Japanese Encephalitis
Queensland Health Guidelines for Public Health Units
Revision History
| Version | Date | Changes |
|---|---|---|
| 1.0 | March 2010 | Full revision of guideline |
| 1.1 | April 2011 | Change to Notification Criteria and Notification Procedure |
| 2.0 | March 2023 | Full revision of guideline |
Infectious agent
The infectious agent is the Japanese encephalitis virus (JEV), a mosquito-borne flavivirus.
Notification criteria
In March 2022 JEV was declared a Communicable Disease Incident of National Significance (Australian Government Department of Health and Aged Care, 2023). The national surveillance case definition was revised by the Communicable Diseases Network Australia (CDNA) and implemented in January 2023 and retrospectively applied from January 2021 (CDNA, 2023).
Reporting
Only confirmed cases and probable cases should be notified.
Confirmed case
A confirmed case requires laboratory definitive evidence[1]from a laboratory with extensive experience in the diagnostic testing of arbovirus.
Laboratory definitive evidence
1. Isolation of JEV by culture.
or
2. Detection by nucleic acid testing (NAT) specific for JEV.
or
3. lgG seroconversion or a diagnostically significant increase in antibody level or a fourfold or greater rise in JEV-specific IgG titres proven by neutralisation or another specific test, with no history of recent vaccination against JEV.[2]
or
4. Detection of JEV-specific IgM in cerebrospinal fluid (CSF), without the detection of other flavivirus-specific IgM.[3]
2 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.
3 E.g. Murray Valley encephalitis, West Nile/Kunjin, and/or dengue virus.
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 suggestive evidence
1. Detection of JEV-specific IgM in CSF which is significantly greater than other flavivirus-specific IgM levels, (if also detected).[4]
or
2. Detection of JEV-specific IgM in serum with no history of recent JEV vaccination.[5]
(a) without detection of other flavivirus-specific IgM in serum or CSF.
or
(b) which is significantly greater[6] than other flavivirus-specific IgM levels (if also detected).
or
3. Detection of JEV-specific IgG in CSF:
(a) without detection of other flavivirus-specific IgG.
or
(b) which is significantly greater than other flavivirus-specific IgG levels (if also detected).
and
(c) with no history of recent JEV vaccination unless the case also has encephalitic illness compatible with JEV infection in the absence of a known alternative cause.[7]
4 E.g. Murray Valley encephalitis, West Nile/Kunjin, and/or dengue virus.
5 Recent vaccination is considered 28 days; however, advice should be sought from the authorising pathologist and the clinician regarding individual circumstances. Convalescent serum should be collected where possible.
6 Public health units should seek advice from the responsible authorising pathologist with regard to the interpretation of JEV positive serology results in the presence of other flaviviruses.
7 Including but not limited to other flaviviruses (such as Murray Valley encephalitis, West Nile/Kunjin, and dengue viruses), herpes simplex virus, varicella zoster virus, and enteroviruses.
Clinical evidence[8]
1. 1. Encephalitic disease: acute febrile meningoencephalitis characterised by one or more of the following:
- focal neurological disease, or seizures, or acute impairment in level of consciousness
- an abnormal computerised tomogram (CT) or magnetic resonance image (MRI) or electroencephalogram (EEG) consistent with flavivirus encephalitis
- presence of pleocytosis in CSF.[9]
or
2. 2. Non-encephalitic illness: acute febrile illness with headache, with or without myalgia or rash.
8 While clinical evidence is required for classification/reporting purposes, JE is not clinically notifiable under the Public Health Act 2005.
9 Not definitive, but ≥5 leucocytes/μl is indicative.
Disease cluster criteria
More than one case of locally acquired (symptomatic) JEV within a group of people with geographical similarities in a specific time period.
Notification procedure
JEV is notifiable on pathology request or pathological diagnosis.
Reporting to NOCS
Both confirmed and probable cases should be reported.
Objectives of surveillance
To identify cases, disease clusters and state trends so that appropriate public health action can be taken.
To contribute to integrated one health surveillance for risk mapping and modelling of JEV distribution in Queensland and nationally to inform policy development, resource allocation and impact of disease control programs.
To meet national reporting requirements.
Public health significance and occurrence
JEV is a mosquito-borne flavivirus that is the leading cause of childhood encephalitis in Asia. The virus is widely distributed in southeast and southern Asia extending from western China and India east to Japan and south into Indonesia, Papua New Guinea and Australia. There are an estimated 68,000 cases and between 14,000 and 21,000 deaths reported annually worldwide, although this is likely an underestimate.
Prior to 2021, locally acquired human infection with JEV had only been reported in the north of Australia (Cape York and the Torres Strait Islands) with a total of 5 cases and 2 deaths reported during outbreaks in 1995 and 1998. JEV activity, as demonstrated by mosquito and/or sentinel pig surveillance, was reported almost annually between 1995 and 2005, the year surveillance was discontinued in the Torres Strait.
