Rabies Virus

Diagnosis

Indications for Testing

  • Symptoms compatible with disease and no other known etiology; history of animal bite that was not treated with rabies immunoglobulin

Laboratory Testing

  • Rabies diagnosis information (CDC)
  • Disease is frequently not recognized until after death
  • Antemortem – CSF, salivary or virus-specific fluorescent material in skin biopsies taken from the nape of the neck; recent polymerase chain reaction (PCR) using saliva, tears and skin biopsy
  • Postmortem – presence of Negri bodies by direct visualization or direct immunofluorescence on brain biopsy; antibody testing of the brain

Histology

  • Antemortem – corneal impression for the presence of viral antigens

Differential Diagnosis

Clinical Background

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

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Rabies Antibody, IgG (Vaccine Response) 0099132
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Assess the degree of immunization following vaccination

Intended for vaccine response only, not for diagnosis of infection