RABIES ENCEPHALITIS
History
• Possible h/o dog, cat, or other nonrodent (raccoon, skunk, fox, bat) bite or scratch or rabid-appearing animal (agitated, drooling, unprovoked attack) or bat exposure
• Prodrome lasts 2–10 d; nonspecific fevers, pharyngitis, HA, anorexia, pain, N/V, anxiety, irritability or paresthesias at site of bite or scratch
Findings
• Hydrophobia, aerophobia, high fevers
• CNS sxs begin 2–7 d after start of prodrome
• 80% hyperactivity (agitation, thrashing, bulbar, & myoclonus), 20% “dumb rabies” (progressive, ascending, flaccid paralysis w/ intact sensorium, incontinence)
• Progressive autonomic instability: Hyperpyrexia, mydriasis, ↑ lacrimation & salivation
• Late findings: Hypotension, coma, DIC, multisystem organ failure, arrhythmias, & arrest
• Rapidly progressive encephalopathy
• Paralysis & apnea are terminal events; universally fatal unless pt gets prophylaxis
Evaluation
• Rabies antigen, RNA, rabies-neutralizing Ab titer >1:5 in serum is diagnostic of infection if not previously vaccinated (4× ↑ in titers diagnostic for vaccinated pts)
• CSF: ↑ protein; slightly ↑ RBC & WBC; Ab titer diagnostic, regardless of vaccine status
• CT head, CSF Gram stain & culture; evaluate for other causes of encephalopathy
Treatment
• Supportive, palliative
• No proven medical tx has been shown to be effective
• Therapeutic coma (ketamine, benzo’s) & antiviral therapy (amantadine, ribavirin) rarely a/w survival
Disposition
• ICU admission if neuro or resp sxs w/ inpt ID consult
• Notify public health department & animal control center
• Identify others at risk & initiate postexposure prophylaxis if indicated
Pearls
• Caused by Lyssavirus in family Rhabdoviridae
• Dogs are the most commonly infected animals worldwide, but very rare in US & Canada
• All 3 reported cases of neurologically intact survivors of rabies received rabies vaccine before onset of sxs
• Human-to-human transmission through corneal transplants (8 cases), organ transplants (8 cases), airborne through lab work (2 cases), & human bites (1 case)
• Initial ED presentation of active rabies is rare, nonspecific, almost always missed; universal precautions should be used in all pts w/ unexplained encephalopathy
• Accounts for >35000 deaths/y in developing countries, consider when neurologic sxs occur after foreign travel (esp South East Asia, Africa, Latin America)
• Nearly always fatal once sxs develop. Prevention is key! Prophylaxis always successful.
RABIES POSTEXPOSURE PROPHYLAXIS
History
• Report of dog, cat, or other nonrodent (raccoon, skunk, fox, bat) bite or scratch or rabid-appearing animal (agitated, drooling, unprovoked attack)
• Any contact w/ bat, dead or alive
Findings
• Bite wound or scratch mark, possibly no signs of trauma
Evaluation
• Consider contacting local public health authority to assess rabies exposure risk
Treatment
• Wound care (soap, water, irrigation w/ povidone–iodine solution), débridement of devitalized tissue, secondary closure, update Tetanus vaccination
• If domestic dog or cat bite, determine vaccination status of animal from owner
• Assess rabies risk & need for HRIG & HDCV (table below)
• HRIG: 20 IU/kg; 1/2 dose at exposure site, 1/2 dose IM in deltoid
• HDCV: 1 mL dose in deltoid in ED. F/u doses given days 3, 7, 14.
• HDCV 5th dose on day 28 if immunocompromised
• Do not stop rabies immunization b/c of mild rxn to vaccine doses
• Pre-exposure prophylaxis for at-risk individuals
• Rabies cases from nonbite exposures > from known bite exposures; consider prophylaxis for any contact w/ high-risk animals (esp bats)
Disposition
• D/c w/ return instructions, vaccination schedule
