Botulism

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Botulism

Introduction

Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

BIBLIOGRAPHY

Introduction

Botulism is a disease that is caused by a bacterial toxin. The toxin is one of seven (A-G) made and released by the bacterium Clostridium botulinum. Botulism toxin types A, B, E, and F cause botulism in humans. Another bacterium called Clostridium baratii can also produce a disease-causing toxin, but this bacterium is rarely encountered, and is responsible for far fewer cases of botulism than is C. botulinum.

Botulism toxins are powerful neurotoxins; they affect nerves and can produce paralysis. One microgram of toxin—a millionth of a gram—can kill a person. Paralysis from botulism affects the functioning of organs and tissues, and when botulism is fatal, it is usually due to failure of the respiratory muscles.

Disease History, Characteristics, and Transmission

Botulism was first described in 1735 in an illness outbreak that was traced to the consumption of contaminated German sausage. Indeed, the word botulism was derived from the Latin word botulus, meaning sausage.

C. botulinum are commonly found in soil. They can be present on vegetables and other food grown in soil, and can be eaten if the food is not completely washed free of bacteria. Fortunately, under these conditions where oxygen is present, the bacteria do not produce the toxin and so are harmless when eaten. Botulism is not a contagious disease—it cannot be spread from person to person. Rarely, botulism occurs as the result of a wound infected with C. botulinum.

The toxin is produced when the bacterium grows in the absence of oxygen. Growth of the bacteria in, for example, the low-oxygen and slightly acidic environment (the bacteria cannot grow above pH 5) of some canned foods is associated with the production of gas. Canned foods can bulge due to the build-up of the gas. Discarding a bulging unopened can is always a wise precaution. With foodborne botulism, growth of the bacteria in the food may occur, but is not mandatory for developing botulism, as the presence of the toxin alone is sufficient to cause illness. Because the toxin causes the illness, foodborne botulism is often described as a food intoxication.

Rarely, botulism can also be caused by the infection of C. botulinum in an open wound. Growth of the bacteria deep in the tissues leads to the production of the toxin, which then spreads via the bloodstream.

Symptoms of botulism are produced when the toxin enters the bloodstream. The toxin blocks the production of a neurotransmitter called acetylcholine, a chemical that bridges the physical gap between nerve cells and so aids in the transmission of impulses from nerve to nerve. As nerves are affected and paralysis occurs, a person experiences difficulty seeing, talking, and swallowing, and can become nauseous.

C. botulinum is one of a few types of bacteria that can produce a structure known as a spore. A spore is a form of the bacterium that is non-growing but which can persist in that form for a long time and in conditions of excess heat, dryness, and other harsh environments that would kill the normally growing cell. The spore form allows the organism to survive inhospitable conditions and then, when conditions improve, such as in canned food or inside the body, the bacteria can resume growth, division, and toxin production.

WORDS TO KNOW

NEUROTOXIN: A poison that interferes with nerve function, usually by affecting the flow of ions through the cell membrane.

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.

Scope and Distribution

Botulism is a fairly rare illness. In the United States, for example, only about 100 cases have been reported each year since the 1990s. Most cases are due to the improper canning of foods at home.

The different forms of the botulism toxin display some differences in their geography. In the United States, type A botulism, which is the most severe, occurs most often in western regions, particularly in the Rocky Mountains. Type B toxin, whose symptoms tend to be less severe, is more common in the eastern United States. Type E toxin is found more in the bacteria that live in fresh water sediments. The reasons for their different distributions is not clear.

Treatment and Prevention

Diagnosis of botulism is complicated by the fact that the disease is infrequently seen. A physician may have little experience in dealing with the illness. As well, in its early stages, botulism has symptoms that are similar to other ailments such as Guillain-Barré syndrome and stroke. Both of these considerations sometimes lead to a delayed diagnosis of botulism.

Diagnosis involves the detection of toxin in the infected person's blood, which can be accomplished using specific immune components, or antibodies. An antibody to the specific botulism toxin will react with the toxin, producing a visible clump of material. As well, sometimes living bacteria can be recovered from the feces.

