- Japanese encephalitis (JE) is a rare but potentially serious infection of the central nervous system caused by the JE virus.
- Cases of JE have been reported in Victoria and other south-eastern Australian states this mosquito season. Cases were reported for the first time in Victoria in 2022.
- JE virus is transmitted to humans by infected mosquitoes.
- Most infections are asymptomatic, and less than one per cent of infected people develop clinical disease.
- Consider testing for JE and other mosquito-borne diseases in patients with a compatible illness.
- Treatment is supportive. The best prevention is to protect against mosquito bites.
- JE vaccine is available for specific groups at higher risk of exposure to the virus.
- JE is an ‘urgent’ notifiable condition. Suspected and confirmed cases must be notified immediately to the Department of Health by medical practitioners and pathology services.
Notification requirement for Japanese encephalitis
JE is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately to the Department of Health upon initial diagnosis (suspected or confirmed) by calling (24 hours). Pathology services must follow up with written notification within 5 days.
This is a Victorian statutory requirement.
Primary school and children’s services exclusion for Japanese encephalitis
Exclusion is not required.
Infectious agent of Japanese encephalitis
JE is caused by infection with the Japanese encephalitis virus which is a flavivirus.
Other flaviviruses known to cause similar clinical presentations include Murray Valley encephalitis virus and West Nile/Kunjin virus.
Identification of Japanese encephalitis
Most JE virus infections are asymptomatic. Less than one percent of people with JE virus infection develop clinical disease. While acute encephalitis is the most commonly recognised clinical manifestation of JE virus infection, milder forms of disease, such as aseptic meningitis or undifferentiated febrile illness, can also occur.
Mortality from encephalitis is 20 to 50%. Among survivors, 30 to 50% may have significant neurological complications.
Illness usually begins with:
People with severe illness can develop encephalitis or meningoencephalitis and have symptoms such as:
- drowsiness, confusion or other mental status changes
- meningism with severe headache, neck stiffness and photophobia
- cranial nerve pathology
- generalised weakness or paresis
- movement disorders such as ataxia and Parkinsonism
- seizures, which are more common in children
- loss of consciousness and coma
Confirmation of JE is made by isolating or detecting the virus from a clinical sample or by a rising antibody titre in conjunction with compatible clinical evidence.
Bilateral thalamic involvement on CT or MRI Brain is classical. Other areas that may be involved include the basal ganglia and brainstem.
The usual investigations for common causes of encephalitis or meningoencephalitis should be conducted concurrently, including CSF sampling if safe and appropriate. Where CSF is obtained, it should be tested for Herpes Simplex Virus (HSV), varicella-zoster virus (VZV), enteroviruses and other common causes of meningoencephalitis by multiplex PCR and culture.
Flavivirus testing should be considered in the appropriate clinical context. It is especially important to exclude bacterial meningitis and HSV as they are treatable conditions.
Recommended laboratory testing for JE includes all of the following:
Blood – serum(2 to 5mL in children, 5 to 10 mL in adults, in a serum tube)
Blood - whole blood(2 to 5mL in children, 5 to 10 mL in adults, in a dedicated EDTA tube)
(1 to 3mL in a sterile collection tube)
(2 to 5mL in a sterile urine jar)
Collect acute and convalescent (2 to 4 weeks post onset) serology samples. Cross reaction of antibodies to other flaviviruses is possible.
Samples should be sent urgently to the Victorian Infectious Diseases Reference Laboratory (VIDRL) which performs testing for MVE virus and other flaviviruses in Victoria. Request forms should be appropriately labelled and include relevant clinical and epidemiological history including symptom onset, vaccination, travel history and country of birth, to guide laboratory interpretation.
The on-call lab manager at VIDRL should be contacted to provide information on samples being sent. Samples should be transported at 4 degrees Celsius.
Incubation period of Japanese encephalitis virus
The incubation period of JE virus is usually 5 to 15 days.
Public health significance and occurrence of Japanese encephalitis
JE is endemic throughout most of Asia and parts of the Western Pacific region with more than 65,000 cases occurring each year.
JE virus was introduced into the Torres Strait islands in 1995, with two fatal cases of encephalitis, and onto the mainland of Australia (Cape York) in 1998. Seropositive pigs were also detected on the mainland. The most likely source of the outbreak in the Torres Strait islands was Papua New Guinea, where the first human cases were detected in 1997.
In early 2022 JE virus detections in humans, pigs and mosquitoes were reported for the first time in south-eastern Australia (Victoria, New South Wales, southern Queensland and South Australia), much further south than where the virus had previously been detected.
