Rabies (Encephalitic)

Encephalitic (furious) rabies is an almost invariably fatal acute viral encephalitis caused by rabies virus (RABV), accounting for ~80% of clinical rabies cases. [1] It is characterized by fluctuating consciousness, hydrophobia, aerophobia, inspiratory spasms, and autonomic dysfunction, progressing to coma and death typically within 5–7 days of symptom onset without intensive care. [2] Approximately 59,000 human rabies deaths occur annually worldwide, with 98% linked to canine exposures. [3-4]

The following figure illustrates the pathogenic journey of RABV from initial bite inoculation through neuromuscular junction entry, CNS invasion, and centrifugal spread to salivary glands:

• Exposure history is the single most critical element: animal bite (dog, bat, raccoon, skunk, fox), scratch, or mucous membrane contact with saliva — may have occurred weeks to months prior [6]
• Ask about geographic location, travel to rabies-endemic regions (Asia, Africa), occupation (veterinarian, animal handler, cave explorer), and outdoor/recreational activities [4][7]
• Prodromal symptoms (2–10 days): fever, malaise, headache, nausea, sore throat — nonspecific and easily missed [2][8]
• Pain, paresthesia, or pruritus at the bite site is often the earliest neurological symptom and is highly suggestive [2][8]
• Progression to agitation, anxiety, confusion, hallucinations, hypersalivation, difficulty swallowing
• Hydrophobia: pharyngeal spasms triggered by sight, sound, or perception of water [6][8]
• Aerophobia: spasms triggered by air drafts
• Periods of agitation alternating with lucidity — a key feature of furious rabies [8]
• In the US, rabies diagnosis is almost always missed at the first clinical encounter because exposure history may be remote or unrecognized, particularly with bat exposures [6][9]

• Hydrophobia or aerophobia — virtually pathognomonic for rabies [2][10]
• Inspiratory muscle spasms (spontaneous or provoked)
• Rapidly progressive encephalitis with autonomic instability (tachycardia, hypersalivation, hyperpyrexia, piloerection)
• Fluctuating consciousness with episodes of extreme agitation
• Cardiac arrhythmias — supraventricular arrhythmias, heart block, myocarditis mimicking STEMI [11-13]
• Seizures, delirium, or coma
• Any acute encephalitis in a patient with a history of animal bite in an endemic area

• No effective antiviral therapy exists once clinical symptoms develop [1][14-15]
• Milwaukee Protocol (therapeutic coma + ketamine + ribavirin + amantadine): now considered ineffective with at least 64 documented failures; should be abandoned [14-16]
• Ribavirin and interferon-α have been disappointing [15]
• Minocycline and corticosteroids should NOT be used — may aggravate disease [15]
• Ketamine and midazolam are used for symptom palliation (sedation, dysautonomia control) rather than as curative therapy [2]
• Nimodipine has been added in some protocols for vasospasm but carries risk of severe hypotension; use with extreme caution [2]
• Post-exposure prophylaxis (PEP) is the only effective intervention and must be given before symptom onset:
  • Unvaccinated: wound cleansing + HRIG 20 IU/kg infiltrated into wound + rabies vaccine IM on days 0, 3, 7, 14 (4-dose ACIP schedule) [17-18]
  • Previously vaccinated: 2 doses on days 0 and 3, no HRIG [17]

• Dysphagia is a cardinal feature — patients cannot swallow due to pharyngeal spasms; oral intake is impossible once hydrophobia develops [8][10]
• IV hydration and nutritional support are required
• No specific dietary triggers or long-term dietary management apply

• Neurological: altered mental status, agitation, hallucinations, seizures, focal deficits, cranial nerve palsies (especially in bat-acquired cases), myoclonus, tremor [2][19]
• Respiratory: inspiratory spasms, periodic/ataxic breathing, respiratory arrest [10][13]
• Cardiovascular: palpitations, chest pain (myocarditis), arrhythmias [11][13]
• GI: nausea, vomiting, hypersalivation, GI bleeding [10]
• Autonomic: diaphoresis, piloerection, priapism, lacrimation, pupillary abnormalities
• Endocrine: diabetes insipidus, SIADH, hypothalamic-pituitary dysfunction [20-21]
• Musculoskeletal: fasciculations, weakness at bitten extremity

• Collateral history is essential: witnesses to animal exposure, travel companions, family members who may recall a bite the patient has forgotten or dismissed
• Children may not report bat contact or minor bites [6]
• Bat exposure may be unrecognized (e.g., bat found in room of sleeping person) [17]
• No hereditary predisposition; family history is not contributory
• Organ/tissue transplant history — rare cases of transmission via transplanted corneas and organs [17]

