Neurotoxic Clostridia

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Neurotoxic Clostridia

• Clostridium botulinum
• Clostridium tetani

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Clostridium botulinum

• Intoxication with serologically-distinct
  neurotoxins
• block acetylcholine release from cholinergic
  nerve endings
• cause neuroparalysis
• Spore in soil, on plants
• Ingested, germinate in gut vegetative cells
  cannot compete with flora
• Major problem has been ingestion of preformed
  toxin

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Clostridium botulinum

• Toxin produced in improperly prepared meat,
  vegetables, fruits
• spores not killed by boiling, survive inadequate
  pressure sterilization
• germinate in foods, vegetative cells produce
  toxin
• no visible spoilage, bad taste

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Clostridium botulinum

• Most cases associated with canned food not heated
  prior to consumption
• toxin destroyed (100C, 10 min)
• Not always canned food Virchow proposed
  Thüringer sausages as weapons in a duel

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Clostridium botulinum

• Spores germinate in animal carcasses or rotting
  vegetation
• produce enough toxin to cause disease outbreaks
  in ruminants, horses, mink, fowl
• carnivores, swine, fish occasionally affected

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Clostridium botulinum

• Botulism in humans shifted from intoxication to
  toxicoinfection
• infant botulism (floppy baby syndrome)
• Associated with variety of foods
• most common is honey
• spores microbiological bonus for bees
  collecting pollen and nectar
• low concentration of spores ( 0.25 spores per g)
  leads to disease in infants

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Clostridium botulinum

• Toxicoinfectious botulism
• increasing in users of illicit injected drugs
• particularly so-called black tar heroin
• especially when injection is intramuscular
  ("muscle popping")
• Wound botulism can also occur
• spores deposited in wound
• germinate, vegetative cells make toxin

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Botulism in Horses

• Most common with adulterated feed
• Shaker foal syndrome, spinal typhus
  toxicoinfectious

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Botulism in Poultry

• Type C in waterfowl, domestic poultry
• invertebrate larvae ingest toxin from carcasses,
  consumed by birds
• loss of ability to fly, drooping head
  (limberneck)
• chickens often have diarrhea
• Type E sporadic outbreaks due to consuming
  toxin-bearing fish
• dabbling ducks, shorebirds commonly affected
• annual mortality in migratory populations gt
  50,000

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Botulism in Cattle

• Pica in PO4-deficient animals
• ingest botulinum toxin with bones (lamziekte
  lame sickness)
• Poultry litter
• used as source of non-protein nitrogen
• toxin source dead birds
• outbreak in Queensland killed 20 of 30,000 cow
  herd
• deaths continued after feed removed?
• Facial muscle paralysis common

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Clinical Botulism in humans

• Toxin enters through GI tract
• absorbed, carried via blood stream
• attaches to presynaptic terminals of cholinergic
  nerves
• blocks neurotransmitter release, nerve impulses
  cannot be transmitted, muscles connected to
  nerves not stimulated
• Result generalized flaccid paralysis

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Clinical Botulism

• Symptoms 4 - 36 h post ingestion (varies with
  dose)
• weakness, dizziness, dryness of mouth
• nausea, vomiting, double vision
• anorexia, incoordination, blurred vision,
  dilation of pupils, inability to swallow
• ataxia, difficult speech
• death results from respiratory paralysis
• Mortality rate A 75, others 20

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Clinical Botulism

• Immunity
• Toxoid good immunogen
• Too many serotypes for routine, simple protection
• No immunity from clinical botulism immunizing
  dose is lethal
• Diagnosis detection of toxin by in vivo mouse
  test
• patient serum, food

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Clinical Botulism

• Therapy
• antitoxin, supportive therapy
• after toxin enters cells, therapy ineffective
• nerve regeneration may occur in survivors,
  frequent irreversible neurological damage
• Prevention
• care in home canning, heat food before ingestion
• immunize frequently-exposed laboratory workers
• toxoids for cattle

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Clostridium tetani - Tetanus

• Incidence
• 200 cases per year in US
• 350,000 cases per year worldwide
• Spores in soil, animal feces

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Clinical Tetanus

• Spores deposited in tissue
• wound, burn, ulcer, compound fracture, operative
  wounds, drug injection
• surgical incisions, docking, castrating, ear
  tagging wounds
• postpartum lesions in reproductive tract
• tetanus neonatorum infection of umbilical stump

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Clinical Tetanus

• Reduced oxygen, Eh (necrosis) usually required
• Mixed infections, foreign bodies contribute
• 10 year latency reported
• Incubation 24 h - 2 weeks
• shorter gt higher mortality
• varies with strain toxinogenicity, rate of toxin
  transfer to target tissues, host sensitivity

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Clinical Tetanus

• Spores germinate, vegetative cells lyse, release
  toxin
• Mild intermittent contractions near woun
• Retrograde, intraaxonal transport of toxin along
  peripheral motor nerves to CNS 20 mm/day
• Main target anterior horn cells of spinal cord,
  brain stem
• crosses synapse
• binds to presynaptic axonal terminals
• causes motor neuron hyperactivity
• sustained spasms in innervated muscles

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Clinical Tetanus

• Trismus (lockjaw), difficulty in chewing,
  swallowing
• Muscular tremor, increased stimulus response
• Impaired head and neck muscle function
• Death by interference with mechanics of
  respiration, usually without delirium
• Same basic pattern in domestic animals

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Clinical Tetanus

• Immunity single toxin, toxoid type
• Diagnosis clinical, toxin detection in mice
• Therapy antibiotics, antitoxin, surgery

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Botulinum and Tetanus Toxins

• Botulinum toxin
• A, B most common in US
• 28 grams of type A toxin LD for humanity
• C domestic animals, not humans
• D,E,F,G mainly outside US
• E often in fish
• Tetanus toxin
• nearly equal potency

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Botulinum and Tetanus Toxins

• 2-chain polypeptides, linked by disulfide bonds
• B (heavy) chain gt neurospecific binding, entry
  via receptor-mediated endocytosis
• A (light) chain zinc-dependent endopeptidase
• bond reduced in endosome, translocated to
  cytoplasm
• specifically attacks synaptic proteins
  (VAMP/synaptobrevin, syntaxin, SNAP-25)
• mediate exocytosis of neurotransmitters

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Botulinum and Tetanus Toxins

• Tetanus toxin, botulinum toxin types B, D, F, and
  G cleave VAMP/synaptobrevin
• membrane protein of synaptic vesicles
• Botulinum A, E toxins cleave SNAP-25
• component of presynaptic membrane
• Botulinum C toxin cleaves syntaxin
• protein of nerve plasmalemma
• Proteins conserved (yeast to humans), essential
  in docking, fusion events in cells
• End result blockage of acetylcholine release,
  muscle paralysis

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Tetanus ToxinMode of Action
Blockade of neurotransmitter (glycine and GABA)
release in the CNS
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Botulinum ToxinMode of Action
Blockade of neurotransmitter (acetylcholine)
release