Japanese Encephalitis Clinical Presentation

Updated: Apr 06, 2023
  • Author: Antonette B Climaco, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Individuals with Japanese encephalitis virus (JEV) infection have a history of mosquito exposure in an endemic area. Most infections in humans are asymptomatic. Less than 1% of people infected with Japanese encephalitis virus develop symptomatic disease. Severe disease is estimated to occur at 1 per 250 Japanese encephalitis virus infections. Symptomatic Japanese encephalitis virus infection can present as a nonspecific febrile illness, aseptic meningitis, or encephalitis. The incubation period averages 6-8 days, with a range of 5-15 days. The prodromal period is characterized by fever, headache, nausea, diarrhea, vomiting, and myalgia, which may last for several days.

Altered mental status may rapidly follow and can range from mild confusion to agitation to overt coma. Seizures develop more often in children, whereas headache and meningismus are more common in adults. Acute encephalitis is the most common neurologic manifestation.

Mutism has been reported as a presenting symptom. Acute flaccid paralysis also has been described, attributed to the involvement of anterior horn cells resulting in a poliomyelitis-like presentation. Fevers disappear by the second week, and parkinsonian features (choreoathetoid movement, tremor, dystonia) develop as the other neurologic symptoms disappear.


Physical Examination

Neurologic signs of Japanese encephalitis vary.

Generalized weakness, hypertonia, and hyperreflexia (including the presence of pathologic reflexes) are common.

Papilledema develops in less than 10% of patients, and 33% have cranial nerve findings (eg, disconjugate gaze, cranial nerve palsies).

Parkinson-like extrapyramidal signs are common, including masklike facies, tremor, rigidity, and choreoathetoid movements.

In one study, central hyperpneic breathing and extrapyramidal signs were the best clinical predictors of infection (41% sensitive, 81% specific). [21]

Patients may present with acute-onset symmetric paralysis, which may be concerning for Guillain-Barré syndrome. [22]



Coinfection of Japanese encephalitis virus and neurocysticercosis may result from the role of pigs in the life cycle of both viruses. [23, 24]

An unusual association between Japanese encephalitis virus and acute obstructive hydrocephalus has been described. [25]

A possible case of acute disseminated encephalomyelitis [26] and a case of acute transverse myelitis [27] have been described.

Bacterial infections (eg, pneumonia, urinary tract infection) related to the supportive care of patients with Japanese encephalitis virus are the most common complications.

Individuals from tropical areas where Japanese encephalitis virus is endemic also are at risk for infection with other tropical diseases (eg, malaria, typhoid fever, other parasitic infections).