Rabies is a fatal viral zoonosis that causes 750,000 deaths worldwide each year.
Epidemiology
- Incidence – <100 cases each year in the U.S.; disease is endemic in Africa and Asia
- >55,000 cases each year worldwide (WHO 2002)
- Transmission – saliva from the bite of an infected animal; recently, transmission via tissue/organ transplantation; on rare occasions, transmission via aerosol droplets (lab accidents)
- In the U.S., the most commonly infected animals are bats, raccoons, skunks and foxes
- Infection by native dogs is uncommon in the U.S.
- Worldwide infections – 54% from dogs, 42% from wildlife, 4% from bats
Organism
- Single-stranded RNA virus
- Member of the Rhabdoviridae family
- Virus has predilection for nerve tissue, muscles and salivary glands
- Virus spreads via peripheral nerves to the brain, causing encephalomyelitis
Clinical Presentation
- Three phases of disease – prodromal, furious, paralytic
- Incubation period – 2 weeks to 6 years (average is 2-3 months)
- Prodromal phase
- Loss of appetite, headache, myalgias
- Furious phase (anterior horn cell dysfunction)
- Fever, insomnia, photophobia, dysarthria, difficulty swallowing, hydrophobia
- Paralytic phase (peripheral nerve dysfunction)
- Flaccid, ascending paralysis
- No hydrophobia
- Death within 5 days at this stage if ICU support not available
Treatment
- Clean wound
- Rabies vaccine (days 0, 3, 7, 14, 28 in deltoid only) plus rabies immunoglobulin infiltrated around wound at a dose of 20 IU/kg in a previously unvaccinated patient
- If not given the first day of exposure, immunoglobulin can be infiltrated up to 7 days after first vaccine dose
- Rabies vaccine (days 0 and 3) in a previously vaccinated patient
- Once the patient is symptomatic, vaccination does not improve prognosis and treatment is symptomatic
- <10 cases of survival from symptomatic rabies reported in the literature
- Two most recent survivors demonstrated high serum and CSF neutralizing antibody titers shortly after hospital admission without virus isolation
- Suggests that patients were able to produce antibodies against rabies virus
Prevention
- Rabies cannot be treated; therefore, prevention is essential
- Immunization of pets
- Pre-exposure prophylaxis in high-risk populations (veterinarians, animal handlers, lab personnel who handle the virus)
- Rabies vaccine – should have IgG testing to evaluate immunization status with repeat every 6 months if in high-exposure job
- Immediate post-exposure prophylaxis
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