Organism:
• Gram positive, large rod shaped, bacillus
• Strictly anaerobic conditions required for growth
• Ability to undergo sporulation to survive adverse conditions
o Sub-terminal spore, ovoid shape
• 7 serotypes of toxins
• 4 physiological groups
o Group 1: proteolytic, produces A,B and F type toxins. Disease causing in humans
♣ Growth optimally between 30-37 degrees Celsius
o Group 2: non-proteolytic, produces B,E, and F, can causes disease in humans
♣ Optimally grows between 25-30 degrees Celsius
o Group 3: producers of C,D type toxin, primarily infectious in animals
♣ Growth optimally between 30-37 degrees Celsius
o Group 4: produce G toxin.
♣ Growth optimally between 30-37 degrees Celsius
Mode of Transmission:
• Primarily routine Foodborne transmission
• Foodborne botulism: acquired through the ingestion of preformed toxins within food
• Infant botulism: acquired by ingestion of C. botulinum spores, which germinate into vegetative bacteria given suitable conditions of undeveloped infant GI tract.
• Wound botulism: acquired by contamination of open wound or abscess with spores of botulinum
• Rare forms:
o Inhalation: accidental events which toxin is aerosolized and inhaled and will cross alveolar epithelium
• NO PERSON TO PERSON TRANSMISSION
Virulence Factors:
• Progenitor toxin with toxogenic and non-toxogenic components
o Non-toxogenic component: includes neurotoxin subunit with hemagglutinin activity (HA). To protect toxin from harsh conditions inside host ie. Low pH
o Toxogenic component: includes parts responsible for translocation of toxins across synaptic membrane and cleaving activity
♣ 150 kDa single chain progenitor toxin initially synthesized, transformed into dichain structure when it is nicked
• 100 kDa heavy chain – facilitates receptor binding and receptor mediated endocytosis + translocation
• 50 kDa light chain – zinc-dependent metalloprotease, that is catalytic, helps cleavage of SNARE proteins
• 7 Serogroups (BoNT) – targeting differing synaptic vesicle associated proteins
o Type A = most potent
o Botulinum neurotoxin (BoNT) A,C and E cleaves synaptosomal associated protein (SNAP-25)
o BoNT C – cleaves syntaxin as well
o BoNT B,D,F,G cleaves synaptobrevin
• Heat resistant spores, help survival in environment for long periods of time, increasing probability of infecting
Mechanism of Pathogenesis:
• Infection begins with ingestion of preformed toxins or spores
o If spores, germination in GI tract (due to undeveloped microflora) – subsequent in vivo production of toxins
o If wound botulism, germination within appropriate anaerobic conditions of wound/abscess that allows toxin production
• Enters bloodstream and transported to peripheral cholinergic synapses including neuromuscular junctions.
• Internalized inside vesicle
• Progenitor toxin is cleaved into dichain and light chain is translocated into cytosol
• Light chain acts to cleave specific proteins that are part of the SNARE complex (SNAP-25, syntaxin & synaptobrevin) associated with fusion of vesicle to plasma membrane
• Therefore, inhibiting neurotransmitter (acetylcholine) release from vesicles
• Resulting in flaccid paralysis in motor system
Symptoms & Disease effects:
Common for all botulism: symmetric cranial nerve palsies and also symmetric descending flaccid paralysis
Foodborne:
• Onset: 12-36 hours
• Initial symptoms: similar to GI disease ie. Vomiting, nausea, diarrhea, however caused from other contaminants within food and not botulinum itself
• Diplopia (double vision), ptosis (drooping eyelids), dry mouth, slurred speech, muscle weakness, descending symmetric paralysis
Infant:
• Constipation, lethargy, weak cry, loss of head control, weak suck/inability to feed, decreased spontaneous movement
• increased drooling probably due to dysphagia (inability or discomfort when swallowing)
Wound:
• onset: approx. 2 weeks later than foodborne
• similar symptoms to foodborne botulism but lacks gastrointestinal disease symptoms
• wound may appear to be healing well, but neurological manifestations still occur
If paralysis progresses to respiratory musculature (intercostal muscles, diaphragm), may cause death, due to inspiration inability and insufficient amounts of oxygen inhaled.
A weakened glottis may also cause airway obstruction
Diagnostics:
• conventionally to demonstrate toxins in stool, serum, gastric secretions, food samples,
• Mouse bioassay (gold standard)
o Intraperitoneal injection of sample into mouse, wait and observe if symptoms arise that indicate botulism ie. Respiratory distress and muscle weakness
o Toxin type determination:
♣ Inject previously infected mouse with specific antitoxins and observe which neutralizes the type injected before
o Very sensitive, however labor and resource intensive, so is not available everywhere
• ELISA
o Format to detect botulinum neurotoxins
o Clinical specimens may interfere with ELISA reactions
o Sensitivity is much lower, overall considered inferior
• Endopeptidase Assay
o Detects active neurotoxins based on specific cleavage SNARE proteins
o Fluoresces when specific proteins have been cleaved
o Requires expensive equipment and specialized skills so not used often
• Culture:
o To assist diagnosis, hard to isolate/culture due to strict anaerobic conditions
• PCR and Mass spectrometry
o Being explored due to rapid diagnosis and potentially greater sensitivity, reproducibility an issue between labs
Treatment:
• Appropriate airway and ventilation management (supportive therapy) crucial for those with potential paralysis – rapid diagnosis essential
• Heptavalent botulinum antitoxin (HBAT) – equine derived intravenous infusion
o Neutralizes toxins not yet bound, to minimize nerve damage and disease severity
o Does no reverse paralysis if it already occurred
o Perform skin sensitivity test beforehand – (potential hypersensitivity) if erythema at site, proceed with lowest possible rates of infusion and observe response of patient to HBAT
o BabyBIG for infants
• Surgical debridement (wound botulism)
• Antibiotics: primarily for secondary infections
o Avoid aminoglycosides and tetracyclines – potentiates inhibition of acetylcholine release
Prevention: adherence to safe methods of home canning, boiling/heating to 85 degrees Celsius to inactivate heat labile toxins, prevent ingestion of honey by infants, treatment of wounds early, avoid bulging cans.
Problems/potential benefits for healthcare:
• Problem: Increasing rates of wound botulism due to rise of intravenous drug users and “skin popping” (injection of “black tar heroin” subcutaneously rather than veins)
• Benefits:
o Used to treat many neurological disorders, ie. Cervical dystonia, spasticity, blepharospasm
o Inject toxins directly into overactive muscles to prevent neuromuscular signaling
o Side effects usually transient and mild