In early 2021, JEV was diagnosed in a resident of the Tiwi Islands off the coast of the Northern Territory. Since the end of February 2022, there have been detections of JEV in commercially produced pigs, mosquitoes, wild pigs and humans across several Australian states and territories. This represents the first record of virus activity over a large geographical area of the Australian mainland. On 4 March 2022, Australia’s Acting Chief Medical Officer declared the JEV situation a Communicable Disease Incident of National Significance. Between 1 January 2021 and 5 January 2023, there have been 45 human cases of JEV notified in Australia (35 confirmed and 10 probable) (Australian Government Department of Health and Aged Care, 2023). Queensland reported 5 JEV cases during that same period (2 confirmed and 3 probable). Nationally, 7 people have died, including one person from Queensland, during this period. Although suitable ecological conditions exist for JEV to become established in Australia, there is uncertainty regarding when and where ongoing transmission will occur.
Clinical features
Most JEV infections in humans are asymptomatic with less than one per cent of infections resulting in clinical disease. JEV typically has a prodromal phase characterised by fever, headache and gastrointestinal symptoms which can rapidly progress to a reduced level of consciousness and coma. Seizures may occur. On rare occasions, JEV can also present as acute flaccid paralysis, similar to that seen in poliomyelitis. The encephalitis cannot be distinguished clinically from other central nervous system infections. In encephalitic cases, there is a case fatality rate of between 20 and 30 per cent. Permanent neurologic or psychiatric sequelae can occur in 30 to 50 per cent of patients with encephalitis (World Health Organization, 2019).
Reservoir
The primary amplifying hosts of JEV in endemic areas of Asia are wild-wading birds (like herons and egrets) and pigs. In many areas, pigs are considered important in epidemic transmission of the virus that leads to spillover to humans.
Other vertebrate species can be infected but do not always exhibit disease such as horses, cattle, buffalo, dogs, sheep, alpacas and goats, as well as humans. These species do not appear to be amplifying hosts of JEV because they usually do not produce virus levels sufficient to infect mosquitoes.
Mode of transmission
JEV is a zoonotic virus transmitted between amplifying hosts (water birds and pigs) and humans by mosquitoes. Across its distribution, JEV has been isolated from a wide range of mosquito species, but Culex mosquitoes are considered the primary vectors.
In Australia, Culex annulirostris was shown to be the main vector for both human and zoonotic JEV transmission in the 1990s. This species has a wide geographical distribution, utilises groundwater habitats for larval development, readily feeds on hosts of the virus and humans, and can have large populations following flood events. Other species, like Culex gelidus, Culex sitiens and Culex quinquefasciatus may play a role in transmission in some areas, but further investigation of their vector status is required.
Humans are not efficient amplifying hosts and therefore are ‘dead-end’ hosts in the JEV transmission cycle. Humans only become infected through the bite of an infected mosquito. JEV cannot be transmitted directly from person-to-person or from infected animals to people. There is no risk of infection from consuming pork or pork products.
Incubation period
Usually 5–15 days.
Period of communicability
Not applicable - direct person-to-person spread of JEV does not occur.
Susceptibility and resistance
Susceptibility to clinical disease is usually highest in infancy and old age; inapparent or undiagnosed infection is more common at other ages. Infection confers life-long immunity.
Testing advice in Queensland
The following advice is in addition to usual investigations for encephalitis/viral meningoencephalitis including herpes simplex virus (HSV), enterovirus and varicella zoster virus (VZV) PCR on CSF and serology.
For both adults and children, the following samples should be collected:
1. Blood (serum tube – 2–5mls for children, 5–8mls for adults)
- acute period: flavivirus antibodies (suspected JEV, acute phase') AND JEV PC
- convalescent period (3–4 weeks post-onset): flavivirus antibodies ('suspected JEV, convalescent phase')
- to assist with results interpretation, please indicate on request forms for serology:
- vaccination status for JEV/yellow fever,
- past flavivirus infection (e.g. dengue), and
- any autoimmune disease.
2. Where a lumber pucture procedure is in scope, collect CSF (at least 1ml)
- flavivirus lgM ('suspected JEV')
- JEV PCR.
Specimens should be stored at 4o C and transported as soon as possible.
Management
Cases
Investigation
Determine whether the case acquired JEV locally or overseas.
Management
If considered to be locally acquired, refer to the locally acquired cases/disease clusters section below.
Contacts
Contact Tracing
Not routinely required. If the case is considered to be locally acquired, refer to the locally acquired cases/disease clusters section below.
