Course Access
Japanese encephalitis virus (JEV)
JEV is a mosquito-borne flavivirus, it belongs to the same genus as dengue and yellow fever. Japanese encephalitis (JE) is caused by the JEV. The first documented case was in 1871 in Japan (where it gets its name); Australia’s first documented case was in 1995.
In Australia mainland, Japanese encephalitis (JE) remains rare, however is endemic in Asia and Torres Strait region. Australia only had 15 cases notified between 2012 and 2021 – all but one acquired overseas. In 2022 parts of Australia experienced a JE outbreak which was declared by the Australian Government as a Communicable Disease Incident of National Significance. A One Health approach was taken collaborating health, agriculture, water and environment– government state and territory counterparts coordinated responses.
Transmission
JEV is spread through mosquito bites. JE life cycle is commonly between water birds and mosquitoes, however if wild pigs or piggeries are within infected mosquito locations, transmission can also occur to pigs. Horses can also be infected.
Transmission does not occur between humans or between mammals (pigs/horses) and water birds to humans, its also not spread by consuming infected animals. Humans and horses are considered dead end hosts; while pigs and wild birds are deemed amplifying hosts, able to produce sufficient viral blood levels, to infect mosquitoes.
Human Health – Symptoms
Infections are usually asymptomatic, and severe illness and death are rare. Symptoms can include sudden onset of fever and headache. The small proportion of people who experience severe illness (less than 1%) have symptoms of neck stiffness, altered consciousness, focal neurological signs, convulsions, paralysis, and death – indications of encephalitis and meningitis. Symptoms usually present 5-15 days after a person is bitten by an infected mosquito.
JEV Testing
Signs and symptoms can guide testing as well as enquiry into recent travel or visits to areas of JEV exposure. Blood tests and lumbar puncture are used to test for JEV.
Laboratory diagnosis of JE is obtained by testing serum or cerebrospinal fluid (CSF) to detect virus specific IgM antibodies. JE virus IgM antibodies are usually detectable 3 to 8 days after illness onset and persist generally for 30 – 90 days.
Protection Against Jev
Two ways to best protect oneself from JEV: avoid being bitten by infected mosquitoes and vaccination.
Protection from mosquito bites minimises exposure to JEV and other mosquito borne viruses. This includes:
- Using insect repellent approved by the Australian Pesticides and Veterinary Medicines Authority (APVMA) on all exposed skin.
- Wear long loose-fitting, light-coloured clothing when outdoors
- Ensure accommodation (including tents) is properly fitted with mosquito netting and/or screens.
- Cover all doors, windows, vents and openings with insect proof screens
- Remove water holding containers where mosquitoes may breed
- Use insecticide sprays, vapour dispensing units (indoors) and mosquito coils (outdoors) to repeal mosquitos from the area
Vaccination:
High risk groups for the vaccination include:
People who work, reside near or visit piggeries including:
- Farm workers and their families, transport workers, veterinarians and others involved in care of pigs.
- Pork abattoir or rendering plants
People who work directly with mosquito through:
- Surveillance (field or lab based) or control and management
- Indirectly through management of vertebrate mosquito-borne disease surveillance systems (e.g. sentinel animals) such as:
- environmental health officers/workers
- Entomologists.
Diagnostic and research lab workers at risk of exposure and transmission through working with JEV cultures or mosquitoes
Available vaccines:
- Imojev (Sanofi Pasteur) is a single dose, live attenuated virus vaccine (not for pregnant women or those immunocompromised)
- JEspect (Seqirus) is a two dose (inactivated) vaccine which requires a 28-day interval between doses
Resources:
Japanese Encephalitis Virus (JEV) resources
https://www.health.gov.au/resources/collections/japanese-encephalitis-jev-resources
References:
Australian Government Department of Agriculture, Fisheries and Forestry. (2023). Japanese encephalitis virus. Accessed 2024 Mar 13: https://www.agriculture.gov.au/biosecurity-trade/pests-diseases-weeds/animal/japanese-encephalitis
Australian Government Department of Health and Aged Care. (2023). Japanese encephalitis. Accessed 2024 Mar 13: https://www.health.gov.au/diseases/japanese-encephalitis
Centre for Disease control and Prevention. (2023). Japanese Encephalitis Virus. Accessed 2024 Mar 13: https://www.cdc.gov/japaneseencephalitis/index.html
Health Direct. (2023). Japanese encephalitis. Accessed 2024 Mar 13: https://www.healthdirect.gov.au/japanese-encephalitis