Dr Chris Rook Adelaide Member TMA
Japanese encephalitis (JE) is a viral disease that can damage the brain and is transmitted by mosquitoes. It is the most common vaccine-preventable cause of epidemic encephalitis world-wide with most cases occurring in Asia. It was first identified in 1935 and it is estimated there are more than 30- 50,000 cases and 10,000 deaths annually. It has recently been reported in Australia Read on for more information
It is a zoonotic disease (can be transmitted from animals) found primarily in Asia, including countries such as China, Japan, and Indonesia, but cases have also been reported in other parts of the world, including the Pacific Islands and more recently within Australia.
In the past, from an Australian perspective, we have viewed Japanese Encephalitis as a disease of travelers and those resident in The Torres Strait. This all changed during the second year of La Nina conditions in 2021/22 when Australia experienced widespread flooding. Usually these conditions would herald outbreaks of Ross River fever and the occasional case of Murray Valley Encephalitis but in the summer of 2021/22 conditions became very favorable for the spread of Japanese encephalitis into certain areas of Queensland, NSW, Victoria and South Australia.
JE is transmitted to humans via bites from infected mosquitoes (Culex species) but is typically maintained in a cycle between mosquitoes and hosts such as pigs and wading birds. Pigs are major amplifiers of the virus, developing high enough viral loads in their blood to infect mosquitoes for around four days.
The disease cannot be transmitted from person to person, but it can be serious, especially in children and the elderly.
Warm areas with large pig populations, such as near intensive piggeries where thousands of animals are crammed into a single shed, are at higher risk of JE (hence the recent issues in NSW).
As mentioned, we now have to contend with JE within Australia. In late February 2022 JEV was confirmed in commercial pig farms in NSW, Queensland, and Victoria. It was also confirmed in SA in March. More than 70 farms were implicated. Prior to this outbreak JE had not been detected south of Cape York.
The total number of confirmed cases in Australia reported on the 5th of Jan 2023 (since 1st Jan 2021):
NSW 14
NT 2
Queensland 2
SA 6
Victoria 3
And another 10 probable cases:
Queensland 3
SA 4
Victoria 3
7 people have sadly died.
What happens if you contract JE?
Currently, there is no cure for Japanese Encephalitis. Treatment is supportive. While the majority of people infected with Japanese Encephalitis will have asymptomatic disease; Symptoms of JE typically appear 5 to 15 days after infection and can range from mild to severe. Mild cases may only cause fever and headache, while more severe cases can lead to inflammation of the brain (encephalitis) and can cause seizures, paralysis, and coma; some will go on to have serious long-term health issues. It is estimated that 1/3 of people who have symptomatic disease will die and 1/3 will be left with neurological impairment. About 1/3 will recover completely.
How can you protect yourself from JE?
There are 2 ways to protect yourself from JEV infection:
- Avoid being bitten by mosquitos
- Receive a vaccination for the virus.
You can protect yourself from being bitten by mosquitos by:
- applying and regularly reapplying an effective insect repellent on exposed skin- the best repellents contain diethyltoluamide (DEET) or picaridin.
- wearing long, loose fitting clothing when outside
- ensuring accommodation, including tents, are properly fitted with mosquito nettings or screens
- using insecticide sprays, vapor dispensing units (indoors) and mosquito coils (outdoors) to clear rooms and repel mosquitoes from an area
- covering all windows, doors, vents and other entrances with insect screens
- removing any water-holding containers where mosquitoes may breed.
Vaccination against JEV is recommended if you are travelling to Asia and the Torres Strait region of Australia and plan to:
- travel in risk rural areas (surrounded by Rice paddies, piggeries, water fowl) and undertake outdoor activities associated with an increased risk of mosquito bites (such as camping and hiking), or will be staying in accommodation without air-conditioning, screens or bed nets
- spend a month or more in a risk region.
There are currently 2 vaccines available for the prevention of Japanese Encephalitis. Both vaccines have been used for many years. Imojev is a live attenuated vaccine and the other is inactivated (Jespect). Both have good protective efficacy and are long lasting. Imojev requires a single dose while Jespect is a 2 dose program separated by 4 weeks. There is an accelerated schedule which can be used. A booster dose is often given for Jespect after 12 months if there is continuing risk. Both vaccines are well tolerated.
Following Covid, most people are now aware that the principal triggers for zoonotic outbreaks are man-made: deforestation, loss of biodiversity, re-zoning of land and the gradual creep of human habitation into wild areas and the climate-induced floods and droughts.
Japanese encephalitis is a serious disease that can have severe consequences, but it can be prevented through vaccination and mosquito bite prevention measures. If you are planning to travel to an area where JE is endemic, it is important to speak with a Travel medicine practitioner about the best ways to protect yourself from the virus.