• Dog bite in Asia or Africa — accounts for ~98% of global human rabies [4][22]
• Bat exposure in the Americas — most common source in the US (70% of indigenously acquired cases) [9]
• Bites to highly innervated areas (face, hands) or deep muscle bites increase transmission efficiency [2][6]
• Proximity of bite to CNS (head, neck) may shorten incubation period [6]
• Children — higher risk due to inquisitive behavior, smaller stature (more head/face bites), and failure to report exposures [6]
• Failure to receive or complete PEP [3]
• Occupational exposure: veterinarians, animal control workers, laboratory workers, cave explorers [4]
• Travel to endemic regions without pre-exposure prophylaxis [22]

• Tetanus — trismus (lockjaw), opisthotonus, sustained muscle rigidity (vs. intermittent spasms in rabies); no altered consciousness until late [10]
• Herpes simplex encephalitis (HSV-1) — temporal lobe predilection on MRI, hemorrhagic changes; no hydrophobia [7][23]
• Other viral encephalitides (arboviral, enteroviral, VZV) — distinguished by epidemiology, CSF findings, MRI patterns [7][24]
• Autoimmune encephalitis (anti-NMDAR, LGI1) — more subacute onset, psychiatric features, seizures; antibody testing differentiates [23][25]
• Guillain-Barré syndrome — mimics paralytic rabies; ascending weakness without altered consciousness [2]
• Delirium tremens — alcohol withdrawal history, tremor, hallucinations; no hydrophobia [10]
• Hysterical pseudohydrophobia — psychogenic; no autonomic dysfunction or progression [10]
• Postvaccinal encephalomyelitis — history of nervous-tissue rabies vaccine (older formulations) [10]
• Cerebral malaria, bacterial meningitis — in endemic settings, consider concurrent infections

• Prior rabies vaccination status — critical for determining PEP regimen and prognosis; most survivors had received at least partial vaccination before symptom onset [8][16]
• Previous animal bites or PEP courses
• Immunocompromised states (HIV, chemotherapy) — may alter immune response and PEP efficacy; immunocompromised patients should receive 5-dose PEP schedule [18]
• History of organ transplantation (rare transmission route) [17]
• No specific chronic illnesses predispose to rabies, but immunosuppression may impair viral clearance

• Vital signs: tachycardia, hypertension or hypotension, hyperpyrexia, irregular respirations [10][13]
• Inspection of bite wound: look for healing bite marks, especially on extremities, face, or hands; may show local inflammation
• Neurological exam:
  • Fluctuating level of consciousness with periods of lucidity and agitation [2]
  • Hydrophobia test: offering water provokes visible pharyngeal spasms and terror [8]
  • Aerophobia test: blowing air on face triggers spasms
  • Hypersalivation ("foaming at the mouth")
  • Cranial nerve palsies (more common in bat-acquired cases) [19]
  • Myoclonus, tremor, fasciculations
  • Late: flaccid paralysis, areflexia, coma [2]
• Autonomic signs: piloerection, diaphoresis, pupillary dilation, priapism, lacrimation
• Cardiac: irregular rhythm, signs of heart failure (myocarditis) [11][13]
• Myoedema (mounding of muscle on percussion) — seen in paralytic form [2]

• Routine labs: plasma neutrophil leukocytosis; otherwise often unremarkable [26]
• CSF: mild lymphocytic pleocytosis in only ~60% of patients in the first week; mildly elevated protein (more pronounced in bat-acquired cases); normal glucose [19][26]
• Antemortem diagnostic panel (contact CDC or public health lab): [6][27]
  • Saliva: RT-PCR for RABV RNA (sensitivity ~86%) [28]
  • Nuchal skin biopsy (nape of neck, hair follicle-containing): immunohistochemistry for rabies antigen in cutaneous nerves [6][27]
  • Serum and CSF: rabies virus neutralizing antibody (RFFIT) — in unvaccinated patients, CSF antibody confirms diagnosis [6]
  • CSF: RT-PCR for RABV RNA (sensitivity ~45% antemortem, higher postmortem) [28]
• Sequential sampling is indicated if initial tests are negative but clinical suspicion remains high [6]
• Neurofilament light chain (NfL): emerging biomarker — significantly elevated in rabies vs. other encephalitides [29]
• No single test is sufficient for antemortem diagnosis; multiple specimen types are required [27]

• MRI brain (preferred over CT): [2][30]
  • Non-comatose phase: subtle, ill-defined T2/FLAIR hyperintensities in brainstem, hippocampi, hypothalami, deep/subcortical white matter — without gadolinium enhancement (a distinguishing feature from other viral encephalitides) [2][30]
  • Comatose phase: more widespread T2 hyperintensities; gadolinium enhancement may appear along brainstem and midline structures [2]
  • Brachial plexus enhancement on the bitten side may be seen even during prodrome [2]
  • Novel findings include dentate nuclei involvement, cranial nerve enhancement, "hot cross bun" sign in pons [31]
• CT head: low sensitivity; may show only diffuse edema in late stages
• The lack of contrast enhancement in a noncomatose encephalitis patient should raise suspicion for rabies over other viral encephalitides [30]

