Authorities this week confirmed the deaths of two men in separate states from Japanese encephalitis, as Australia declared spread of the mosquito-borne virus a communicable disease incident of national significance, with cases detected in several jurisdictions and flooding amplifying the risks of vector-transmitted illness.
NSW Health announced the state’s first-ever death from Japanese Encephalitis virus or JEV in a statement Wednesday evening, a man in his 70s from the Griffith region who died in a Sydney hospital last month and was found on post-mortem to have succumbed to the virus.
It follows a similar statement on Tuesday from Victoria’s Department of Health confirming that autopsy results from a man who died in the state’s north a few weeks ago showed JEV to be the cause of death.
NSW Health said there were now three confirmed JEV cases in NSW residents and another several undergoing testing, while Victoria is reporting seven known cases, Queensland have confirmed a case from the state’s southern region and South Australia is also tracking a fast-growing outbreak.
JEV is a mosquito-borne flavivirus which has its reservoir in waterbirds, horses and pigs, and ongoing flooding across much of Australia’s eastern seaboard mean there is a heightened risk of transmission. 
“We strongly advise people take steps to limit their exposure to mosquitoes and avoid mosquito habitats such as stagnant water,” a Victorian health department spokesperson said. Communities along the Murray River were urged to be especially cautious.
Australia’s acting chief medical officer, Dr Sonya Bennett, declared the emerging JEV situation a communicable disease incident of national significance this week “after determining a national approach is required in relation to coordination of health policy, interventions and public messaging.”
“A national working group of communicable disease, vaccine and arbovirus experts has been established to support the response, including mosquito surveillance and control measures and identification of those at direct risk, and for the rollout of vaccines. Public health communications regarding mosquito protection will target affected communities,” Bennett said.
“The Australian Government’s health and agriculture departments are working very closely with their state government counterparts to ensure a swift and coordinated response.”
Vector-borne climate risks
JEV is spread to humans from horses and pigs via the bite of an infected mosquito. It is not spread between humans and cannot be contracted from consumption of pig products.
While the sequelae from JEV can be serious, even fatal, 90 percent of cases are asymptomatic and less than one percent of people who are infected will go on to become severely unwell with neurological complications such as seizures and coma. Children under five and the elderly are more vulnerable if they contract the virus, and there is no specific treatment available.
Epidemics of JEV persist in Asia despite the availability of an effective vaccine due to flooding and warming, coupled with encroachment on urban areas of pig and other farming. These risks will only be exacerbated by climate change.
This was highlighted in the recent IPCC report, which warned that climate-sensitive food-borne, water-borne, and vector-borne disease risks were projected to increase under all levels of warming, and that these impacts were already being seen. For pathogens transmitted by mosquitoes, shifts in the climate mean a greater range into previously naive populations and niches, and longer seasons for spread.
In an earlier statement on the outbreak, NSW Health noted that JEV was usually confined to far northern Australia and neighbouring countries, and a locally-acquired case had never before been confirmed in animals or humans in NSW.
“NSW Health is cautioning people undertaking outdoor activities such as camping and fishing to carefully consider their plans. This is especially important for people planning activities near waterways or where mosquitoes are present, particularly the Murray River and its branches,” NSW CHO Dr Marianne Gale said.
“People should be particularly vigilant given the recent wet weather conditions, which have led to very high mosquito numbers that may increase further in the coming days and weeks.”
Dr Mark Schipp, Australia’s chief veterinary officer, said JEV had been confirmed at 14 piggeries across NSW, Victoria, South Australia and Queensland. He urged pig farmers to be highly vigilant for unexplained abortions and stillbirths, and said people keeping pigs and horses should practice good biosecurity to control mosquitoes and protect their animals from bites.
Anyone with concerns about a sick animal should contact their local vet or the national emergency animal disease watch hotline, Schipp said.
‘Prevention better than cure’
While a vaccine is available for JEV, it is not routinely offered in Australia nor in abundant supply.
Health Minister Greg Hunt said work was “underway for targeted vaccinations” but “prevention is always better than a cure” and there were simple steps all Australians could take to protect themselves against vector-borne disease.
“We will continue to meet with health authorities in the states and territories to progress the public health response to this disease,” Hunt said.
The most effective strategy is to avoid being bitten, by:
- avoiding outdoor activities at peak mosquito times such as dawn and dusk
- reducing skin exposure by wearing long pants and sleeves outdoors (preferably light-coloured and loose-fitting), and choose permethrin-impregnated garments if spending extended periods outdoors in high-risk locations
- using insect repellents containing DEET, picaridin or oil of lemon eucalyptus on exposed skin and reapplying judiciously
- remove or reduce water containers around the home to limit potential mosquito breeding sites
- use of netting to limit mosquito entry to homes, tents and around sleeping areas
Mosquito expert Cameron Webb said these methods would not only protect against JEV but a host of other mosquito-borne diseases including the related Ross River Virus, which was also subject of an alert from NSW Health on Tuesday after it was detected on Sydney’s outskirts.
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