Infectious period: Humans are incidental or dead-end hosts as they do not develop high enough concentrations of JE virus in their bloodstream to infect feeding mosquitoes.

Clinical features

Most human infections are asymptomatic.
Relatively mild forms of the disease occur as aseptic meningitis or a non-specific febrile illness. Less than 1% will develop encephalitis.
In those who develop encephalitis, illness begins with a non-specific febrile prodrome of headache, abdominal pain, nausea and vomiting for several days. This is followed by altered mental state, drowsiness, and coma.
Convulsions are common in the paediatric population.
Some develop a Parkinsonian syndrome.
Sequelae include parkinsonism, paralysis, seizures, mental retardation, and psychiatric complaints in up to 70% of survivors.

Risk factors

Risk factors include:

Living in or travelling to JE affected areas

Diagnosis

Japanese encephalitis can be diagnosed by:

Detection of virus-specific antibody in CSF or serum.
Detection of virus-specific antigens in tissue.
Isolation of virus in serum, plasma, blood, CSF or tissue; or polymerase chain reaction (PCR) (Note: short period of viremia limits the usefulness of PCR).

Treatment and management

There is no specific antiviral treatment available. Treatment is supportive and anticonvulsants are used to control seizures.

Precaution, prevention, and control

Standard precautions apply in healthcare settings.

Vaccination is available. The vaccine is recommended for persons travelling to endemic regions for more than 1 month and are staying or working in rural areas.

Travellers who are at risk should take mosquito precautions in addition to vaccination.

Vector control remains the mainstay in reducing the spread of mosquito-borne diseases. Individuals can also take precautions against mosquito bites, such as:

Staying in rooms which are well-screened or air-conditioned.
Wearing long, covered clothing that cover most of your body.
Applying an effective insect repellent, such as those containing DEET, Picaridin or IR3535 as the active ingredient regularly.

Notification

Who should notify:

Medical practitioners
Laboratories

When to notify:

On clinical suspicion or laboratory confirmation

How to notify:

Please refer to the Infectious Disease Notification for more information.

Notification timeline:

As soon as possible. No later than 24 hours from the time of diagnosis.

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the number of confirmed Japanese encephalitis cases in Singapore.