Japanese Encephalitis

Japanese Encephalitis (JEV) is a viral disease transmitted to humans by the bite of an infected mosquito. The mosquito becomes infected after having a blood meal on infected pigs and aquatic birds, which are the virus’ principal hosts. Pigs and aquatic birds are known as 'amplifying hosts', wherein they can have high circulating levels of JE virus without becoming sick and so readily infect a biting mosquito. Other animals (such as horses) can be infected with JE virus but generally are not a 'reservoir' or source of infection to humans.

Japanese encephalitis (JEV) in humans occurs through the bite of an infected mosquito and transmission does not occur from human to humans, nor can it be transmitted through the consumption of pork or pig products. An infected human is not likely to have sufficient viral loads in the blood to infect biting mosquitoes. So humans are known as ’dead-end‘ hosts of the transmission cycle.

Japanese encephalitis is found in many parts of Asia, the Indian subcontinent, Southeast Asia and China. However, it has become more widespread, with cases also occurring in Indonesia, Torres Strait, Papua New Guinea and, in the past, in North QLD.

JEV has now been found in pigs in the eastern and southern states of Australia, and there has been onward spread to humans, resulting in several deaths, via mosquitoes in those areas. These events resulted on March 4, 2022, in the declaration of a Communicable Disease Incident of National Significance by the Federal Department of Health. Read more

You may be advised to have the Japanese encephalitis vaccine if you work, live or plan to travel to a piggery, work in a lab or in the field studying mosquitoes, or a location where the disease is endemic or where an outbreak is occurring.

JE’s cycle of transmission involves the virus’ hosts (wading birds and pigs) and the mosquito that feeds on them (Culex species which feeds at night), becoming infected and transmitting the virus between the hosts and occasionally to humans and horses (both considered dead-end virus hosts, unlike pigs which are known as virus amplifiers).

You cannot catch the virus by eating pig or other animal products.

Potentially JEV-carrying mosquitoes (some Culex spp.) are night-time biters, in particular around dusk and dawn. In temperate endemic areas, humans are more commonly infected in summer and autumn however in tropical areas, JEV circulates more or less continuously between mosquitoes, birds, and pigs.

Transmission occurs in the northern regions of China, Siberia, Korea and Japan in the warmer months of May to October; further south, the peak season is from March to October. In some tropical areas of Southeast Asia and India, transmission depends on the monsoonal rain and bird migration patterns, whereas in areas where there are abundant pigs, rice paddies and birds, transmission can be year-round.

JEV symptoms appear between 5 to 15 days after the bite of an infected mosquito.

About 99 per cent of JEV infections will have no symptoms. Of those people who do get symptoms, most will be mild, cold and flu-like, such as fever, chills, headaches, fatigue, nausea and vomiting.

Symptoms to be aware of are severe headache, neck stiffness, movement difficulties and sensitivity to light and sound, as these may be due to brain inflammation (encephalitis).

In severe cases, the disease can progress to inflammation and swelling of the brain (encephalitis) and often causes seizures that may result in paralysis and coma. The death rate in serious cases is 25-30 per cent, with 30-50 per cent of survivors of a serious infection having ongoing complications. Elderly people, the immuno-compromised and children under five are particularly vulnerable to serious disease.

Diagnosis is based on a combination of clinical signs and symptoms and pathology testing of blood or spinal fluid.

There is no specific treatment for JE. Serious illness is treated with supportive medical therapies and management in hospital.

Mosquito bite prevention is paramount to reducing the risk of infection.

• Use insect repellent containing picaridin, oil of lemon eucalyptus, or DEET on all exposed skin and wear long pants and long sleeves – Read: TRAVELVAX Insect bite prevention measures
• Sleep in air-conditioned or well-screened rooms or tents, or use bed nets impregnated with permethrin
•  Vaccines against JE virus are available. Whether a Japanese encephalitis vaccine is recommended or not should be discussed with a travel health professional – See: TRAVELVAX.

Through the Federal Government, the Communicable Diseases Network Australia (CDNA) has prioritised the groups of people who should be vaccinated against JE using current supplies of vaccine. They include those who work at piggeries/related abattoirs and personnel working directly or indirectly with mosquitoes (surveillance, control etc). Read more. On Aug 4, 2020, NSW Health revised its advice regarding Japanese encephalitis vaccination for nine LGAs in the state’s south to include those ‘aged between 50-65 AND are employed in an occupation that is largely or totally outdoors (defined as spending at least 4 hours per day outdoors).’ Read more. And in Qld, residents of several local government areas were advised that they were considered an at risk group when they participated in  'occupational or recreational outdoor activities undertaken near potentially productive mosquito habitat, such as areas near rivers, ponds and marshes, including flood zones and wherever there are bodies of standing water' and also 'people who live or work in the Torres Strait and/or Northern Peninsula Area of Cape York'. Read more

There are two types of Japanese encephalitis vaccines.

