Rabies usually presents as atypical encephalitis with preservation of consciousness; the disease may be difficult to recognize after the onset of coma. This disease, which usually leads to death despite aggressive therapy, has three phases.

• Prodrome: Pts have fever, headache, malaise, nausea, vomiting, and anxiety or agitation lasting 2-10 days. Paresthesias, pain, or pruritus near the site of exposure (which has usually healed at this point) is found in 50-80% of cases and strongly suggests rabies.
• Acute neurologic phase: Pts present with the encephalitic (furious) form of rabies in 80% of cases and with the paralytic form in 20%.
  • - Encephalitic form: Pts develop signs and symptoms common to other viral encephalitides (e.g., fever, confusion, hallucinations, combativeness, and seizures) that last 2-10 days. Autonomic dysfunction is common and includes hypersalivation, gooseflesh, cardiac arrhythmia, and/or priapism.
    • A distinguishing feature of rabies is prominent early brainstem dysfunction resulting in hydrophobia and aerophobia (involuntary, painful contraction of the diaphragm and the accessory respiratory, laryngeal, and pharyngeal muscles in response to swallowing liquid or exposure to a draft of air).
    • Hypersalivation and pharyngeal dysfunction produce characteristic foaming at the mouth.
    • Death usually occurs within days of brainstem involvement. With aggressive supportive care, late complications include cardiopulmonary failure, disturbances of water balance (syndrome of inappropriate antidiuretic hormone secretion or diabetes insipidus), and GI hemorrhage.
  • - Paralytic form: For unknown reasons, muscle weakness predominates but cardinal features of rabies encephalitis (hyperexcitability, hydrophobia, aerophobia) are lacking. Muscle weakness usually begins in the bitten extremity and proceeds to quadriparesis.
• Coma and death: Even with aggressive supportive measures, recovery is rare. Death usually occurs within 2 weeks.