1. Reason for surveillance
2. Case definition
3. Notification criteria and procedure
4. The disease
5. Managing single notifications
6. Additional resources

1. Reason for surveillance

1. To identify, investigate and manage cases of the disease
2. To monitor the epidemiology and so inform the development of better prevention and control strategies amongst the NSW population including vaccination of people at risk.

2. Case definitions

Prior to the 2021/22 mosquito season, Japanese encephalitis had only been diagnosed in residents who had travelled overseas except for sporadic cases of locally acquired JEV identified in the Torres Strait and Cape York Peninsula. Considering the recent outbreak of JE cases in NSW, the surveillance case definition has been updated to better reflect the evolving changes.

Confirmed case

A confirmed case requires laboratory definitive evidence* from a laboratory with extensive experience in the diagnostic testing of arbovirus.

*Non-encephalitic cases detected as part of a serosurvey should not be notified

Probable case

A probable case requires laboratory suggestive evidence from a laboratory with extensive experience in the diagnostic testing of arbovirus AND clinical evidence.

Laboratory definitive evidence

1. Isolation of Japanese encephalitis virus (JEV) by culture or
2. Detection by nucleic acid testing (NAT) specific for JEV or
3. IgG seroconversion or a diagnostically significant increase in antibody level or a fourfold or greater rise in JEV-specific titres IgG proven by neutralisation or another specific test, with no history of vaccination against JEVⁱor
4. Detection of JEV-specific IgM in cerebrospinal fluid (CSF), without the detection of other flavivirus-specific IgMⁱⁱ

Laboratory suggestive evidence

1. Detection of JEV-specific IgM in CSF which is significantly greaterⁱⁱⁱ than other flavivirus-specific IgM levels (if also detected)ⁱⁱ or
2. Detection of JEV-specific IgM in serum with no history of recent JEV vaccinationⁱ
1. without detection of other flaviviruses-specific IgMⁱⁱ or
2. which is significantly greaterⁱⁱⁱ than other flavivirus-specific IgM levels (if also detected)ⁱⁱ or
3. Detection of JEV-specific IgG in serum or CSF:
1. without detection of other flavivirus-specific IgG or
2. which is significantly greaterⁱⁱⁱ than other flavivirus-specific IgG levels (if also detected) AND
3. in the absence of JEV vaccination unless the case also has encephalitic illness compatible with JEV infectionin the absence of a known alternative cause ^iv

Clinical evidence

1. Encephalitic disease: acute meningoencephalitis characterised by one or more of the following:
1. focal neurological disease, or seizures, or acute impairment in level of consciousness;
2. an abnormal computerised tomogram (CT) or magnetic resonance image (MRI) or electroencephalogram (EEG) consistent with flavivirus encephalitis;
3. presence of pleocytosis in cerebrospinal fluid or
2. Non-encephalitic illness: acute febrile illness with headache, with or without myalgia or rash.
1. Recent vaccination is considered to be 28 days, however advice should be sought from the authorising pathologist and the clinician regarding individual circumstances. Convalescent serum should be collected where possible.
2. E.g. Murray Valley encephalitis, West Nile/Kunjin and/or dengue virus.
3. Public health units should seek advice from the responsible authorising pathologist with regard to the interpretation of JEV positive serology results in the presence other flaviviruses.
4. Including but not limited to other flaviviruses (such as Murray Valley encephalitis virus, West Nile/Kunjin and dengue viruses), Herpes Simplex Virus, Varicella Zoster Virus and enteroviruses.
5. Not definitive, but ≥ 5 leucocytes/ μl is indicative.

3. Notification criteria and procedure

Japanese encephalitis (JE) cases are to be notified by laboratories on diagnosis (ideal reporting by telephone within 1 hour of diagnosis).

Both confirmed and probable cases should be entered onto NCIMS.

Patients with a clinically compatible syndrome suggestive of JE should be referred to hospital for further investigation and management.

4. The disease

Infectious agents

Japanese encephalitis is one of the arboviruses (arthropod borne viruses known to be pathogenic for humans). Japanese encephalitis virus (JEV) is a member of the genus Flavivirus, in the family Flaviviridae. Dengue, Murray Valley Encephalitis, Kunjin, Kokobera, Stratford, Alfuy, New Mapoon and Edge Hill are also flaviviruses.

Mode of transmission

JEV is transmitted by the bite of an infected mosquito, primarily Culex species which are commonly found in NSW and most active at dusk and dawn. The virus is maintained in a cycle between mosquitoes and amplifying vertebrate hosts, primarily pigs and wading birds.

Humans are incidental or dead-end hosts, because they usually do not develop a level or duration of viremia sufficient to infect mosquitoes. Humans cannot be infected by touching an infected animal or consuming animal products. There is no evidence for direct person-to-person spread.

Timeline

The incubation period ranges from 5 to 15 days.

Clinical manifestations

Less than 1% of people infected with JEV experience clinical disease. Symptoms may include fever, headache, myalgia, rash and diarrhoea.

Severe disease is associated with acute encephalitis/meningoencephalitis. Neurological sequelae include focal deficits such as paresis, cranial nerve pathology and movement disorders. Seizures are common, particularly in children. Rarely, there may be other presentations including acute flaccid paralysis and arthralgia.

Permanent neurological or psychiatric complications occur in 30-50% of cases with severe disease. The case fatality rate for those with severe disease can be as high as 30%.

