Botulism¶

Chapter 158 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Bacterial · Chapter 158

Key Clinical Points¶

Botulism is a rare, life-threatening disease characterized by cranial nerve palsies and symmetric descending flaccid paralysis.
Four naturally occurring forms: foodborne, infant, wound, and adult intestinal colonization.
Botulinum neurotoxins (BoNTs) are metalloproteases that cleave SNARE-family proteins (SNAP-25, VAMP, syntaxin), inhibiting acetylcholine release.
Clinical presentation typically begins with ptosis (81%), followed by descending paralysis (93%) and respiratory compromise.
Diagnosis relies on clinical suspicion; mouse bioassay is the gold standard, while PCR/Endopep-MS are alternatives.
Equine botulinum antitoxin (BAT) treats non-infants; human-derived antitoxin (BabyBIG) treats infants.
Antitoxin prevents progression of paralysis but does not reverse existing paralysis.
No sensory deficits or fever; patients remain fully conscious with normal intellectual function.
Honey must never be fed to infants ≤1 year of age due to risk of infant botulism.
Recovery requires nerve regeneration and can take weeks to months.

1. DEFINITION & OVERVIEW¶

Botulism is a rare, life-threatening disease characterized by cranial nerve palsies and symmetric descending flaccid paralysis. The paralysis lasts for weeks or months → the time required for regeneration of affected nerve endings and recovery of voluntary muscle function.

• Key Clinical Features: ◦ No sensory deficits; patients are fully conscious with normal intellectual function.

• Four Naturally Occurring Forms: ◦ Foodborne botulism: Ingestion of preformed toxin in contaminated food. ◦ Infant botulism: Intestinal colonization by Clostridium botulinum spores in infants ≤1 year. ◦ Wound botulism: Germination of spores in wounds or necrotic tissue. ◦ Adult intestinal colonization: Similar to infant botulism but occurs in adults >1 year.

• Other Forms: ◦ Iatrogenic botulism: Systemic effects from BoNT injections. ◦ Inhalational botulism: Aerosolized toxin used as a bioweapon.

2. ETIOLOGY & PATHOPHYSIOLOGY¶

Botulism is caused by botulinum neurotoxins (BoNTs) produced by Clostridium botulinum, C. butyricum, and C. baratii.

• Serotypes: Seven serotypes (A–G) cause human disease; A, B, E, and F are the most common. • Genetic Basis: BoNTs are encoded by the bont gene; 40+ subtypes identified within serotypes A, B, E, and F.

• Lethal Dose Estimates: ◦ IV/IM: 0.1–1 ng/kg ◦ Inhalation: 1–75 ng/kg ◦ Oral: 0.1–1 μg/kg

3.1 Toxin Mechanism¶

Definition (Harrison's 22e): Botulinum neurotoxins are metalloproteases that cleave SNARE-family proteins, inhibiting acetylcholine release.

• Structure: ◦ Heavy chain: Responsible for receptor-binding and translocation. ◦ Light chain: Catalytic activity; cleaves specific proteins.

• Target Specificity: ◦ Serotypes A and E: Cleave SNAP-25. ◦ Serotypes B, D, F, G: Cleave VAMP. ◦ Serotype C: Cleaves SNAP-25 and syntaxin.

• Result: Disruption of synaptic fusion complexes → flaccid paralysis. Paralysis persists until nerve regeneration occurs.

3. EPIDEMIOLOGY¶

• Foodborne botulism: Third most common form in the US (mean 119/year); 64% are serotype A.

• Wound botulism: Second most common form (mean 24/year); 92% serotype A, 5% B; 96% linked to drug injection.

• Infant botulism: Most common form (2172 cases); 40% serotype A, 58% serotype B.

• Adult intestinal colonization: Rare; 63% serotype A or 27% serotype F.

• Table 158-1: Notable Foodborne Outbreaks (2001–2019): ◦ 2001 (Texas): Chili → 16 cases. ◦ 2015 (Ohio): Home-canned potatoes → 27 cases. ◦ 2015 (Mississippi): Pruno (illegal alcoholic beverage). ◦ 2017 (California): Nacho cheese → 10 cases.

4. CLINICAL FEATURES¶

• Initial Presentation: Ptosis (81%) followed by descending flaccid paralysis (93%).

• Cranial Nerve Involvement: ◦ III, IV, VI, VII: Ptosis, diplopia, facial palsy. ◦ IX: Dysphagia and regurgitation.