Treatment for botulism often involves the administration of an antibody-containing antitoxin that blocks the binding of the toxin to the nerve cells. With time, paralysis fades. However, recovery can take many weeks. If botulism is suspected soon after exposure to the bacteria, the stomach contents can be emptied to remove potentially contaminated undigested food. When lung muscles have been affected, a patient may need mechanical assistance in breathing.

Impacts and Issues

A century ago, botulism was frequently a death sentence— one of every two people who became ill with it died. In 2007, of the approximately 100 people predicted to become ill with botulism in the United States, eight will die. In contrast to some other diseases that take a toll on the underdeveloped of the world, botulism is more prevalent in developed regions, particularly where food is processed, canned, and sold.

Botulism does have significance in its potential as a bioterrorist threat. This potent killing power of the Clostridium neurotoxins has been recognized for decades. During World War II (1939–1945), several nations including the United States and Canada experimented with the development of botulism toxin-based weapons. Sprays that contained the spore form of C. botulinum were developed and tested. The idea was that inhalation of the spores would lead to resumed growth of the bacteria and production of the lethal neurotoxin. The sprays were never used in battle.

Botulinum toxin A is exploited cosmetically as a means of lessening wrinkles. Injection of Botox relaxes muscles, which can produce a more youthful appearance. The American Society of Aesthetic and Plastic Surgery (ASAPS) estimates that the worldwide market for Botox is around 900 million dollars annually, and over two million Botox procedures are performed per year. Botulinum toxin A has also shown promise in lessening dystonia (muscle spasms) that occurs in cerebral palsy, and in treating crossed eyes (strabismus).

In 1976, a form of botulism was recognized in infants in the United States that stemmed from babies ingesting C. botulinum spores, which colonized their intestinal tract (an infant's intestinal tract is less acidic than that of an adult) and eventually produced botulinum toxin. Evidence indicated that honey was linked with both the reservoir of the bacteria and the resulting disease. Since that time, honey-linked infant botulism has been reported in other countries, prompting recommendations from the American Academy of Pediatrics for all infants less than 12 months of age not to receive foods containing honey.

As botulism is a rare occurrence, The Centers for Disease Control and Prevention (CDC) maintains a central supply of antitoxin against botulism. State health departments consult with the CDC for release of the antitoxin when a case has been reported to them. Fast action is essential, as the antitoxin reduces the severity of the symptoms only if given early.

When a food source of botulism is discovered, the Food and Drug Administration (FDA) issues a class-1 recall of the product. Class-1 recalls are reserved for dangerous or defective products that could cause serious health problems or death, and involve communication between the FDA, manufacturer or supplier, and the public to remove the product from the market, or remove the food source from the food supply. For instance, in February 2007, the FDA issued a warning against consumption of Earth's Best Organic 2 Apple Peach Barley Breakfast baby food because of the risk of contamination with Clostridium botulinum. The manufacturer initiated a recall of the food, and working in conjunction with the FDA, removed the potentially contaminated baby food jars from store shelves, began an awareness campaign, and tracked and corrected the source of the contamination. As of March 2007, a potential outbreak of infant botulism was prevented, and no cases of infant botulism were reported from ingesting Earth's Best Organic baby food.

IN CONTEXT: BOTULINUM TOXIN AS A BIOLOGICAL WEAPON

According to the CDC, aerosolized botulinum toxin is a possible mechanism for a bioterrorism attack. As yet inhalational botulism cannot, however, be clinically differentiated from the naturally occurring forms. What factors might assist or complicate the definitive initial determination of such an attack?

Key clinical or epidemiological factors assisting the determination of an intentional attack:

Inhalational botulism does not occur naturally.
Botulism is not transmissible from person-to-person.
Indications of intentional release of a biologic agent aerosolized botulinum toxin might include an unusual geographic clustering of illness (e.g., persons who attended the same public event or gathering).
Symptoms begin within six hours to two weeks after exposure (often within 12 to 36 hours).

SOURCE: Centers for Disease Control and Prevention (CDC)