GPs warned to be on alert for Japanese encephalitis

Anastasia Tsirtsakis

10/03/2022 4:18:57 PM

Australia has recorded its second death from the mosquito-borne disease, with cases detected in south-eastern states.

A culex mosquito.
Japanese encephalitis virus is spread from infected culex mosquitoes.

GPs have been urged to be on alert for patients presenting with symptoms of Japanese encephalitis (JE), particularly those practising in rural and remote parts of the country.
The warning comes after NSW authorities confirmed a man in his 70s who passed away on 13 February, died from the mosquito-borne virus. A Victorian man in his 60s also died after contracting the virus last month, bringing the national death toll to two. 
While JE is the most common cause of viral encephalitis in parts of Asia, with occasional incursions in Australia in Cape York, the Torres Strait Islands and the Tiwi Islands, this is the first time the virus has been recorded in southern states.
‘This is very much a surprise and a new development,’ Professor Dominic Dwyer, a medical virologist and director of Public Health Pathology at NSW Health, told newsGP.
‘There’s still a lot we don’t know. But for general practice, particularly those in rural areas or those who may be seeing patients who’ve been in those areas, this is now something to consider.’
The JE virus is transmitted through a bite from culex mosquitoes that have contracted the virus from infected animals, most commonly pigs and certain waterbirds.
To date, the mosquito-borne virus has been confirmed in at least 21 piggeries in NSW, Victoria, Queensland and South Australia.
Once infected, human-to-human transmission is not possible, nor is contracting the virus from touching an infected animal or eating animal products.
Of those who become infected, the majority will be asymptomatic, with less than 1% expected to experience symptoms, which will usually develop 5–15 days after being bitten.
Symptoms include fever and headache, while those who develop a severe illness may experience neck stiffness, disorientation, tremors, coma and seizures.
Children aged under five and older people are at a higher risk of developing severe illness, and though rare, JE has a high case-fatality rate of around 30% among those with symptoms. Of those who survive the acute illness, approximately 50% will have neurological sequelae.
If a patient is suspected to have JE, and to be at risk of severe disease, Professor Dwyer said it is vital that they be transferred to a hospital where diagnostic tests can be run to rule out other causes of encephalitis.
‘Some of the other causes of encephalitis are treatable, for example things like herpes simplex and varicella zoster, which can be confused with bacterial infection,’ he said.
‘So if someone’s got suspected encephalitis you need to get them transferred to a hospital, imaging done, lumbar puncture possible, and the appropriate tests for all the causes of encephalitis to treat the treatable ones or to make the diagnosis.’
If the patient is confirmed to have the JE virus, currently there are no antiviral drugs approved for treatment. Rather, the focus is on prevention, with health authorities urging people to avoid exposure to mosquitoes.
The good news, Professor Dwyer says, is that there is a vaccine available.
‘And it’s a good vaccine,’ he said.  
‘But we’ve got very little of it in the country because it’s really only issued to GPs looking after people going overseas. And there’s no recommendation yet that the community would have this vaccine in Australia.’
Currently, the Australian Immunisation Handbook only recommends routine JE vaccination for laboratory workers who may be exposed to the virus, travellers spending one month or more in endemic areas during transmission season, and people who live or work on the outer islands of Torres Strait.
But Professor Dwyer says the current outbreak situation may signal the need to revisit the vaccination strategies, suggesting people who work in piggeries as a ‘logical place to start’.
Such steps are being taken by the Victoria Government, which has said it is working on making the vaccine more widely available through public health units for people who work with or around pigs.
While culex mosquitoes are very common in Australia, experts say their presence has multiplied as a result of climate change and the La Niña weather pattern, which has seen heavy rainfall and floods.
Professor Dwyer says this has created a perfect storm for the emergence of the JE virus.
‘There’s massive amounts of water in the outback and that has been accompanied by high mosquito numbers,’ he said.
‘So you’ve got the mosquitoes, you’ve got the pigs, which are like an amplifying host of JE, and then you’ve got humans in proximity.’
So is this is expected to be an ongoing issue?
Professor Dwyer says it is still early days, with authorities monitoring the outbreak as it unfolds.
‘When the temperature drops in winter, the mosquitoes go away,’ he said.
‘But we do know that with some of these viruses that the mosquito eggs that might be laid can have the virus in them and they can pop up again next year – we call this “over wintering”.
‘So we don’t know whether JE is going to be a problem next year, or forevermore. But the general message is people need to be aware that this is around; be aware of the disease, be aware of the risk, and know what tests to do if [patients are] worried about it and know that there’s a vaccine.’
Other mosquito-borne diseases
In addition to the JE virus, GPs in south-east Australia are being alerted to other mosquito-borne diseases.
SA Health issued a warning on 27 February after the recent detection of various flaviviruses due to La Niña, including the Kokobera virus in adult mosquitoes in the Riverland and the West Nile virus (Kunjin variant) in horses in NSW in January, urging people to avoid exposure to mosquitoes.
‘In South Australia, there have been seven cases of acute encephalitis identified in the past month, which are currently undergoing investigation for flavivirus infection,’ Deputy Chief Public Health Officer Dr Chris Lease said.
‘All of these people required hospitalisation … and one person having sadly passed away.’
In addition to cases of acute encephalitis, SA Health also noted an increase in the number of Ross River virus cases, with 77 reported in the state, up from 48 at the same time last year.
‘To protect against mosquito-borne diseases, we are encouraging people to “fight the bite” and take precautions such as wearing long, loose-fitting, light coloured clothing and using a repellent which contains DEET or picaridin,’ Dr Lease said.
‘People should also reduce the risk of being bitten by mosquitoes by proofing their homes and by removing any potential breeding sites on their properties.’
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