Epidemiology

Etiology

• Pathogen
  • Rabies is caused by several different members of the Rhabdoviridae family.
  • Rhabdoviruses are rod or bullet shaped
  • Genus: Lyssavirus
  • ssRNA
• Transmission
  • Most common animal reservoir worldwide: dogs
  • Most common animal reservoirs in the US: bats, raccoons, skunks, and foxes
  • Spread through saliva of rabid animal after bite injury
  • Via aerosols (e.g., bat caves); rare

Pathophysiology

Rabies virus binds the ACh receptor of peripheral nerves in the bite wound → migrates retrogradely along the axonal microtubules (using motor protein dynein) → enters the CNS → infects the brain

Clinical features

Encephalitic rabies (most common type)

• Hydrophobia: Rabies patients experience involuntary, painful pharyngeal muscle spasms when trying to drink; later on in the disease, the sight of water alone may provoke nausea or vomiting.
• CNS symptoms
  • Anxiety, agitation, and combativeness alternating with calm periods
  • Confusion and hallucinations
  • Photophobia
  • Fasciculations
  • Seizures
  • ↑ Muscle tone and reflexes with nuchal rigidity
• Autonomic symptoms (e.g., hypersalivation, hyperhidrosis)
• Coma and death within days to weeks of the development of neurological symptoms

Paralytic rabies (< 20% of cases)

• Flaccid paralysis, gradually ascending and spreading from bite wound
• Paraplegia and loss of sphincter tone
• Respiratory failure and death

Diagnostics

• Postmortem brain tissue autopsy
  • Histopathological findings: Negri bodies (eosinophilic cytoplasmic inclusion bodies typically found in the cerebellum and hippocampus)

Treatment

Prevention

Unvaccinated patients

• Rabies immune globulin (RIG)
  • Infiltrate as much RIG as feasible into and around the wound.
  • Inject the remaining RIG at a site distant from the site of vaccine administration.
• PLUS inactivated rabies vaccine