To date, seven immunologically distinct forms of botulinum toxins, labeled A through G, have been identified. Botulism in humans has generally been associated with A, B, E, or F toxins, whereas the C and D toxins have been identified in botulism outbreaks among various animal species, as shown in Table VIII.19.1.

Clinical Manifestation and Pathology

The onset of disease usually occurs within 12 to 36 hours of ingestion of food contaminated with botulinum toxin. Botulism typically presents with an array of distressing signs of motor nerve dysfunction, including double or blurred vision and difficulty with speech and swallowing. The unabated disease progresses to generalized paralysis and death from respiratory muscle involvement.

Diagnosis is confirmed by detecting botulinum toxin in the blood, feces, or wound site of the patient. Depending on the dose of toxin, untreated botulism carries a high fatality rate. Early treatment with antitoxin accompanied by respiratory assistance and other supportive intensive care may be life-saving.

The pathophysiology involves inhibition of release of the neurotransmitter substance acetylcholine at the neuromuscular junction, thus preventing the initiation of the electrical impulse needed for muscle contraction. Electromyography shows a characteristic decrease in amplitude of the evoked muscle action potential in response to an electrical stimulus.

Infant botulism, a condition confined to babies between 2 weeks and 9 months of age, typically presents with listlessness and generalized weakness (“floppy baby”) and has been shown to cause some cases of sudden infant death syndrome (SIDS). It has been associated with ingestion of various processed infant foods–honey in particular–that contain botulinum spores.