Botulism

Botulism, an acute neurologic disease resulting from intoxication with Clostridium botulinum, occurs sporadically and in focal outbreaks throughout the world, related to wound contamination by the bacterium or ingestion of food-borne toxin (Bleck, 2005). Aerosol forms of the toxin, while a rare mode of acquisition in nature, have been weaponized for use in bioterrorism (Zilinskas, 1997). Botulinum toxin is considered to be the most toxic molecule known; it is lethal to humans in minute quantities. It acts by blocking the release of the neurotransmit-ter acetylcholine from presynaptic vesicles, thereby inhibiting muscle contraction (Arnon et al., 2001). Botulism therefore possesses a number of attributes of concern: it is lethal in small quantities; it has been successfully weaponized in the past; and its deployment by terrorists could paralyze a health-care system.

Botulism presents clinically as an acute, afebrile, symmetric, descending, flaccid paralysis. The disease manifests initially in the bulbar musculature, and is unassociated with mental status or sensory changes. Fatigue, dizziness, dysphagia, dysarthria, diplopia, dry mouth, dyspnea, ptosis, ophthalmoparesis, tongue weakness, and facial muscle paresis are early findings seen in more than 75 percent of cases (Arnon et al., 2001). Progressive muscular involvement leading to respiratory failure may ensue. The clinical presentations of food-borne and inhalational botulism are indistinguishable in experimental animals (Arnon et al., 2001).

The diagnosis of botulism is largely based on epidemiologic and clinical features and the exclusion of other possibilities (see Table 12.5). Clinicians should recognize that any single case of botulism could be the result of sporadic food-borne exposure, the sentinel case of a larger-scale "natural" outbreak, or a bioterrorism attack. A large number of epidemiologically unrelated, multifocal cases should be clues to an intentional release of the agent, either in food or water supplies or as an aerosol.

The mortality from food-borne botulism has declined from 60 percent to 6 percent over the last four decades, representing progress in supportive care and mechanical ventilation more than specific therapies (Arnon et al., 2001). The prolonged need for ventilatory support would rapidly deplete the availability of limited resources, such as ventilators, in the event of a large-scale bioterrorism event involving botulism. Treatment with an equine antitoxin may ameliorate disease if given early, but this is available only in very limited supply from the CDC.

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