Locally acquired cases/disease clusters
The response to a locally acquired JEV case or disease cluster requires a collaborative One Health approach between essential stakeholders responsible for human and animal health. Stakeholders may include specialists in human and animal disease control, epidemiologists, medical entomologists, vector control personnel, environmental health officers, workplace health and safety officers, representatives from the animal production industry, primary health care, laboratory and communications personnel). In certain contexts, a multiagency incident management framework may be considered to streamline stakeholder interactions and communication flows.
Humans
When responding to JEV, the following factors should be considered:
- assessment of the case’s possible location/s of exposure during the likely exposure period. This assessment includes consideration of places where the case stayed overnight or engaged in evening/overnight outdoor activities (e.g. camping), proximity to water sources or amplifying animal hosts, recall of the presence of significant numbers of mosquitoes, mosquito precautions used etc
- prompt notification to local health care providers (GPs, community health centres, hospitals) of the cases/clusters with request to be vigilant for further case presentations
- implementation of a communication strategy to inform the local community of a locally acquired JEV case or disease cluster and any recommended measures to minimise risk of infection. Local media, informed by public health advice, should be considered to ensure culturally appropriate information is disseminated within local communities
- it is crucial that mosquito control and bite avoidance measures are implemented immediately in the communities and households in the vicinity of the JEV detections
- a serosurvey may be considered under some conditions, to identify asymptomatic or mild (non-encephalitic) human infections and to understand disease burden.
Mosquito vectors
The response to a disease cluster of JEV should involve mosquito surveillance and control, and should align with the Interim Queensland Japanese Encephalitis Virus Mosquito Surveillance and Control Plan.
Surveillance activities should include collection of adult mosquitoes using CO2-baited light traps and an environmental survey of all groundwater and container water sources to identify productive larval habitats that may need to be targeted for control. A medical entomologist can advise on the types of likely productive larval sites in the locality where the infection may have been acquired.
An integrated approach involving a combination of environmental, larval and adult control methods is recommended for the control of mosquitoes involved in JEV transmission. However, there are numerous constraints to effective mosquito control in response to JEV which include, but are not limited to, the large geographical area that is utilised by vectors as larval habitats and the potential for long-distance dispersal of adult mosquitoes from these locations. Irrespective of the approach to control used, it is important that potential effects on non-target species are minimised and that there is adequate communication to inform the community and stakeholders of intended control activities.
Animal hosts
A One Health approach to managing JEV detections is recommended for surveillance and control activities, with collaborative approaches tailored to the scenario. Engagement should occur with representatives from animal health authorities, industry, landowners, workplace health and safety authorities, and research partners, using existing mechanisms for communication and information sharing.
While it is not possible to eradicate mosquitoes, there are measures available to piggery owners, and people with pet pigs or smaller herds to manage mosquito production on their properties. People working with pigs, including those who may have a small herd or pet, should take steps to control mosquitoes, and continue to use effective biosecurity measures.
Activities that may be considered include:
- identifying the location of any domestic or wild pigs near likely exposure sites
- where pigs are kept within communities (i.e., pigs kept in a backyard setting, or small-scale non-commercial breeding operation), assessment of the feasibility of relocating pigs away from immediate proximity to residences
- serosurveys including domestic pigs and feral pigs, to ascertain the geographic extent of porcine infection
- identification and mapping of wading bird populations near likely exposure sites
- mosquito surveillance near likely exposure sites.
Preventative measures
A One Health approach to managing JEV detections is recommended for surveillance and control activities, with collaborative approaches tailored to the scenario. Engagement should occur with representatives from animal health authorities, industry, landowners, workplace health and safety authorities, and research partners, using existing mechanisms for communication and information sharing.
While it is not possible to eradicate mosquitoes, there are measures available to piggery owners, and people with pet pigs or smaller herds to manage mosquito production on their properties. People working with pigs, including those who may have a small herd or pet, should take steps to control mosquitoes, and continue to use effective biosecurity measures.
Activities that may be considered include:
- identifying the location of any domestic or wild pigs near likely exposure sites
- where pigs are kept within communities (i.e., pigs kept in a backyard setting or small-scale non-commercial breeding operation), and assessment of the feasibility of relocating pigs away from immediate proximity to residences.
- serosurveys including domestic pigs and feral pigs, to ascertain the geographic extent of porcine infection.
- identification and mapping of wading bird populations near likely exposure sites.
- mosquito surveillance near likely exposure sites.
JE Vaccine
Recommendations for the use of JEV vaccines are detailed in the Australian Immunisation Handbook and in the Australian Technical Advisory Group on Immunisation (ATAGI) clinical guidance. There are currently 2 JEV vaccines registered for use in Australia:
- Imojev (Sanofi Pasteur) is a single-dose, live attenuated virus vaccine (which is not suitable for some people, such as pregnant women and those who are immunocompromised) and is registered for use in people ≥ 9 months of age, and
- JEspect (Seqirus)[10], an inactivated vaccine given as a two-dose schedule a minimum of 28 days apart (or 7 days apart in adults if they are at risk of immediate exposure to the virus) and is registered for use from ≥ 2 months of age. Pregnant women and people who are immunocompromised can receive this vaccine.
