japanese%20encephalitis%20virus
JAPANESE ENCEPHALITIS VIRUS

Japanese encephalitis virus is an RNA flavivirus that causes virus encephalitis across Asia, the western Pacific region and parts of Australia.

It is transmitted in an enzootic cycle and the virus is transmitted to humans through the bite of infected Culex tritaeniorhynchus mosquitoes.

There is no specific antiviral treatment for Japanese encephalitis virus and management is mainly symptomatic treatment and supportive care.

Personal protection from mosquito bites in endemic areas and obtaining vaccination are the primary strategies to control Japanese encephalitis virus infection due to lack of specific antiviral therapy, high case fatality, and substantial morbidity.

Diagnosis

  • Japanese encephalitis virus infection should be considered in a patient with evidence of a neurologic infection who has recently traveled to or resided in an endemic country in Asia or the western Pacific

Evaluation

Clinical and Laboratory Evaluation

Clinical Findings

  • Aside from the initial signs and symptoms mentioned, classic description of Japanese encephalitis virus infection includes a Parkinsonian syndrome with masklike facies, tremor, cogwheel rigidity and choreoathetoid movements
  • Seizures are usually generalized tonic-clonic that are common among children
    • Subtle focal seizures, such as twitching of an eyebrow or finger, can be important clinical findings

Laboratory Tests

Diagnostic Studies

  • Diagnosis of Japanese encephalitis virus infection is confirmed by detection of Japanese encephalitis virus-specific immunoglobulin M (IgM) antibodies in cerebrospinal fluid (CSF) or serum by enzyme-linked immunoabsorbent assay (ELISA)
    • Presence of Japanese encephalitis virus IgM in cerebrospinal fluid confirms infection of the central nervous system and can help distinguish clinical disease attributed to Japanese encephalitis virus from previous vaccination
    • While presence of Japanese encephalitis virus IgM in serum indicates recent Japanese encephalitis virus vaccination or asymptomatic infection
  • Japanese encephalitis virus-specific IgM antibodies are usually detectable 3-8 days after onset of illness and persists for 30-90 days, but longer persistence has been documented
    • Japanese encephalitis virus-specific IgM antibodies can be measured in the CSF of most patients by 4 days after onset of symptoms and in serum by 7 days after onset
  • To measure virus-specific neutralizing antibodies, plaque reduction neutralization tests (PRNT) can be performed
  • Vaccination history, date of onset of symptoms and information regarding other arboviruses known to circulate in the geographic area that might cross-react in serologic assays should be considered when interpreting results

Laboratory Findings

  • May include moderate leukocytosis, mild anemia and hyponatremia due to inappropriate antidiuretic hormone secretion
  • Thrombocytopenia and elevated hepatic enzymes have been noted
  • Cerebrospinal fluid opening pressure is elevated and has mild to moderate pleocytosis with lymphatic predominance, slightly elevated protein and normal ratio of cerebrospinal fluid to plasma glucose

Imaging

Imaging Studies

  • Magnetic resonace imaging of the brain most commonly shows thalamic lesions
    • Not a very sensitive marker for Japanese encephalitis virus but these can be highly specific for Japanese encephalitis virus in the appropriate clinical context
  • EEG abnormalities may include theta and delta coma, burst suppression, epileptiform activity and occasionally alpha coma
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