A modeling study suggests the possibility of a Japanese encephalitis virus outbreak in Australia

A modeling study suggests the possibility of a Japanese encephalitis virus outbreak in Australia

Paper from a research team incorporating mathematical modeling expertise from LSHTM and led by the QIMR Berghofer Medical Research Institute in Brisbane has suggested up to 750,000 people across Australia could be at risk of exposure to Japanese encephalitis (JEV).

The modeling study, published in Clinical Infectious Diseases, suggests the possibility of a major outbreak of the virus in Australia's summer months (December to February), which could be driven in part by a third La Niña in as many years.

There have been 31 confirmed human cases and six deaths so far in 2022. JEV is found in wild birds and is spread by mosquitoes between these hosts and other animals, including pigs, humans and horses. The virus has spread across Australia this year and there have been confirmed cases in dozens of pig farms across the south of the country. There have also been confirmed cases of JEV in wild boar in the Northern Territory and Queensland. Until last year, YEV was limited to Asia and the far north of Australia.

The widespread La Niña weather event is believed to be responsible for the virus spread, as increased rainfall and flooding created new wetlands that attract infected waterfowl and provide breeding grounds for the common vector mosquito Culex annulirostris.

The paper points out that if pigsties become a source of infection, anyone living within four kilometers of an infected pigsty is potentially at risk. This is because the mosquito responsible for spreading JEV is a strong flyer.

Most Australians have never been exposed to the virus and therefore have no immunity. We urge people to take precautions. The best protection is a vaccination, but this is not currently available to everyone. The next best protective measure is to avoid being bitten by a mosquito.”

Greg Devine, associate professor, head of the QIMR Berghofer Mosquito Control Laboratory and senior author of the paper

Associate Professor Laith Yakob, an infectious disease epidemiologist at LSHTM who collaborated on the research and provided modeling expertise, said: “The modeling and mapping we carried out allowed us to estimate the population potentially at risk and therefore the potential number of vaccine doses required.” We also learn where these vaccines could be used. The models will also help us identify locations for increased surveillance efforts to better protect Australian residents in future mosquito seasons.”

The modeling complements blood tests conducted in New South Wales which found almost 9% of participants were infected with JEV, suggesting the virus is common in these areas. However, it is difficult to accurately measure the spread of JEV because only 1% of those infected show symptoms ranging from fever to severe encephalitis. For those who develop symptoms, the mortality rate is about 30%.

In addition to the limited number of human vaccines, there are currently no approved vaccines for pigs or horses in Australia. If JEV continues to spread, the impact could be economically devastating for pig farms and the horse industry.

Associate Professor Ricardo Soares Magalhães from the University of Queensland (UQ) School of Veterinary Science, director of the Queensland Alliance for One Health Services and co-author of the study, said: "The virus is spreading rapidly through the ..." [pig] herd, leading to abortions and stillbirths. In horses, JEV is largely asymptomatic, but when symptoms do occur the mortality rate is very high, particularly in foals, with approximately half of all symptomatic cases dying. UQ, in collaboration with other institutions, is accelerating the development of a vaccine for horses.”

Source:

London School of Hygiene & Tropical Medicine (LSHTM)

Reference:

Yakob, L., et al. (2022) Occurrence of Japanese encephalitis in Australia: the potentially vulnerable population. Clinical infectious diseases. doi.org/10.1093/cid/ciac794.

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