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Botulism is a disease caused by the toxins (poisons) produced by several
members of the group of bacteria called Clostridium botulinum. These
bacteria are found in soil throughout the world and produce spores that are able
to survive in a dormant state until more favorable conditions allow them to
grow.
The seven distinct toxins they produce are some of the most deadly
substances known. The toxins are designated by the letters A through G, and
types A, B, E and F toxins have produced human disease. Botulinum toxins affect
people of all ages by preventing certain nerves from functioning, resulting in
muscle paralysis. Because of this action, these toxins are designated
"neurotoxins."
Botulism in humans is most often the result of eating food
containing the toxin. Botulinum neurotoxins also are a serious bioterrorism
concern because the toxins are relatively easy to make and deliver and are
highly lethal. Unlike infectious diseases, however, botulism cannot be
transmitted from one person to
another.
Transmission
Food-borne botulism is caused by
eating foods contaminated with botulinum spores that grow into bacteria and
produce neurotoxin in the food. A common cause of this illness is improperly
preserved home-processed foods with low-acid content, such as green beans, beets
and corn. Less likely sources include fish products and other commercially
processed foods. The actual number of cases in the United States is small with
approximately nine outbreaks of food-borne botulism per year with an average of
2.4 cases per outbreak.
Wound botulism occurs when C. botulinum
spores contaminate a wound, germinate, grow within the wound and produce toxin
that is absorbed into the bloodstream. Wound botulism is associated with crush
injuries and with illicit drug use. The increasing number of people who inject
black tar heroin from Mexico is a growing concern because this crude drug can
contain C. botulinum spores.
Infant botulism occurs when an infant
consumes the spores of C. botulinum, which then grow in the baby's
intestines and produce toxins. A number of such cases have been associated with
eating honey contaminated with C. botulinum spores.
Botulinum
toxins, however, do have beneficial uses. Doctors use it to treat certain human
diseases caused by muscle problems, such as strabismus (crossed eyes). It also
is used to eliminate facial wrinkles.
Symptoms
Symptoms
produced by each toxin type are quite similar. The first symptoms of botulism
may include:
· Double vision
· Blurred vision
· Drooping eyelids
· Slurred speech
· Difficulty swallowing
· Muscle weakness
If a health care provider cannot identify and treat the disease early, the
symptoms progress to paralysis of the arms, legs, trunk and respiratory system.
People with respiratory symptoms may have to use a ventilator to help them
breathe until they recover from the toxin, which normally requires two to eight
weeks. Death occurs in 5 percent to 10 percent of cases of food-borne
botulism.
Diagnosis
Because botulism occurs rarely and the
symptoms are similar to other neurological diseases, diagnosis is difficult and
the disease is frequently misdiagnosed. The laboratory test used to confirm a
diagnosis of botulism is sensitive and specific but can take up to four days to
complete and is available in only a few
laboratories.
Treatment
Treatment of botulism includes
careful observation, supportive care and administering the antitoxin. The
antitoxin will reduce the progression of the paralysis and may reduce the
severity and duration of symptoms. Patients may still require weeks to months of
supportive care, however, before they fully recover.
Antibiotics are of
little use to treat the symptoms caused by the toxin, but health care providers
use them to treat wound botulism.
Currently, there is no vaccine approved
by the U.S. Food and Drug Administration for botulism. Research on a vaccine,
however, is at an advanced stage. People who work with the toxin (such as
laboratory workers) and who are at high risk of exposure can be immunized with
botulinum toxoid (a drug that researchers are investigating).
Botulism
as an Agent of Bioterrorism
Botulinum toxin has been a concern as a
potential biological warfare agent since World War II. In response to concerns
about Germany's botulinum toxin research, the United States and Great Britain
developed countermeasures against the toxin before the invasion of Europe. More
recently, Iraq has been accused of producing large amounts of botulinum toxin
for use as a biological warfare agent. The extreme toxicity of botulinum toxins
and the ease of production, transport and delivery make this an agent of extreme
bioterrorism concern.