Japanese encephalitis

Encephalitis is inflammation of the brain tissue and is usually caused by an infection. Japanese encephalitis (JE) is a potentially fatal disease caused by the Japanese encephalitis virus.

How it is spread

The virus is spread by the bite of an infected mosquito. It cannot be spread from person to person.

Pigs and wild water birds play an important role in the spread of the virus. It multiplies in infected pigs, leading to very high levels in their blood.  Mosquitoes feeding on infected pigs are highly likely to pick up the virus and may then spread it to humans.

Where and when the virus is found

The virus has been found throughout Asia and in the Torres Strait region of Australia. To date only one case has been acquired in the Northern Territory (NT).

In 1995 the first case in Australia was reported from Badu Island in the Torres Strait. The virus is thought to have spread south from Papua New Guinea.  Since 1995 there have been 6 cases (including 3 deaths) in Australia. Four of the cases have been acquired in the Torres Strait, one from the mainland on Cape York Peninsular and one on the Tiwi Islands in 2021.

The risk to humans is higher during or just after the wet season. This is when large numbers of the common banded mosquito are present.

Humid conditions allow mosquitoes to live longer. It provides more chances for a mosquito to pick up the virus from an animal and live long enough to pass it on to humans.

One case of the virus was transmitted in the NT but the virus has not yet been found in host animals or mosquitoes in the NT.

The mosquitoes capable of spreading the virus are found in the NT.


It usually takes 5 to 15 days between getting bitten and becoming unwell.

Symptoms include:

  • headaches
  • fever
  • seizures or fits (especially in young children)
  • neck stiffness
  • drowsiness
  • confusion and progression to delirium and
  • coma in severe cases.


There is no specific treatment for JE disease.


A vaccine is available and is recommended for:

  • travellers spending a year or more in Asia (except Singapore), even if most of the stay is in urban areas.
  • all residents (over 1 year of age) of the outer islands in the Torres Strait.
  • anyone who will be living or working on the outer islands of the Torres Strait for a cumulative total of 30 days or more during the wet season (December to May).
  • travellers spending 1 month or more in rural areas of:
    • Papua New Guinea
    • East Timor or
    • Asia.

A vaccine should also be considered if :

  • travel is during the wet season
  • there is a lot of outdoor activity or
  • the accommodation is a low standard.

Personal protective measures

You can protect yourself against the virus by doing the following:

  • avoid areas with numerous mosquitoes in close proximity to wet lands where birds and feral pigs might be present
  • wear protective clothing outdoors and cover feet, legs, and arms. Loose, light-coloured clothing is best
  • avoid being outside when vector mosquitoes are most active. Just before sunset, during the night and early in the morning
  • use personal repellents containing diethyl toluaminde (DEET), picaridin or PMD (extract of lemon eucalypt) on areas of exposed skin
  • use mosquito coils, candle heated or gas operated devices with insecticide treated pads in sheltered or low wind outdoor areas.
  • make sure fly-screens in houses or caravans are in good condition
  • If camping, sleep in a mosquito-proof tent or under a mosquito net

Repellents only protect against mosquito bites for up to 4 hours, not all night.

Read more about protecting yourself from mosquitoes to prevent mosquito borne disease.


JE is a potentially fatal disease, however only 1 in 30-300 people bitten by an infected mosquito will become ill.

10 to 30% of people who develop the disease will die. 50% will recover but have permanent disability and 25% will recover completely.

Children under 15 years of age are at greatest risk of developing a severe disease.


For more information about mosquitoes and virus ecology contact your nearest Centre for Disease Control or go to the Department of Health website.

Last updated: 05 October 2021

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