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Most JE virus infections in people cause no symptoms, but in rare cases it can develop into a serious infection of the brain called encephalitis.

Japanese encephalitis is an arbovirus (an arthropod-borne virus), transmitted by mosquitoes.

JE occurs throughout most of Asia and parts of the western Pacific, including neighbouring Papua New Guinea, and is the most common cause of human viral encephalitis in Southeast Asia.

Even though an effective vaccine is available, JE still poses a threat to our region, including Australia. So we're working on ways to prevent it from spreading further on our shores.

Transmission of the virus

The JE virus is maintained in the environment in a transmission cycle between mosquitoes and animal hosts.

Research has shown that some animals develop more virus than others. These animals are called 'reservoir hosts' because the virus circulates in their system for longer and at higher concentrations, providing more opportunities for blood feeding mosquitoes to pick up and transmit the virus.

The 'reservoir hosts' for JE are primarily pigs and waterbirds. Occasionally an infected mosquito will transmit the virus to a human. Humans don't contribute to the environmental transmission cycle as we do not create high concentrations of virus in our blood.

Japanese encephalitis in Australia

In 1995, there was an outbreak on the islands of the Torres Strait. The outbreak was unprecedented because it had never before been detected this far southeast.

Isolated cases also occurred in the Torres Strait islands and Cape York Peninsula in 1998.

More recently, JE has also been found in the northern parts of Cape York Peninsula of Queensland and in early 2021, the first case of JE was reported in the Tiwi Islands of the Northern Territory. This was the first locally acquired human case in Australia since 1998.

The 2021 case was found to be caused by a particular type of the JE virus (genotype 4) that had previously only rarely been found, and mainly in Indonesia, but we also now know that it exists in Papua New Guinea.

In late February and early March 2022, a widespread outbreak of JE occurred in piggeries in southern Queensland, New South Wales, Victoria and South Australia.

Our scientists at ACDP are assisting with the outbreak response. They are heavily involved in diagnostic testing for affected states, particularly for piggeries suspected of being infected.

As part of this ongoing diagnostic support, ACDP scientists have provided information and advice to animal and public health laboratories on laboratory diagnostics. This has included testing guidelines and information, including the first genome sequence of the outbreak strain, to assist accurate diagnostic testing.

Our scientists have also been providing expert advice to various government and animal health working groups involved in outbreak response. These groups are working closely with public health counterparts in a One Health approach to coordinate and manage the outbreak in Australia.

The importance of monitoring and surveillance

The Australian Government and some states and territories have established mosquito surveillance programs. These monitor relative abundances of a range of mosquito species at various sampling sites.

In addition, the Department of Agriculture, Water and the Environment (DAWE) oversees the Northern Australia Quarantine Strategy (NAQS) which is responsible for identifying and evaluating risks of pest incursions. NAQS provides early warning of quarantine pests through a program of monitoring, surveillance and public awareness across northern Australia and in neighbouring Indonesia, East Timor and Papua New Guinea.

Scientists at our Australian Centre for Disease Preparedness (ACDP) provide diagnostic testing services for this surveillance program and others, including the National Arbovirus Monitoring Program and the National Transmissible Spongiform Encephalopathies (TSE) Surveillance Program.

Establishing surveillance systems in PNG

ACDP scientists are leading a project working with local organisations in Papua New Guinea to develop pilot surveillance activities for mosquito-borne diseases.

Pigs are critically important to the livelihoods of rural farming communities in PNG and are kept in close proximity to people, increasing the chances of JE transmitting to humans.

The project team adopted a One Health approach that recognises the health of people, animals and the environment are interconnected.

Our scientists and those from partner organisations worked with human and animal health organisations in PNG to establish both mosquito and sentinel animal surveillance.

In this case, the sentinel animals used were pigs, because the JE virus cycles between mosquitoes and pigs. Pigs are critically important to the livelihoods of rural farming communities in PNG and are kept in close proximity to people, increasing the chances of the virus transmitting to humans.

In mid-2020, after the detection of African swine fever (ASF) in PNG, the scope of this project was expanded to incorporate surveillance and testing for ASF.

The project is now complete, having delivered training and development activities for the establishment of field-based surveillance and for laboratory diagnostic methods, including tests for mosquito-borne viruses and more accurate tests for the detection of ASF.

Working with our close neighbours provides important information around the ongoing risks of these viruses and other animal diseases arriving on the Australian mainland.

Our ongoing role

Our research is helping Australia and the region respond to potential exotic disease incursions.

As a nationally recognised reference laboratory for arboviruses, ACDP and our scientists maintain the capability to diagnose and characterise diseases, and work to develop new and more accurate testing methods.

Our researchers also provide important technical advice as members of national and international advisory committees. For example, as members of the National Arbovirus and Malaria Advisory Committee (NAMAC), ACDP scientists provide expert advice on arbovirus and malaria surveillance, disease management and vector control.

Read more about our work in PNG: Zapping away mosquito-borne diseases in Papua New Guinea.

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