Type: Injectable

• Attenuated live viral vaccine 
• Inactivated virus vaccine  

Contraindications: Should not be administered to individuals who have previously experienced side effects or a serious reaction to this vaccine or who are known to be hypersensitive to any of the vaccine components. The attenuated live viral vaccine should not be administered to anyone who is unable to receive this type of vaccine.

For vaccine details, see the Australian Immunisation Handbook and consult with your GP or Travel Medicine Clinic.

The duration of protection will depend on which vaccine was received in the primary course of vaccination and at what age. Whether boosters are recommended should be discussed with your GP or Travel Medicine Clinic.

The risk to short-term travellers and people who confine their travel to urban centres and use appropriate insect bite prevention measures is very low. Expatriates, travellers living for prolonged periods (over 30 days) in rural, particularly agricultural areas and repeat travellers to locations where JE is endemic or epidemic are at greater risk. Travellers with extensive unprotected outdoor exposure in rural areas, particularly during the evening and at night - especially those engaging in activities such as bicycling, camping or engaging in certain occupational activities in rural areas - may be at high risk, even if their trip is brief.

Travellers are advised to stay in screened or air-conditioned rooms or to use impregnated bed nets when such accommodation is unavailable. Bite avoidance measures such as insecticide, repellents and protective clothing to avoid mosquito bites should be employed.

Through the federal government, the Communicable Diseases Network Australia (CDNA) has prioritised the groups of people who should be vaccinated against JE using current supplies of vaccine. They include those who work at piggeries/related abattoirs and personnel working directly or indirectly with mosquitoes (surveillance, control etc). Read more. On Aug 4, 2020, NSW Health revised its advice regarding Japanese encephalitis vaccination for nine LGAs in the state’s south to include those ‘aged between 50-65 AND are employed in an occupation that is largely or totally outdoors (defined as spending at least 4 hours per day outdoors).’ Read more. And in Qld, residents of several local government areas were advised that they were considered an at risk group when they participated in  'occupational or recreational outdoor activities undertaken near potentially productive mosquito habitat, such as areas near rivers, ponds and marshes, including flood zones and wherever there are bodies of standing water' and also 'people who live or work in the Torres Strait and/or Northern Peninsula Area of Cape York'. Read more

JE vaccine is not routinely recommended for pregnant or breastfeeding women. However, pregnant women at risk of acquiring JE are recommended to receive JEspect as JEV infection contracted during the 1st and 2nd trimesters has been associated with miscarriage. No adverse outcomes of pregnancy have been attributed to vaccination with JEspect. See the: Australian Immunisation Handbook. The live attenuated vaccine is contraindicated in pregnant women (and in the immuno-compromised), and women should avoid pregnancy for 28 days after vaccination with the attenuated virus vaccine.

The CDC states: “Benefits of vaccinating pregnant women usually outweigh potential risks when the likelihood of disease exposure is high, when infection would pose a risk to the mother or fetus, and when the vaccine is unlikely to cause harm.”

Breastfeeding women who are at increased risk of acquiring JE are recommended to receive JEspect. Australian government and other health professional organisations state that, in general, inactivated vaccines given to nursing mothers are safe for both the mother and child. For details, READ: Vaccination Safety for Breastfeeding Mothers

The Japanese encephalitis virus (JEV) has been detected in more than 70 piggeries across Victoria, New South Wales, Queensland and South Australia, and human cases (and deaths) have been reported.

The occurrence of Japanese encephalitis (JE) virus infections in pigs and people in mainland Australia has been of significant concern at the national level, leading to the Australian Acting Chief Medical Officer's declaration of a Communicable Disease Incident of National Significance in consultation with the Australian Health Protection Principal Committee. The formation of an interdisciplinary working group and collaboration with the state and territory officials is a timely response.  Read more

Pig farmers and people who work around piggeries or partake in occupational or recreational outdoor activities near mosquito habitat in affected regions are at the highest risk of infection, particularly if no mosquito bite avoidance measures are taken.

The effective and widely-used Japanese encephalitis vaccines used in Australia (dependent on supplies) have costs ranging up to $300 for travellers. 

However, as of September 14, 2022, and after the recent outbreaks, NSW has expanded free access for Japanese encephalitis vaccine to people considered at risk and living in affected regional areas. NSW Health conducted a survey in several of the towns, and of those residents who took part, one in 11 showed evidence of past infection.

The duration of the Japanese encephalitis vaccination is not known.