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Snapshot
  • A 50-year-old male presents to the ED with dysphagia, hypersalivation, agitation, and generalized muscle twitching. Past medical history revealed patient had right arm pain and paraesthesia one week prior which had failed to resolve. Further questioning revealed the patient had been bitten by a racoon about three months ago while hiking in the woods. He didn't seek medical attention. During physical exam, the patient experienced cardiac arrythymia and hypotension and was resuscitated  and mechanically ventilated. CT scan and lumbar puncture were unremarkable. Nuchal biopsy was carried out and samples of the patient's saliva and serum sent for DFA and PCR.
Introduction
  • Classification
    • virus
      • RNA
        • negative-stranded
          • rhabdovirus
            • rabies
  • Pathogenesis
    • transmission
      • animal bite
      • animal contact
      • aerosol
      • corneal/organ transplant
    • reservoir
      • U.S. most commonly
        • bats
        • raccoons
        • skunks
      • internationally most commonly
        • dogs
    • molecular biology
      • virus binds to peripheral nicotinic ACh receptors
      • virus travels up axons to DRG via retrograde axoplasmic transport 
      • virus enters the spinal cord and rapidly infects the brain
  • Incubation period is weeks to months
    • allows for immunization after exposure
  • Characteristics
    • RNA
      • single-stranded
      • negative-sense
      • linear
    • bullet shaped capsid
    • envelope
    • helical
Presentation
  • Symptoms
    • fever and flu-like malaise
    • agitation
    • photophobia
    • hydrophobia
      • brainstem infection leads to painful contractions of pharyngeal muscles when swallowing liquids
      • leads to "foaming at the mouth"
    • seizures
    • disorientation
    • hallucination
    • paralysis
    • coma
    • death
      • secondary to respiratory dysfunction
Evaluation
  • Negri bodies 
    • collections of virions in the cytoplasm
    • typically occur in the hippocampus and cerebellum
    • pathognomonic
  • Diagnosis
    • clinical
    • Negri bodies on brain biopsy
    • DFA, PCR
Differential
  • Herpes simplex encephalitis
  • Seizure disorders
  • Psychosis
  • Tetanus
Treatment
  • Prophylaxis following exposure
    • if bitten by a rabid animal (or a bite cannot be ruled out), stimulate immune response while the virus is still in its incubation phase via 
      • human rabies immunoglobulin (hRIG)
        • passive immunization
      • 5 doses of killed rabies virus vaccine
        • active immunization
Prognosis, Prevention, and Complications
  • Prognosis
    • active rabies is nearly always deadly
    • only 1 confirmed case of recovery
  • Prevention
    • killed rabies vaccine
    • indication
      • animals
      • high-risk individuals
  • Complications
    • cardiac arrest
    • respiratory failure
    • acute renal failure
 

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