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What is mosquito-borne Japanese encephalitis?

Japanese encephalitis (JE) is a potentially serious disease caused by the Japanese Encephalitis Virus (JEV).

Recently, human cases of JE have been confirmed in Queensland.

The very first documented case of JE was in Japan in 1871, and prior to February 2022, the last locally acquired human case in Queensland was in 1998.

JEV is transmitted to humans through the bite of a mosquito that has bitten an infectious animal, usually water birds and sometimes pigs.

Fortunately, most human infections of JE cause no symptoms or cause only mild symptoms such as headache or fever.

Rarely, it can cause serious illness and even death.

How it spreads

JEV is a flavivirus, a family that includes yellow fever, dengue, and Zika viruses.

Waterbirds act as a natural reservoir for JEV, and mosquitos infected by biting waterbirds can spread the virus to people, horses, pigs, other birds and animals.

People and horses are considered ‘dead-end hosts,’ as once they are infected, they can’t transmit the virus to anyone else.

This means it can’t be spread between humans.

Pigs and some types of wild birds are called amplifying (or amplifier) hosts, as they allow the virus to multiply quickly to high levels, becoming a source of infection.

JE cannot be caught by eating animal products, including commercially produced pork and pork products.

Increased risks from recent flooding

Recent flooding, and the slow receding of some floodwaters, will likely increase the numbers of mosquitoes in parts of Queensland. This can increase the risk of mosquito bites and transmission of mosquito-borne diseases.

Spread of JE vs COVID-19

COVID-19 spreads between people via aerosolised droplets (tiny droplets that can hang suspended in the air for long periods), like from coughing or sneezing. One person can infect multiple other people.

JEV spreads very differently.

JEV can’t spread without a vector (mosquitos) biting a source of the virus (infected pigs and some water birds) and then biting a person.

An infected person can’t spread JEV to another person because an infected person doesn’t carry enough virus. So even if a person infected with JEV is bitten by a mosquito, and that mosquito bites a second person, the second person won’t get JEV.

Symptoms of Japanese encephalitis

Approximately 99% of JE cases have either no or mild or symptoms, like fever and headache.

A severe infection, although rare, can cause neck stiffness, disorientation, tremors, convulsions, paralysis, coma, and rarely, permanent neurological complications, or death.

Symptoms usually take 5-15 days to develop after the mosquito bite.

Children under 5 and older people are at a higher risk of developing severe illness.

For health advice, call 13 HEALTH (13 43 25 84) or contact your GP.

In an emergency, call Triple Zero (000).


There are no treatments for JE, but you can relieve symptoms by:

  • getting plenty of rest

  • drinking plenty of fluids

  • taking paracetamol for pain or fever.

In more severe cases, hospitalisation for supportive care and close observation may be required.

How to protect yourself against Japanese encephalitis

The best way to protect yourself is to reduce your chance of being bitten by a mosquito and minimise the risk of them breeding in and around your home.

To Reduce Your Chance of being bitten:

  • keep insect screens on doors and windows in good repair, especially in sleeping areas.

  • apply insect repellent containing DEET or picaridin according to the product label directions and precautions.

  • wear long, loose-fitting clothing (light-coloured clothing is best), especially at dusk and in the first few hours after sunset.

  • use plug-in insecticide vaporisers (indoors) and mosquito coils (outdoors).

  • use a mosquito net when camping.

To minimise mosquitos breeding in and around your home:

  • clean up debris, rubbish, and places where water can pool, such as old tires and containers,

  • tip out and wipe plastic containers, bins, boats, bird baths, trailers, tarps, and buckets.

  • store anything that can hold water undercover, in a dry place, or with a lid.

  • reduce the number of bromeliads growing in your garden.

Vaccination against JE

Part of the JEV response will be to support the vaccination of those at highest risk.

There are two vaccines to protect against JE available in Queensland.

The Australian Immunisation Handbook suggests people entering high-risk areas for more than a month, who work with animals, or are travelling to the Torres Strait region or overseas to Asia should consider getting themselves vaccinated.

Currently, the vaccination response is prioritising those at greatest risk for JEV infection, such as workers at piggeries where JEV has been detected.

As the situation evolves, Queensland Health will continue to work with the Australian Government Department of Health as well as the Department of Agriculture and Fisheries to discuss the role and prioritisation of vaccination as part of the national response.

Other mosquito-borne diseases in Queensland

There are several other significant mosquito-borne viruses in Queensland, including dengue, Ross River virus, Barmah Forest virus, as well as a few rarer types.

More information

  • Queensland Government: Japanese encephalitis

  • Australian Government Department of Health: Japanese encephalitis

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