The hidden menace on the rise in Australia's favourite winter holiday destinations

Sydney Morning Herald

a day ago

Of the 13,343 dengue cases reported in Australian between 2012 and 2022, 94 per cent were contracted overseas, mostly from Thailand and Indonesia, a Journal of Travel Medicine study found. One paper estimated six out of every 1000 travellers to high-risk areas catch dengue per month.
Several variants are circulating at once, driving the current outbreaks. Climate change has also expanded mosquito habitats, accelerated breeding cycles and shortened the time the virus needs to replicate within its insect hosts, Dr Gregor Devine at the World Mosquito Program said.
Warmer temperatures may have also weakened a key weapon dispatched against dengue-carrying mosquitoes across Asia and the Pacific, including Australia.
When mosquitoes are infected with a type of bacteria called Wolbachia, their ability to transmit viruses is vastly reduced.
Scientists have bred Wolbachia-infected mosquitoes into local populations around Cairns and Townsville, for example, and almost eradicated local cases of dengue. (A case reported in Cairns in May, however, marked the first locally acquired dengue infection since 2018).
The World Mosquito Program rolled out the technique in two regions of Bali last year and expects it could prevent half a million dengue cases over 15 years. Similar programs are planned or underway in other badly hit countries including Kiribati and Timor-Leste.
The bacteria, however, are sensitive to heat and start to die off within mosquito larva when temperatures surpass 30 degrees, mosquito expert Dr Perran Stott-Ross from the University of Melbourne said.
That could contribute to more dengue cases as hot days and heat waves become more frequent.
'There's a pretty clear link between temperature and Wolbachia loss,' Stott-Ross said. 'We know when Cairns had its hottest day on record several years ago that the Wolbachia took a bit of a hit.'
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There is another proposed dengue-busting proposal on the table, but Stott-Ross is cautious about the idea while the Wolbachia approach remains effective.
UK company Oxitec and the CSIRO have applied to release genetically modified male mosquitoes in Queensland to slash populations of invasive, disease-carrying Aedes aegypti mosquitoes. Oxitec's mosquitos pass on a DNA tweak which kills female larvae.
But Stott-Ross is concerned that could undermine the Wolbachia method if there's a crash in mosquito numbers and then mosquitoes without the bacteria re-populate.
'I think it's a really useful technology. I just don't think there's a need for it in Australia at the moment,' he said.
'We've already got something which seems to be working quite well which is the Wolbachia, and it's already been released pretty much everywhere in Queensland where dengue would be a concern.'
Oxitec said in a statement that having other tools to control mosquitoes 'can only be a good thing for local authorities' given the Wolbachia approach hadn't fully eliminated dengue.
Stott-Ross is researching more heat-tolerant strains of Wolbachia and how mosquitoes could spread under climate change.