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Botulism
Botulism (Latin, botulus, "sausage") is a rare but serious paralytic illness caused by botulin toxin. The toxin is produced by the bacteria Clostridium botulinum. C. botulinum is an anaerobic, Gram positive, spore-forming rod. Botulin toxin is one of the most powerful known toxins: about one microgram is lethal to humans. It acts by blocking nerve function and leads to respiratory and musculoskeletal paralysis.
There are three main kinds of botulism:
All forms of botulism can be lethal and are always considered medical emergencies. Foodborne botulism can be extremely dangerous as a public health risk because multiple persons can consume the poison from a single contaminated food source.
Prevalence
An average of 110 cases of botulism are reported each year in the United States. Of these, approximately, 72% are infant botulism, and 3% are wound botulism. Outbreaks of foodborne botulism involving two or more persons occur during most years and are usually caused by the consumption of home-canned foods. The number of cases of foodborne and infant botulism has changed little in recent years, but wound botulism has increased because of the use of black tar heroin, especially in California.[1] In July 2007, a widespread recall was initiated due to botulism contamination of food manufactured by Castleberry's Food Company.[2] Shortly thereafter, in August 2007, the FDA issued a warning of botulism risk from canned French cut green beans manufactured by Lakeside Foods Inc, of Manitowoc, Wisconsin.[3]
Symptoms
Food-borne and wound botulism
Normal symptoms usually include dry mouth, double and/or blurred vision, difficulty swallowing, muscle weakness, drooping eyelids, difficult breathing, slurred speech, vomiting, urinary incontinence and sometimes diarrhea. These symptoms may continue to cause paralytic ileus with severe constipation, and will lead to body paralysis. The respiratory muscles are affected as well, which may cause death due to respiratory failure. These are all symptoms of the muscle paralysis caused by the bacterial toxin.
In all cases illness is caused by the toxin made by C. botulinum, not by the bacterium itself. The pattern of damage occurs because the toxin affects nerves that are firing more often.[4]
Treatment
The respiratory failure and paralysis that occur with severe botulism may require a patient to be on a breathing machine for weeks, plus intensive medical and nursing care. After several weeks, the paralysis slowly improves. If diagnosed early, foodborne and wound botulism can be treated by inducing passive immunity with a horse-derived antitoxin, which blocks the action of toxin circulating in the blood.[5] This can prevent patients from worsening, but recovery still takes many weeks. Physicians may try to remove contaminated food still in the gut by inducing vomiting or by using enemas. Wounds should be treated, usually surgically, to remove the source of the toxin-producing bacteria. Good supportive care in a hospital is the mainstay of therapy for all forms of botulism.
Besides supportive care, infant botulism can be treated with human botulism immune globulin (BabyBIG), when available. Supply is extremely limited, but is available through the California Department of Health Services. This dramatically decreases the length of illness for most infants. Paradoxically, antibiotics (especially aminoglycosides or clindamycin) may cause dramatic acceleration of paralysis as the affected bacteria release toxin. Visual stimulation should be performed during the time the infant is paralyzed as well, in order to promote the normal development of visual pathways in the brain during this critical developmental period.
Furthermore each case of food-borne botulism is a potential public health emergency in that it is necessary to identify the source of the outbreak and ensure that all persons who have been exposed to the toxin have been identified, and that no contaminated food remains.
There are two primary Botulinum Antitoxins available for treatment of wound and foodborne botulism. Trivalent (A,B,E) Botulinum Antitoxin is derived from equine sources utilizing whole antibodies (Fab & Fc portions). This antitoxin is available from the local health department via the CDC. The second antitoxin is heptavalent (A,B,C,D,E,F,G) Botulinum Antitoxin which is derived from "despeciated" equine IgG antibodies which have had the Fc portion cleaved off leaving the F(ab')2 portions. This is a less immunogenic antitoxin that is effective against all known strains of botulism where not contraindicated. This is available from the US Army. On 1 June 2006 the US Department of Health and Human Services awarded a $363 million contract with Cangene Corporation for 200,000 doses of Heptavalent Botulinum Antitoxin over five years for delivery into the Strategic National Stockpile beginning in 2007.[6]
Complications
Botulism can result in death due to respiratory failure. However, in the past 50 years, the proportion of patients with botulism who die has fallen from about 50% to 8% due to improved supportive care. A patient with severe botulism may require a breathing machine as well as intensive medical and nursing care for several months. Patients who survive an episode of botulism poisoning may have fatigue and shortness of breath for years and long-term therapy may be needed to aid their recovery.
Infant botulism has no long-term side effects, but can be complicated by nosocomial adverse events. The case fatality rate is less than 1% for hospitalized infants with botulism.
Diagnosis
Physicians may consider the diagnosis if the patient's history and physical examination suggest botulism. However, these clues are often not enough to allow a diagnosis of botulism. Other diseases such as Guillain-Barré syndrome, stroke, and myasthenia gravis can appear similar to botulism, and special tests may be needed to exclude these other conditions. These tests may include a brain scan, cerebrospinal fluid examination, nerve conduction test (electromyography, or EMG), and an Edrophonium Chloride (Tensilon) test for myasthenia gravis. A definite diagnosis can be made if botulinum toxin is identified in the feed, stomach or intestinal contents, vomit or faeces. The toxin is occasionally found in the blood in peracute cases. Botulinum toxin can be detected by a variety of techniques, including enzyme-linked immunosorbent assays (ELISAs), electrochemiluminescent (ECL) tests and mouse inoculation or feeding trials. The toxins can be typed with neutralization tests in mice. In toxicoinfectious botulism, the organism can be cultured from tissues. On egg yolk medium, toxin-producing colonies usually display surface iridescence that extends beyond the colony.[9]
In cattle, the symptoms may include drooling, restlessness, inco-ordination, urine retention, dysphagia, and sternal recumbency. Laterally recumbent animals are usually very close to death. In sheep, the symptoms may include drooling, a serious nasal discharge, stiffness, and inco-ordination. Abdominal respiration may be observed and the tail may switch on the side. As the disease progresses, the limbs may become paralysed and death may occur.
The clinical signs in horses are similar to cattle. The muscle paralysis is progressive; it usually begins at the hindquarters and gradually moves to the front limbs, neck, and head. Death generally occurs 24 to 72 hours after initial symptoms and results from respiratory paralysis. Some foals are found dead without other clinical signs.
Pigs are relatively resistant to botulism. Reported symptoms include anorexia, refusal to drink, vomiting, pupillary dilation, and muscle paralysis.[10]
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