Updated: 7/9/2018

Rabies Virus and Infection

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Snapshot
  • A 10-year-old boy presents to the emergency room after being bit by an animal in a cave. His parents report that they live near some caves that the boy frequently explores. While they are not sure if it was a bat, they are concerned about rabies. On physical exam, there is a small excoriation on his left leg. Otherwise, physical exam is within normal limits. The boy is given the rabies vaccine and immunoglobulin.
Introduction
  • Classification
    • rabies virus
      • linear negative single-stranded RNA virus
      • rhabdovirus
      • 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
      • active immunization
    • rabies immunoglobulin
      • passive 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 polymerase chain reaction (RT-PCR)
      • 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
    • 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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Questions (3)

(M1.MC.17.4752) A 35-year-old spelunker presents to the emergency room complaining of one week of worsening malaise. His last solo spelunking trip was two months ago. While in the examination room, he asks to turn down the lights because they are too bright. His temperature is 101°F (38.3°C), blood pressure is 130/80 mmHg, pulse is 100/min, and respirations are 18/min. On examination he appears tremulous and agitated. He is oriented to person and place but not time. Which of the following pathogens is most likely responsible for this patient’s condition? Tested Concept

QID: 108810
1

(-) single-strand RNA virus

42%

(67/159)

2

(+) single-strand RNA virus

23%

(37/159)

3

Double-strand RNA virus

11%

(17/159)

4

Non-enveloped DNA virus

4%

(7/159)

5

Enveloped DNA virus

11%

(17/159)

L 2 C

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