Updated: 8/5/2018

Rabies

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Snapshot
  • A 13-year-old boy in rural Asia presents to a local hospital after a dog bite. The dog did not belong to anybody and is often seen running around the area. His parents report that this occurred a few weeks ago, but that they weren’t concerned until the boy started having low-grade fever and chills. While the physician explains that they can administer both active and passive immunity, as symptoms have already started, the parents must prepare for the worst.
Introduction
  • Classification
    • rabies virus 
      • a negative single-stranded linear RNA virus
      • a rhabdovirus
      • a helical capsid and bullet-shaped
    • transmission
      • via bites from infected animals
        • developed countries
          • bats > raccoons, and skunks > dogs
        • developing countries
          • dogs > others
      • via aerosol transmission (rare)
        • bats
  • Epidemiology
    • demographics
      • more common in children
      • majority of cases are in Asia and Africa
    • risk factors
      • interaction with non-domestic animals
  • Pathogenesis
    • long incubation period (weeks to months)
    • replicates in muscle and binds to the nicotinic acetylcholine receptor
      • retrograde migration to central nervous system via dynein motors 
  • Associated conditions
    • encephalitic rabies (more common)
    • paralytic rabies
  • Prevention
    • whole virus inactivated vaccine
      • passive immunization
    • rabies immunoglobulin
      • active immunization
  • Prognosis
    • most cases, without early intervention, lead to coma and death within weeks
Presentation
  • Symptoms
    • nonspecific prodrome
      • malaise
      • fever
      • headache
  • Physical exam
    • fever
    • encephalitic rabies
      • hydrophobia
        • muscle spasms when offered water
        • leads to “foaming at the mouth”
      • photophobia
      • autonomic dysfunction
        • excess sweating
        • piloerection
        • hypersalivation
      • agitation
      • seizures
    • paralytic rabies
      • quadriparesis
      • bilateral facial weakness
    • late stage disease
      • paralysis
      • coma
      • death
Studies
  • Labs
    • viral studies
      • reverse transcription and polymerase chain reaction
      • isolation of virus
  • Histology
    • brain biopsy
      • performed post-mortem
      • negri bodies 
        • eosinophilic inclusion bodies in cerebellar Purkinje cells and hippocampal neurons
        • pathognomonic
  • Making the diagnosis
    • based on clinical presentation
Differential
  • Botulism
    • distinguishing factor
      • flaccid paralysis without other signs of encephalopathy
  • Temporal lobe (herpes simplex virus-1) encephalitis 
    • distinguishing factor
      • disinhibited behaviors such as hyperphagia, hypersexuality, and hyperorality
Treatment
  • Management approach
    • give post-exposure prophylaxis immediately
      • when bitten by rabid animal
      • when bite cannot be ruled out
      • if the animal is domestic observe the animal for 24-48 hours
    • once patients are symptomatic, there is no treatment and patients should receive supportive care
      • pain management
      • sedation
  • Conservative
    • wound cleaning
      • indication
        • post-exposure
  • Medical
    • rabies immunoglobulin
      • indication
        • post-exposure prophylaxis
Complications
  • Respiratory failure leading to death

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