Japanese encephalitis (JE) virus is a potentially fatal disease that infects about 100,000 people worldwide every year. Caused by an arbovirus (an arthropod-borne virus), it is transmitted by mosquitoes.
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.
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.