The clinical presentation for JE can be similar to that of Murray Valley Encephalitis (MVE) and Kunjin virus.

Geographic distribution

JEV is endemic in much of Asia and parts of the Pacific. Prior to 2022, JE was normally only diagnosed in residents who had travelled overseas, however sporadic cases of locally acquired JEV had previously been identified in the Torres Strait and Cape York Peninsula. A map of the global distribution of the Japanese encephalitis virus is available but note this map exaggerates Australian distribution.

In late February 2022, JEV was confirmed in commercial pig farms in NSW, Queensland, Victoria and then South Australia. This is believed to be the first incursion of the virus into South-Eastern Australia. During this first season, 42 locally-acquired cases of JEV were identified, of which 13 were in NSW. Further information is available at Japanese encephalitis.

Testing advice in NSW

A clinically compatible case with a concern for acute JEV infection should have the following samples obtained by their treating clinician:

• Blood (serum) for acute testing for Flavivirus and JEV IgM, IgG and Total Antibody (Ab)
• Whole blood for JEV PCR +/- viral culture and
• Urine for Flavivirus IgM, IgG and Total Antibody (Ab), JEV PCR +/- viral culture and
• Cerebrospinal fluid (CSF) (where felt safe and appropriate to do so) for Flavivirus and JEV IgM, IgG and Total Ab, JEV PCR +/- viral culture.

Convalescent sampling may be sent 3-4 weeks after the acute event for diagnostic purposes to assess for acute seroconversion or a diagnostically significant rise in JEV antibody levels. This should be performed in consultation with an Infectious Diseases Physician and or Microbiology laboratory.

The Institute of Clinical Pathology and Medical Research (NSW Health Pathology – ICPMR) at Westmead Hospital is currently the only public NSW laboratory with extensive experience in the diagnostic testing of arboviral infection.

5. Managing single notifications

Response times

Investigation

On the same day of notification of a confirmed case begin a follow-up investigation and notify the One Health Branch (or for after-hours escalations, CD on call) of the case details.

Data entry

Within one working day of notification enter confirmed JE cases on NCIMS.

Response procedure

The response to a notification will normally be carried out in collaboration with the case's health carers. But regardless of who does the follow-up, PHU staff should ensure that action has been taken to:

• confirm the onset date and symptoms of the illness
• confirm results of relevant pathology tests, or recommend the tests be done (encourage the managing doctor to take convalescent sera to confirm the diagnosis, see 'testing advice in NSW' above)
• find out if the case or relevant care-giver has been told what the diagnosis is before interviewing them
• seek the doctor's permission to contact the case or relevant care-giver
• review case management
• identify the likely source of infection.

Case management

Clinicians in NSW should have a strong index of suspicion for Japanese encephalitis in clinically compatible cases, particularly in the areas of Murrumbidgee, Western and Far West Local Health Districts with previous JEV detections in mosquitos, sentinel chickens, animals or human exposures.

Treatment

Supportive treatment only.

Education

The case or relevant caregiver should be informed about the nature of the infection and the mode of transmission.

Exposure investigation

All cases (whether local or overseas acquired) should be asked to recall if, in the incubation period, they had:

• been bitten by mosquitoes or
• visited regions where JE is endemic or where there have been any confirmed detections of JEV in humans, mosquitoes or animals or
• participated in occupational, recreational, or any outdoor activity near potentially productive mosquito habitats, such as areas near rivers, ponds and marshes, including flood zones and wherever there are bodies of standing water or
• been in proximity to domestic or feral pigs in an occupational, residential or recreational setting.

For locally acquired cases, the National Outbreak Case Questionnaire should be completed for each JE case (confirmed or probable). The National Outbreak Case Questionnaire is available on the Infectious Diseases Network Sharepoint site under Vector-Borne Diseases > Japanese Encephalitis. Previous vaccination against JE (including date received) and or previously confirmed infection with JE, should also be documented.

Isolation and restriction

None.

Environmental evaluation

NSW Health is currently working to better understand the risk to humans in affected local areas in Australia. Where locally acquired cases are identified, work with your Environmental Health Officers to determine if there is surveillance in the area and/or whether another support for the management of mosquitos is required. Local councils may be asked to engage in vector control activities where large numbers of mosquitos are present or to promote mosquito warnings in areas of particularly high risk.

Contact management

Identification of contacts

Public health units should identify any potentially co-exposed contacts. Potentially exposed people are those who may have been exposed to the same source (if known) as the case (e.g. family members in the same household if case likely exposed at home). These individuals should be counselled on the signs and symptoms of JEV. They should be given advice on immunisation as prophylaxis, and education on mosquito bite prevention to help protect against JEV and other mosquito-borne illnesses.

Where the exposure location is in an area of NSW not previously identified as eligible for vaccination, seek urgent advice with the One Health Branch on vaccination for contacts and community.

Communication of further risk to public

As local transmission in NSW has only recently been identified, there remains significant public interest in understanding the geography of risk and alerting the public. It is highly likely that notification of JEV will prompt a media response, particularly when the event:

• represents the first detection of the season
• occurs in an area which has not had confirmed JEV previously
• is suggestive of transmission in an area outside the area of vaccine eligibility
• occurs in a person not eligible for vaccination
• affects a child or other vulnerable person
• is one of the multiple cases in the same area