RATIONALE FOR SURVEILLANCE

Over a large part of East Asia, the Japanese encephalitis (JE) virus is the most common cause of encephalitis. This mosquito-borne encephalitis has a potential for outbreaks and can be associated with a high case-fatality rate. Three strategies for control based on the natural transmission cycle of Japanese encephalitis have been proposed:

 

• vector control
• vaccination of swine (virus-amplifying host associated with human epidemic disease)
• vaccination of humans

Surveillance should target these elements.

RECOMMENDED CASE DEFINITION

Clinical description

Japanese encephalitis virus infection may result in a febrile illness of variable severity associated with neurological symptoms ranging from headache to meningitis or encephalitis. Symptoms can include: headache, fever, meningeal signs, stupor, disorientation, coma, tremors, paresis (generalized), hypertonia, loss of coordination. The encephalitis cannot be distinguished clinically from other central nervous system infections.

Laboratory criteria for diagnosis

Presumptive:

Detection of an acute phase anti-viral antibody response through one of the following:

 

• Elevated and stable serum antibody titres to JE virus through ELISA, haemagglutination-inhibition or virus neutalization assays or

• IgM antibody to the virus in the serum

Confirmatory:

 

• Detection of the JE virus, antigen or genome in tissue, blood or other body fluid by immunochemistry or immunofluorescence or PCR, or

• JE virus-specific IgM in the CSF, or

• Fourfold or greater rise in JE virus-specific antibody in paired sera (acute and convalescent phases) through IgM/IgG, ELISA, haemagglutination inhibition test or virus neutalization test, in a patient with no history of recent yellow fever vaccination and where cross-reactions to other flaviviruses have been excluded

 

Note: JE infections are common and the majority are asymptomatic. JE infections may occur concurrently with other infections causing central nervous system symptoms, and serological evidence of recent JE viral infection may not be correct in indicating JE to be the cause of the illness.

Case classification

 

Suspected: A case that is compatible with the clinical description.
Probable: A suspected case with presumptive laboratory results.
Confirmed: A suspected case with confirmatory laboratory results.

RECOMMENDED TYPES OF SURVEILLANCE

Areas where no Japanese encephalitis transmission has been detected but where the vector is present:

 

Surveillance for acute central nervous system syndromes; investigation of clusters with fever.

Areas where disease is endemic with seasonal variation in transmission, and areas where epidemic Japanese encephalitis is occurring:

 

Routine weekly/monthly reporting of aggregated data on suspected, probable and confirmed cases from peripheral to intermediate and central level.

RECOMMENDED MINIMUM DATA ELEMENTS

Case-based data at the peripheral level

 

• Case classification (suspected/probable/confirmed)
• Unique identifier name of patient, age, sex, geographical information
• Date of onset
• Travel history over the past 2 weeks
• Hospitalization (Y/N)
• Outcome

Aggregated data for reporting

 

• Number of cases by age group
• Number of suspected/confirmed cases
• Number of hospitalizations and deaths

RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS

Number of cases and deaths by geographic area. Number of hospitalizations. Case-fatality rate.

PRINCIPAL USES OF DATA FOR DECISION-MAKING

 

• Target high risk areas for intervention
• Monitor changes in epidemiology and pattern of disease
• Monitor trends in endemic disease or re-emergence of disease
• Monitor vaccine efficacy

SPECIAL ASPECTS

Epidemic transmission in temperate zones is seasonal (summer of monsoon season months).

CONTACT

Regional Offices

See Regional Communicable Disease contacts on section "Communicable disease contacts in Regional Offices".

Headquarters: 20 Avenue Appia, CH-1211 Geneva 27, Switzerland

Communicable Diseases Surveillance and Response (CSR)

 

E-mail: arthurr@who.ch / outbreak@who.ch
Tel: (41 22) 791 2658/2636/2111
Fax: (41 22) 791 48 78