Booster doses are recommended for certain individuals if there is an ongoing risk to JEV infection (Australian Government Department of Health and Aged Care, 2022). The need for a booster dose of JEV vaccine depends on the time elapsed since primary vaccination, and the vaccine type used for this primary course. Details on booster doses are included in the ATAGI clinical guidance.
Both JEspect and Imojev were made using the SA14-14-2 virus strain. Vaccines based on this virus strain have been shown to provide protection against the different virus genotypes (1, 2 and 4) that have occurred in Australia.
In the event of a human case or detection of the virus in local mosquitoes, birds, pigs or other animals, a risk assessment should be undertaken to determine whether a targeted vaccination program is required.
The risk groups that are currently eligible for publicly funded vaccines in QLD can be found on the Japanese Encephalitis Fact sheet
A full list of JEV vaccine service providers can be found on the QH Immunisation clinic finder map
JEV vaccination is also recommended for travellers to, and expatriates residing in, endemic and epidemic countries. Risk is dependent on season and duration of travel, regions visited, and extent of outdoor activity and use of mosquito avoidance measures. See current edition of Australian Immunisation Handbook for recommendations for travellers.
10 Note: JESpect is also known as Ixlaro in some other countries (manufactured by Valneva and distributed in Australia by Seqirus/CSL).
Personal protective measures to limit exposure to mosquito bites
Educating the public and those with high-risk exposure about personal protection against mosquitoes is a critical strategy to help reduce human transmission risks. These protective measures include:
- wearing of long-sleeved loose-fitting clothing and enclosed footwear
- application of repellents containing DEET, picaridin or oil of lemon eucalyptus, applied at regular intervals in accordance with label directions
- using insecticide sprays, vapour dispensing units (indoors) and mosquito coils (outdoors)
- wearing of long-sleeved loose-fitting clothing and enclosed footwear
- application of repellents containing DEET, picaridin or oil of lemon eucalyptus, applied at regular intervals in accordance with label directions
- using insecticide sprays, vapour dispensing units (indoors) and mosquito coils (outdoors)
- avoiding areas of high mosquito activity at dawn and dusk
- ensuring insect screens in dwellings, caravans and tents are functional.
Resources
Australian Government Department of Health and Aged Care 2022, ‘Australian Immunisation Handbook, Japanese Encephalitis’ retrieved 6 February 2023
Australian Government Department of Health and Aged Care 2022 ‘The Australian Technical Advisory Group on Immunisation (ATAGI) clinical guidance on Japanese encephalitis virus vaccines’ retrieved 6 February 2023
Hills, S, Fischer, D, Heymann, MD 2016 ‘Japanese Encephalitis, Control of Communicable Diseases Manual’ retrieved 6 February 2023
Moore, S 2021, ‘PLOS neglected tropical diseases, the current burden of Japanese encephalitis and the estimated impacts of vaccination: Combining estimates of the spatial distribution and transmission intensity of a zoonotic pathogen’ retrieved 6 February 2023
Quan, TM, Thao, TTN, Duy, NM, Nhat, TM, Clapham, H 2020, ‘Estimates of the global burden of Japanese encephalitis and the impact of vaccination from 2000-2015’ retrieved on 6 February 2023
Queensland Government 2023 ‘Japanese encephalitis’ retrieved 6 February 2023
Queensland Health 2022, ‘Communicable disease control guidance, Japanese encephalitis’ retrieved 6 February 2023
Queensland Health 2022 ‘Interim Queensland Japanese encephalitis virus mosquito surveillance and control plan, retrieved 6 February 2023
Queensland Health 2023 ‘Japanese encephalitis virus (JEV) vaccination centres’ retrieved 6 February 2023
The National Vector Management Group 2022 (Animal Health Australia and Plant Health Australia Limited) ‘Integrated Mosquito Management Principles for Piggeries’ retrieved 6 February 2023
References
Australian Government Department of Health and Aged Care 2023, ‘Japanese encephalitis virus (JEV)’ retrieved 2 February 2023
Australian Government Department of Health and Aged Care 2022, ‘Japanese encephalitis virus (JEV) vaccines’ retrieved 3 February 2023,
Communicable Diseases Network Australia 2023, ‘Japanese encephalitis virus Infection Australian national notifiable diseases case definition’ retrieved 2 February 2023
World Health Organization 2019, ‘Japanese Encephalitis’ retrieved 2 February 2023