Japanese encephalitis virus

Clinical features 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.

Encephalitis cannot be distinguished clinically from other central nervous system infections. Mortality from encephalitis is 20 to 50%. Among survivors, 30 to 50% may have significant sequelae.

Illness usually begins with:

• sudden onset of fever
• headache
• vomiting.

Then over the next few days the following may develop:

• mental status changes
• focal neurological deficits
• generalised weakness
• movement disorders.

Symptoms may also include:

• meningeal signs
• stupor
• disorientation
• coma
• tremors
• generalised paresis
• hypertonia
• loss of coordination.

The following are other recognised presentations:

• A parkinsonian syndrome resulting from extrapyramidal involvement is a very distinctive clinical presentation of JE virus infection.
• Acute flaccid paralysis, with clinical and pathological features similar to poliomyelitis, has also been associated with JE virus infection.
• Seizures are very common, especially among children.

Infectious agent of Japanese encephalitis

Japanese encephalitis virus is a single-stranded RNA virus that belongs to the genus Flavivirus and is closely related to West Nile and St Louis encephalitis viruses.

Diagnosis of Japanese encephalitis

Confirmation of JE virus infection is made by either isolating the virus or by a rising antibody titre, in conjunction with compatible clinical or epidemiological history.

Testing for Japanese encephalitis

Recommended testing for patients with encephalitis, particularly those without another pathogen identified, and with compatible MRI or CT findings, is as follows:

• Blood (serum tube – 2 mL from children, 5-8 mL from adults)
  • Acute and convalescent (3 to 4 weeks post onset) for flavivirus and JEV IgG, IgM and Total Ab
  • Culture/PCR on acute sample
• CSF (at least 1 mL)
  • Flavivirus and JE virus PCR and culture
  • Flavivirus and JE virus IgG, IgM and Total Ab
• Urine (2-5 mL in sterile urine jar)
  • Flavivirus and JE virus PCR and culture

Incubation period of Japanese encephalitis virus infection

The incubation period of JE virus is usually 5 to 15 days.

Notification requirements for Japanese encephalitis virus infection

JE virus infection is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (suspected or confirmed). Pathology services must follow up with written notification within 5 days.

Primary school and children’s services centre exclusion for Japanese encephalitis virus infection
Exclusion from school and childcare is not required for people with JE virus infection.

Primary school and children’s services centre exclusion for Japanese encephalitis virus infection

Exclusion from school and childcare is not required for people with JE virus infection.

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 eastern and southern states of 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

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 virus

JE virus is transmitted to humans through the bite of an infected mosquito. Avoiding mosquito bites is the most important way to prevent JE.

A mosquito surveillance and control program 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 in their local areas.

Vaccination

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 following local government areas of Campaspe, Gannawarra, Greater Shepparton, Indigo, Loddon, Mildura, Moira, Swan Hill, Wodonga, Towong, Benalla, Wangaratta, Strathbogie, Buloke, Greater Bendigo, Hindmarsh, Horsham, Northern Grampians, West Wimmera and Yarriambiack 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.

No restriction to local government areas

• People who work at, reside at, or have a planned non-deferable 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)
  • entomologists.
• 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 Australian Immunisation Handbook.

How to access the vaccine

People listed in the specific priority groups are advised to contact their general practitioner, local public health unit, local council or community pharmacy for more information.

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.

Regional Local Public Health Unit (LPHU)

Metro Local Public Health Unit (LPHU)

Please refer to Local Public Health Units for information on which Local Government Areas fall into LPHU catchment areas.

People living or working in Victoria’s flood-affected areas that do not meet the eligibility for free vaccine can still take steps to keep themselves safe by following preventative measures to protect against mosquito-borne diseases. Visit the Better Health Channel for more information.

Types of vaccines

Imojev® vaccine is prioritised in Victoria’s current public health response.

Imojev®, is available for people aged ≥9 months and requires only a single dose. Imojev® is contraindicated (cannot be given to) in some people because it is a live attenuated viral vaccine (see below). Women should avoid pregnancy for 28 days after vaccination.

JEspect® should only be used for people who meet the vaccination eligibility criteria AND are:

• immunocompromised, OR
• aged 2 months to < 9months, OR
• people requiring their second dose, OR
• pregnant, or breastfeeding OR
• within 6 weeks (preferably 3 months) of receiving immunoglobulins or immunoglobulin containing products.

*For the purposes of JE vaccination, immunocompromise refers to people:

• with immune deficiency (including IFNAR 1 deficiency)
• on immune suppressing therapies, such as chemotherapy, biological or targeted synthetic disease-modifying anti-rheumatic drugs, or on high doses of systemic corticosteroids given for 14 days or more
• with HIV infection with uncontrolled viraemia.

The primary dose of the JEspect® vaccine depends on the age of the person: Refer to the Australian Immunisation Handbook for age related doses and schedule.

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.

Persons who require a booster dose following a previous course of JEspect® vaccine should speak with their immunisation provider. Booster doses following previous Imojev®-vaccine are not routinely recommended.

Please refer to the Australian Immunisation Handbook - Japanese encephalitis for further information regarding JE vaccine to determine eligibility for the vaccine, precautions and contraindications.

Japanese encephalitis vaccination is not part of the National Immunisation Program schedule.

JE eLearning module

Online training has been developed to educate pharmacist immunisers and nurse immunisers about JE immunisation before they can administer the vaccine in Victoria.

Please refer to the Secretary Approvals for pharmacist immunisers and nurse immunisers for information about the scope and requirements of the authorisation.

Access the JE eLearning module.

Resources for health professionals

Japanese encephalitis virus (JEV) – Know the facts about JEV and stay safe fact sheet

Japanese encephalitis eLearning module for professionals

Japanese encephalitis virus: General practice update webinar, 15 March 2022

The Australian Immunisation Handbook - Japanese encephalitis

Japanese encephalitis (JE) vaccination consent form

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Japanese encephalitis vaccine information for immunisation providers

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Japanese encephalitis (JE) vaccine eligibility checklist for the public

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Japanese encephalitis (JE) - Frequently Asked Questions

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