Botulism is a disease caused by a
bacterial toxin produced by Clostridium botulinum (Figure
5). There are 7
different types of botulinum toxin: A, B, C, D, E, F, and G. The bacterium is found all
over the world and is commonly isolated from water and soil. Most cases of
botulism are associated with food consumption. The most common types of
toxin seen in foodborne disease are A, B, and E. The
toxin inhibits proper functioning of the nerves and prevents muscle contraction. As a result a person with
severe botulism will have flaccid paralysis and may not be able to breathe
(Figure 6). The death rate of botulism during the 1990’s was 6% (9,
47).
This bacterium exists in two forms: vegetative cells and spores. The vegetative cells of Clostridium botulinum are killed by oxygen. The spores allow the organism to survive when nutrients are low and/or oxygen levels are too high. The vegetative cells produce the toxin. This toxin is very potent. Only minute amounts are needed to cause severe disease (LD50= 1 ng/kg). Usually the toxin is ingested which results in symptoms of botulism 24-36 hours later.
Clostridium botulinum spores
are highly resistant to killing by heat. Temperatures of 121o C (250o
F) or higher are needed to kill the spore. If a canned food is improperly
prepared the surviving spores germinate producing vegetative cells. The
vegetative cells can grow in the low oxygen environment inside the can and
produce toxin. Once toxin is made the food must be cooked for at
least 5 minutes at 85o C (185o F; 60)
to destroy it.
The initial signs of botulism include
blurred vision with fixed and dilated pupils, dry mouth,
constipation and abdominal pain; fever is absent. Many patients will complain of
difficulty seeing, speaking and swallowing. Other symptoms
of botulism include double vision, drooping eyelids, slurred speech, difficulty
swallowing, muscle weakness that descends starting at the head: the
shoulders are then affected, followed by the upper arms, and then the lower arms, thighs,
calves, and so forth. Paralysis of breathing muscles can cause a person to stop
breathing and die, unless mechanical ventilation is
provided. The most common cause
of death is respiratory failure. If mechanical ventilation is not given the death
rate can be as high as 70%. It can take several weeks before a person with
severe botulism can breathe without mechanical ventilation. Complete recovery of
all the nerves can take many months to years. Botulism,
similar to, anthrax is not spread from person-to-person.
There are three kinds of
botulism:
Foodborne botulism
occurs when people ingest pre-formed toxin in improperly
canned or fermented food. If the food is improperly processed then spores of Clostridium
botulinum present on the food survive and will become vegetative
cells. The vegetative cells produce the toxin. This toxin is the most poisonous
substance known to man. The
lethal dose of botulinum toxin for humans is not known but can be
estimated from studies with primates. It is estimated that lethal
amounts of crystalline type A toxin for a 155-lb (70-kg) human would
be about 70 mg (47).
Symptoms begin within 6 hours to 2 weeks (most commonly between 12 and 36 hours)
after eating toxin-containing food. Foodborne botulism is a public health
emergency because the contaminated food may still be available for ingestion by
others. Around 23 cases of foodborne botulism have occurred per year from 1990
to 2000 (60).
Infant botulism, the most common form of botulism, occurs in around 100 infants each year (9). Usually infants under 1 year of age consume the spores of the botulinum bacteria, which then germinate and become vegetative cells in the intestines and release toxin. Most cases of infant botulism result from ingestion of spores present in the soil and dust. In most cases the source of the spores is not known. The most common foodstuff associated with infant botulism is honey.
Once infants ingest Clostridium botulinum spores the spores
escape being killed in the stomach due to the fact that they produce lower levels of
acid in their stomach. The
intestines of the infants also lack the proper number of normal bacterial flora
to prevent the growth of the vegetative Clostridium botulinum cells.
Symptoms include constipation, and a weakness in sucking, swallowing, or crying,
general muscle weakness followed by progressive weakness of the muscles in the
mouth and throat as well as weakness of the limbs (figure
6). These infants do
not eat well or gain weight at a normal rate. Flaccid paralysis can can occur but is less common
than in foodborne botulism only affecting 1-2%
of infants.
Wound botulism,
the least common (around 4 cases/year) occurs when wounds are contaminated with Clostridium
botulinum spores. The spores germinate in the wound and then produce the
toxin. The incubation time is longer than with the other
forms of this disease: 4 days or longer. Symptoms associated with the
gastrointestinal tract are less common (dry mouth, abdominal pain).
Injection drug users (IV drug abusers) are at higher risk for this form of botulism.
Why is botulinum toxin an
attractive BW?
The botulism toxin can be used
in an aerosol attack and may result in many causalities. If
the toxin is inhaled symptoms might not appear for several days (61). Fortunately,
botulism cannot spread to others who have close contact with them. One gram of
this toxin if dispersed and inhaled evenly could kill 1 million people. If
released as an aerosol it could incapacitate or kill 10% of the people within
500 meters downwind of the BW release. There are seven different types of the
toxin. Antibodies used to treat botulism are only useful in treating people that
have toxins A, B and E in their systems. If botulinum toxin to any of the other
4 toxins were released antitoxin therapy would not be helpful. Treatment of this disease is labor
intensive, may require expensive equipment and takes weeks to months before the
persons completely recover.
Laboratory
Diagnosis
Physicians may consider the diagnosis if the patient's history and physical
examination suggest botulism. However, a number of other diseases have similar
symptoms. Diseases such as Guillain-Barré syndrome, stroke, and myasthenia
gravis have to be excluded to confirm a diagnosis of botulism. Other tests
that can help in diagnosis include brain scans, spinal fluid examination, nerve conduction
tests (electromyography, or EMG), and a tensilon test (myasthenia gravis).
The most direct way to confirm the diagnosis of botulism is to demonstrate
the botulinum toxin in the patient's serum or stool by injecting serum or stool
into mice and looking for signs of botulism. The bacteria can also be isolated
from the stool of persons with foodborne and infant botulism. These tests can be
performed at some state health department laboratories and at the Centers for
Disease Control in Atlanta, Georgia.
Treatment
The following treatments are required
for someone with botulism.
Most patients eventually recover after
weeks to months of supportive care.
Prevention
Do not give infants under the age of one food known to contain Clostridium
botulinum spores (honey). Certain conditions stop growth of Clostridium
botulinum; temperatures below 4oC, acid pH (acidic foods like
tomato sauces), heating the food before consumption (85oC or 185oF
for 5 minutes). Home canning of food is more likely to result in botulism so the
safest canned foods would be those purchased from commercial sources. If you still
wish to can foods at home follow the manufacturers instructions exactly when
canning foodstuffs.
A vaccine is currently being developed and could in the near future be available. However, it is likely that at first it will only be available for military personnel.
© 2005 Neal Chamberlain. All rights reserved.
Site Last Revised 5/5/05
Neal Chamberlain, PhD. A. T. Still University of Health Sciences/Kirksville
College of Osteopathic Medicine.
Site maintained by: Neal R. Chamberlain PhD.: nchamberlain@atsu.edu