• Autonomic Dysfunction: Anhidrosis, paradoxical secretions.

• Respiratory Impact: 65% experience shortness of breath; 42% require mechanical ventilation at admission.

• Symptom Frequencies (332 cases): ◦ Difficulty swallowing: 86%" ◦ Fatigue: 85%" ◦ Blurred vision: 80%" ◦ Slurred speech: 78%" ◦ Double vision: 76%" ◦ Limb weakness: 78%" ◦ Alert and oriented: 93%" ◦ Afebrile: 99%"

4.1 Clinical Manifestations¶

• Cranial nerves: Ptosis, diplopia, facial palsy (III/IV/VI/VII).

• Gastrointestinal: Dysphagia, regurgitation (IX), constipation (due to intestinal paralysis).

• Other: Nausea/vomiting (specific to foodborne cases).

5. DIFFERENTIAL DIAGNOSIS¶

• Guillain-Barré syndrome (GBS): Ascending paralysis eq descending; elevated CSF protein.

• Myasthenia gravis: Positive Tensilon test; rapid nerve stimulation.

• Lambert-Eaton syndrome: Proximal weakness in cancer patients.

• Stroke: Asymmetric paralysis; upper motor neuron signs.

• Botulism-specific features: ◦ Normal CSF protein. ◦ No brain imaging abnormalities. ◦ Neuromuscular junction blockage on EMG.

6. INVESTIGATIONS & DIAGNOSIS¶

Clinical Evaluation: Assess for ptosis, dysarthria, and descending paralysis.
Public Health Notification: Contact CDC/state health department → request antitoxin and initiate specimen collection.
Laboratory Confirmation: ◦ Mouse bioassay: Gold standard (detects BoNT in serum, stool, or food). ◦ Alternative methods: PCR or Endopep-MS for serotyping.

6.1 Diagnostic Algorithm¶

Clinical evaluation for ptosis, dysarthria, and descending paralysis.
Contact CDC/state health department → request antitoxin and initiate specimen collection.
Confirm with mouse bioassay or PCR/Endopep-MS.

7. MANAGEMENT & TREATMENT¶

Antitoxin Therapy: ◦ Equine BAT: Administered to non-infants (from CDC stockpile, no charge). ◦ BabyBIG: Human-derived; licensed for infant botulism only. ◦ Note: Antitoxin prevents progression → does not reverse existing paralysis.
Supportive Care: ◦ Respiratory Support: Mechanical ventilation (66% of patients require intubation). ◦ ICU Management: Treatment for pressure ulcers, hydration, and psychological care.

7.1 Antitoxin Therapy¶

• Equine BAT: Administered via CDC stockpile (no charge).

• BabyBIG: Licensed for infant botulism only.

8. PROGNOSIS & COMPLICATIONS¶

• Recovery Timeline: Weeks to months required for nerve regeneration.

• Survival Rates: ◦ Non-infant cases: 95% recovery rate. ◦ Infant botulism: Near 100% survival.

• Complications: ◦ Ventilator-associated pneumonia. ◦ Decubitus ulcers. ◦ Psychological trauma from prolonged ICU stay.

9. SPECIAL CONSIDERATIONS¶

• Infant Prevention: Honey must never be fed to infants ≤ 1 year of age.

• Food Safety: Proper home canning (acidic foods, high heat) and awareness of local risks (e.g., Alaskan Native food traditions).

10. KEY PEARLS & CLINICAL TRAPS¶

• Diagnostic Clues: Ptosis + descending paralysis = high suspicion.

• Differentiation: Normal CSF protein and lack of imaging abnormalities distinguish from GBS/Stroke.

• Exclusion Criteria: No sensory deficits, no fever, no brain imaging abnormalities.

• Antitoxin Timing: Must be administered early to stop progression; it does not reverse existing paralysis.

Reference Tables¶

TABLE 158-1 Total Foodborne Botulism Outbreaks of 10 or More Cases Reported in the United States Between 2001 and 2019…¶

Harrison's 22e, p.1234

YEAR	STATE	FOOD SOURCE	NO. OF CONFIRMED CASES
2001	Texas	Chili	16
	Multistate	Commercially canned hot dog chili sauce
2015	Ohio	Home-canned potatoes used to prepare a potato salad, served at a church potluck	27
	Mississippi	Pruno, illegal alcoholic beverage consumed by persons who were incarcerated at a federal facility
2017	California	Commercially produced nacho cheese, sold at a convenience store	10