In Australiaas of April 28, 2022, a total of 37 human cases ofJapanese encephalitis (EJ) (25 laboratory-confirmed cases and 12 probable cases) have been reported in four Australian states, with symptom onset dating back to December 31, 2021. This outbreak represents the first locally-sourced cases detected on the Australian mainland since 1998 Enhanced and targeted surveillance activities are ongoing to better understand the extent of transmission and inform control activities. Further investigation is needed to assess the current risk in Australia.
On 7 March 2022, Australian health authorities notified WHO of three laboratory-confirmed human cases of Japanese encephalitis (JE) (news n°18978 of March 26, 2022). The first human case of Japanese encephalitis was reported on March 3, 2022 in the Queensland. As of 28 April 2022, the Australian Government Department of Health has reported 37 cumulative confirmed and probable human cases of Japanese encephalitis virus (JEV) infection, including three deaths (2 confirmed, 1 probable). Twenty-five confirmed cases have been reported in four states: New South Wales (11 cases, 1 death), Queensland (2 cas), South Australia (3 cases) and Victoria (9 cases and 1 death). In addition, 12 probable cases have been reported in the following states: New South Wales (2 cases), Queensland (2 cases), South Australia (5 cases, 1 death) and Victoria (3 cases).
The number of JE cases and deaths reported in 2022 is unusually high compared to just 15 cases reported in Australia in the ten years preceding this outbreak. Of these 15 cases, only one was acquired in Australia in the Tiwi Islands, in the North territory ; the other 14 cases were acquired overseas. They are also the first known detections of Japanese encephalopathy in humans in these Australian states and the first detections in mainland Australia since a single case was detected in 1998 in Cape York, Queensland.
JEV, which infects both humans and animals, has also been detected in animals in Australia. At the end of February 2022, the presence of JEV was confirmed in commercial pig farms in the states of New South Wales (news n°18854 of February 28, 2022), Queensland and Victoria, then South Australia in early March. The affected barns had experienced unusual levels of reproductive loss and neonatal deaths. As of April 20, JEV has been detected on 73 pig farms across the four states. Prior to February 2022, JEV infection had never been detected in animals further south of mainland Australia than the northern peninsula region of Cape York.
The disease is uncommon in travellers. The prevention of Japanese encephalitis relies on the following strategy.
1. Compliance with individual protective measures against mosquito bites:
- protect yourself against insect bites, in particular by applying repellents, especially on uncovered parts;
- sleep at night under a mosquito net preferably impregnated with insecticide;
- wear light, loose and covering clothing (long sleeves, trousers and closed shoes);
- use clothing impregnated with insecticides for limited periods and in the event of high exposure.
2. Vaccination against Japanese encephalitis:
Its indications were specified in an opinion of the High Council for Public Health of December 20, 2013 and concern:
- travelers required to stay in an endemic area (for whatever duration), with exposure to the outdoors (cycling, camping, hiking, outdoor work), more particularly in rural areas: areas where irrigation by flooding is practiced (rice fields), near pig farms, during an epidemic (or increased circulation of the virus in animals in countries with high vaccination coverage in humans);
- expatriates in a country located in the virus circulation zone;
- any person whose situation is deemed to be at risk by the vaccinating doctor.
The vaccination schedule consists of administering two vaccine doses of 0.5 ml 28 days apart in adults, adolescents and children from the age of 3 years. For children aged 2 months to less than 3 years, two half doses (0.25 ml) are given 28 days apart. It is now possible, in adults aged 18 to 65, to carry out an accelerated regimen in two doses administered 7 days apart. The booster dose(s) administration scheme depends on the persistence of exposure to the risk and the patient’s age.
Sources: World Health Organization (WHO); Australian Government, Department of Health.
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