The following MRI demonstrates characteristic brainstem T2 hyperintensities in a confirmed case of rabies encephalitis:

• Direct fluorescent antibody (DFA) test: gold standard for postmortem diagnosis on brain tissue; detects rabies antigen [27]
• Negri bodies: eosinophilic cytoplasmic inclusions in hippocampal and cerebellar Purkinje neurons — pathognomonic on histopathology [32]
• Virus isolation from saliva [27]
• WHO clinical case definition: acute neurologic syndrome dominated by hyperactivity (furious) or paralysis, progressing to coma and death within 7–10 days [6]
• Animal testing: if the biting animal is available, DFA testing of brain tissue; 10-day observation period for dogs, cats, and ferrets [8][17]

• Cardiac involvement is common and clinically significant [1][11][13]
• Supraventricular arrhythmias (most common cardiac finding) [13]
• ST-segment elevation mimicking STEMI — due to interstitial myocarditis, not coronary occlusion [11]
• Heart block (including complete heart block) — may be the terminal event [12]
• Autonomic denervation manifests as loss of heart rate variability [33]
• ECG should be obtained in all suspected cases; continuous telemetry monitoring is essential
• Vagus nerve neuritis found at autopsy explains many of the cardiac manifestations [12]

• Encephalitic rabies is a clinical diagnosis supported by exposure history and confirmed by specialized laboratory testing [6]
• Average survival from symptom onset to death: 5.7 days (furious form) without intensive care [2]
• Only ~34 well-documented survivors exist; most had received partial vaccination and/or were infected with bat RABV variants; many had severe neurological sequelae [8][14]
• The disease is almost 100% fatal once clinical signs appear [1][5]
• Atypical presentations (focal brainstem signs, myoclonus, hemichorea, Horner syndrome) are more common with bat RABV variants and contribute to frequent misdiagnosis [2][34]
• Complications in ICU-managed patients include ARDS, diabetes insipidus, myocarditis, GI bleeding, and multi-organ failure [1][20]

Initial stabilization

• Airway management — early intubation may be needed for inspiratory spasms and airway protection
• IV access, continuous telemetry, ICU admission
• Aggressive sedation with benzodiazepines (midazolam) and ketamine for agitation, spasms, and dysautonomia [2]
• Avoid neuromuscular paralysis if possible (masks clinical progression)

Definitive management

• No proven curative therapy exists [1][14-15]
• Decision between aggressive critical care vs. palliative approach should be made early with the patient's family:
  • Favorable factors for aggressive approach: prior partial vaccination, young age, immunocompetent, bat RABV variant, early neutralizing antibody detection, mild neurological disease at presentation [8]
  • Palliative approach: liberal sedation (midazolam, opioids) to relieve suffering; appropriate for most cases, especially canine RABV variant [2][8]
• Milwaukee Protocol should no longer be used — at least 64 failures documented [14]
• Manage complications: vasopressors for hemodynamic instability, antiarrhythmics, correction of DI/SIADH, ventilatory support

PEP (pre-symptom only)

• Wound cleansing with soap/water for ≥15 minutes + povidone-iodine [3][8]
• HRIG 20 IU/kg infiltrated into and around wound [17]
• Rabies vaccine IM: days 0, 3, 7, 14 (4-dose schedule per ACIP) [18]

• All suspected rabies cases require ICU admission once neurological symptoms develop [1][8]
• Strict contact and droplet precautions for healthcare workers; PEP for any staff with mucous membrane or open wound exposure to patient saliva [17]
• Rabies is a nationally notifiable disease — immediate notification to local/state public health department and CDC [6]
• Infectious disease and neurology consultation
• Palliative care consultation when aggressive treatment is not pursued or deemed futile
• No role for observation unit or outpatient management once symptomatic

For exposed but asymptomatic patients receiving PEP

• Complete the full vaccine series on schedule (days 0, 3, 7, 14) [18]
• Return immediately for any neurological symptoms: paresthesia at bite site, anxiety, agitation, difficulty swallowing, fever with behavioral changes
• Wound care follow-up; monitor for secondary bacterial infection

For symptomatic patients

• Prognosis is nearly uniformly fatal; family counseling and goals-of-care discussions are paramount [1][14]
• Rare survivors require prolonged neurorehabilitation; most have significant neurological sequelae [8][14]
• Healthcare workers exposed to patient secretions should receive PEP evaluation

Public health follow-up

• Ensure the biting animal is captured for testing or observation if possible [8]
• Contact tracing for other potential exposures from the same animal source

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