JE virus was detected in Victoria for the first time in February 2022. JE virus was initially detected in pigs, and locally acquired human cases of JE, and virus detections in mosquitoes were subsequently identified. A comprehensive response across human and animal health sectors has been implemented following the first detections of the virus in Victoria and is ongoing.
Reservoir for Japanese encephalitis virus
The JE virus is maintained in enzootic (particular to animals in a geographic area) cycles between birds and pigs; waterbirds (herons and egrets) are the main reservoir for disseminating the virus, while pigs are important amplifier hosts. Pigs do not show signs of infection other than abortion and stillbirth, but have continuing viraemia, allowing transmission to humans via mosquitoes.
Humans and other large vertebrates, such as horses, are not efficient amplifying hosts and are therefore ‘dead-end’ hosts for JE virus.
Mode of transmission of Japanese encephalitis virus
JE virus is transmitted to humans through the bite of an infected mosquito, primarily the Culex species.
People cannot be infected by eating meat. Pork or pork products are safe to consume.
Period of communicability of Japanese encephalitis
There is no evidence of transmission of JE virus from person to person.
Susceptibility and resistance to Japanese encephalitis
Infection with JE virus confers lifelong immunity.
Prevention and control measures for Japanese encephalitis
Treatment of JE is supportive. Suspected cases should be discussed with the local Infectious Disease service.
There are two safe and effective vaccines available to protect against Japanese encephalitis.
A is in place in Victoria to monitor the number and species of mosquitoes, presence of viruses in mosquitoes (including Japanese encephalitis virus) and support local councils to manage the risk of mosquitoes in their local areas.
There is significant global demand for the JE vaccine. Victoria has a limited supply and therefore access is restricted to specific priority groups, targeted to those most at risk. Eligibility criteria will continue to be monitored.
In Victoria, JE vaccine is available free-of-charge for:
High-risk local government areas
People aged 2 months or older who live or routinely work in any of the high-risk local government areas (LGAs) AND:
- regularly spend time engaging in outdoor activities that place them as risk of mosquito bites, OR
- are experiencing homelessness, OR
- are living in conditions with limited mosquito protection (e.g. tents, caravans, dwellings with no insect screens), OR
- are engaging in outdoor flood recovery (clean-up) efforts, including repeated professional or volunteer deployments.*
*Vaccination can be administered before arrival in flood affected areas to those from other regions deployed for recovery efforts by arrangement.
The risk of exposure to mosquitoes is low at an elevation of greater than 500 metres. Therefore, JE vaccination is only recommended for individuals who spend significant time outdoors below this elevation in these local government areas.
- Greater Bendigo
- Greater Shepparton
- Northern Grampians
- Swan Hill
- West Wimmera
No restriction to local government areas
- People who work at, reside at, or have a planned non-deferrable visit to a:
- piggery, including but not limited to farm workers and their families (including children aged 2 months and older) living at the piggery, transport workers, veterinarians and others involved in the care of pigs
- property that has been confirmed to be infected with JE virus
- property suspected to be infected with JE virus
- pork abattoir or pork rendering plant.
- Personnel who work directly with mosquitoes through their surveillance (field or laboratory based) or control and management, and indirectly through management of vertebrate mosquito-borne disease surveillance systems (e.g., sentinel animals) such as:
- environmental health officers and workers (urban and remote)
- All diagnostic and research laboratory workers who may be exposed to the virus, such as persons working with JE virus cultures or mosquitoes with the potential to transmit JE virus, as per the .
Please note, while the vaccine is free-of-charge, some providers may charge an administration or consultation fee. Be sure to check if this applies to you.
Region Contact Barwon South West Gippsland/Latrobe Grampians/Ballarat Goulburn Valley Loddon Mallee Ovens Murray
There are two safe and effective vaccines for JE:
- Imojev®: live attenuated vaccine given by subcutaneous injection. Registered for use in people aged ≥9 months. Primary course is one dose.
- JEspect®: inactivated JE vaccine given by intramuscular injection. Available for use in infants and children aged ≥2 months, immunocompromised people, and pregnant or breastfeeding women. Primary course is two doses.
Imojev® vaccine is prioritised in Victoria’s current public health response.
Most people will develop protection within 14 days of receiving Imojev® vaccine and 28 days following a full course of JEspect® vaccine. It is important that people continue to protect themselves from mosquito-borne disease following vaccination.
Booster doses following previous Imojev® vaccine are not routinely recommended. Eligible persons, who have had a previous course of JEspect® vaccine, should discuss vaccination requirements with their immunisation provider.
JE vaccination is not part of the National Immunisation Program schedule.
Reviewed 12 September 2023