Botulism is caused by a group of paralytic neurotoxins produced by the spore-forming anaerobic gram-positive bacillus Clostridium botulinum. Intoxication can occur naturally from contaminated foods or rarely as a result of wound or intestinal colonization in humans. There are 7 types of botulinum toxins, A through G, although only A, B, E, and F have been implicated in the poisoning of humans.
Botulism is classified as a Category A bioterrorism agent because of its ease of dissemination and high mortality rate. When used as a biological weapon, botulinum toxin is most likely to be dispersed as an aerosol for inhalation, although it could be added to the food or water supply. Botulinum toxins are, by weight, the most toxic agents known, with an LD50* of only 0.001 mcg/kg.
Botulinum toxin irreversibly binds to the pre-synaptic cholinergic neuromuscular junction, blocking acetylcholine release and manifesting as a symmetric progressive descending flaccid paralysis with bulbar palsies after an 18- to 72-hour incubation period. Multiple cranial nerve palsies are evident early in the course of the disease. Symptom severity ranges from mild to frank paralysis.
Patients are afebrile with initial complaints of blurred vision, diplopia, and mydriasis with photophobia, ptosis, ophthalmoplegia, hoarseness, dysarthric speech, and dysphagia. Constipation, dry mouth, and urinary retention may also occur. Patients remain awake, alert, and oriented throughout the entire illness. Symptoms progress in a descending pattern to produce a skeletal muscle paralysis that may cause sudden respiratory arrest and death if untreated. Severe poisonings may require months of ventilatory support.
Following an aerosol release, the toxin may be swallowed as well as inhaled. In food-acquired cases, nausea, vomiting, and diarrhea may precede the paralysis, and cases will cluster around consumption of the contaminated food at a restaurant or from improper home canning.
Botulism has a mortality rate of 5%-10% (up to 30% in victims over 60 years of age). Botulism is not spread person to person. Botulinum toxins are odorless and colorless in solution. Five minutes of heating the toxin above 85°C (185°F) will inactivate the toxin. An antitoxin is available from the CDC.
People at higher risk for contracting food-borne botulism are nursing home residents, dormitory residents, wedding guests, and large event attendees. Intestinal botulism occurs in infants, and IV drug users are likely candidates for wound botulism. Food-borne botulism is a public health emergency and must be reported to state or local health departments as well as the CDC.
Note: To prevent aerosol inhalation, use a HEPA or N-95 filter mask (lacking this, a surgical mask may provide some protection). Minute quantities of C. botulinum acquired by ingestion, inhalation, or absorption can cause death.
All materials suspected of containing toxin must be handled with caution. Prior to the shipment of any botulism-associated specimen, the designated laboratory must be notified and approved by the state health department.
*LD50 (LD = lethal dose) is the amount of a material, given all at once, that causes death in 50% of its recipients.