Rabies

Epidemiology

  • Only 9 reported cases in USA between 1908-1993
  • Risk factor: bat exposure (present in 7/9 cases reported)

Pathogenesis

  • Transmission
    • Accidental release of aerosolized Rabies virus in laboratory
    • Inhalation of aerosolized Rabies virus from bat feces
    • Animal bite
  • Invasion of neurons -> retrograde spread via neurons at 3 mm/hr to ward brain -> infection of brain -> centrifugal spread to autonomic and peripheral nervous system
    • In final stages of infection, migrates to salivary glands -> shed in saliva (via bites)

Diagnosis

Neck full thickness skin Bx (including as many hair follicles as possible): useful in the early stage/stain with IF-anti Rabies Ab
-Positive in 50% during first week (higher sensitivity later in disease course)

Brain Bx: may be normal (although cortical Bx may be positive)

LP:
-Rapid fluorescence focus inhibition test: measures CSF Rabies-neutralizing Ab, which appears in CSF on > day 8 of illness

Culture of saliva/ CSF/ brain/ urine/ tracheal secretions: low sensitivity for Rabies virus


Clinical

Clinical Stages:
-Prodrome (lasts 2-10 days): fever/ chills/ anorexia/ cough/ abdominal pain/ N/V/D/ malaise
-Acute neurologic phase:
–Furious type (80% of cases): hyperactivity/ altered MS/ hallucinations/ autonomic instability (hyperthermia/ tachycardia/ HTN/ hypersalivation)
–Paralytic type (20% of cases): paralysis (often in the bitten extremity/ may ascend and mimic GBS)/ coma and respiratory arrest (may occur within 10 days of symptom onset)


Treatment

Pre-exposure prophylaxis (for high risk groups, like spelunkers or travelers to endemic areas, such as India):
1) Rabies vaccination:
-Concurrent mefloquine or chloroquine may interfere with intradermal vaccine efficacy

Post-exposure prophylaxis:
1) Local wound treatment:
2) Rabies immune globulin: recent shortages
3) Rabies vaccination:


Prognosis

  • Once symptoms occur, Rabies has the highest case-fatality rate of any known human infection

References

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