recover with supportive care, BIG cuts hospital stay in half and, therefore, reduces hospital costs by 50 percent as well.
Aside from the specific antitoxin, no therapeutic drugs are used to treat botulism. Antibiotics are not effective for preventing or treating botulism because the Clostridium group of toxins are not sensitive to them. In fact, antibiotic use is discouraged for infants because bacteria could potentially release more toxin into a baby's system as they are killed. Antibiotics can be used, however, to treat secondary respiratory tract and other infections.
Treatment for infants usually requires them to be in an intensive care unit, involving intensive respiratory support and nasogastric tube feeding for weeks or even months. Once an infant can breathe unaided, physical therapy is initiated to help the child relearn how to suck and swallow. In older children and adults, a respirator is often required to assist breathing; a tracheostomy may be necessary in some cases.
Surgery may be necessary to clean an infected wound (debridement) and remove the source of the bacteria producing the toxin. Antimicrobial therapy may be necessary.
When botulism in older children or adults is caused by food, it often is necessary to flush the gastrointestinal tract (gastric lavage). Often cathartic agents or enemas are used. It is important to avoid products that contain magnesium, since magnesium enhances the effect of the toxin.
Parents should avoid feeding honey to infants younger than 12 months because it is one known source of botulism spores.
With medical intervention, botulism victims can recover completely, though it may be a very slow recovery. It takes weeks to months to recover from botulism, and
Vaccines have not been developed directed against botulism, which makes prevention of infant botulism or other forms of the disease difficult, since exposure to the botulinum toxic is typically unrecognized. Food safety is the surest prevention for botulism. Botulinum toxin cannot be seen, smelled, or tasted, so the wisest course is to discard any food that seems spoiled; avoid eating food from dented, rusty, or bulging cans; avoid refreezing meats once they have been thawed; and avoid buying broken containers of food or eating food that has been stored at room temperature or above for more than a few hours. People who like to can food at home must be diligent about using sterile equipment and following U.S. Department of Agriculture canning guidelines.
Infant botulism is difficult to prevent, because controlling what goes into an infant's mouth is often beyond control, especially in regard to airborne spores. One concrete preventative is to never feed honey to infants younger than 12 months as it is one known source of botulism spores. As infants begin eating solid foods, the same food precautions should be followed as for older children and adults.
Because symptoms of infant botulism appear slowly, parents may be concerned that they will be missed or not found early. Normal watchfulness of the parents is sufficient, paying attention to any change in feeding, a decrease in bowel movements, or a lack of normal responses such as turning of the head and body movements. It may be helpful to remember how rare botulism is, how easy it is to assure food safety, and also that morbidity and mortality can be avoided with early recognition of the symptoms.
Acetylcholine —A chemical called a neurotransmitter that functions primarily to mediate activity of the nervous system and skeletal muscles.
Antitoxin —An antibody against an exotoxin, usually derived from horse serum.
Computed tomography (CT) —An imaging technique in which cross-sectional x rays of the body are compiled to create a three-dimensional image of the body's internal structures; also called computed axial tomography.
Culture —A test in which a sample of body fluid is placed on materials specially formulated to grow microorganisms. A culture is used to learn what type of bacterium is causing infection.
Electrooculography (EOG) —A diagnostic test that records the electrical activity of the muscles that control eye movement.
Flaccid paralysis —Paralysis characterized by limp, unresponsive muscles.
Lumbar puncture —A procedure in which the doctor inserts a small needle into the spinal cavity in the lower back to withdraw spinal fluid for testing. Also known as a spinal tap.
Magnetic resonance imaging (MRI) —An imaging technique that uses a large circular magnet and radio waves to generate signals from atoms in the body. These signals are used to construct detailed images of internal body structures and organs, including the brain.
Neurotoxin —A poison that acts directly on the central nervous system.
Neurotransmitter —A chemical messenger that transmits an impulse from one nerve cell to the next.
Sepsis —A severe systemic infection in which bacteria have entered the bloodstream or body tissues.
Spore —A dormant form assumed by some bacteria, such as anthrax, that enable the bacterium to survive high temperatures, dryness, and lack of nourishment for long periods of time. Under proper conditions, the spore may revert to the actively multiplying form of the bacteria. Also refers to the small, thick-walled reproductive structure of a fungus.
Toxin —A poisonous substance usually produced by a microorganism or plant.
Tracheostomy —A procedure in which a small opening is made in the neck and into the trachea or windpipe. A breathing tube is then placed through this opening.
Rosaler, Maxine. Botulism. New York: Rosen Publishing Group, 2004.
Cadou, Stephanie G. "Diagnosing Infant Botulism." The Nurse Practitioner 26, no. 3 (March 2001): 76.
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. Web site: http://www.cdc.gov.
L. Lee Culvert Janie F. Franz