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Townsville mosquitoes are massing but no health concern for now, authorities say

By Talissa Siganto, Saturday February 9, 2019 - 09:12 EDT

Residents in flood-ravaged north Queensland are being urged to guard against an influx of mosquitoes brought on by several days of torrential rain, but health experts say a sudden spike in dengue fever and Ross River virus is unlikely.

The monsoonal rain event that has over the past fortnight has left behind more than just a muddy mess.

People returning to their homes have been reporting a louder than usual buzz of mosquitoes.

Cameron Webb, a medical entomologist, said it was "no surprise" the region was being invaded by the insect, as it was typical for populations to increase after major flooding events.

"Mosquitoes love to lay their eggs on water or around areas that get flooded with water … without it they can't complete their development so the more water that's about the more mosquitoes are about," he said.

But Dr Webb said the sudden infestation would not cause an immediate outbreak in mosquito-borne disease, because the days directly after a flood were not ideal breeding conditions for the sort that carry the nasty diseases.

"There's lots of water about, it's moving about very quickly and it's actually not very good … what they want is the floodwaters to recede and you start to get these pockets of small shallow stagnant areas of water," he said.

Flooding flushes away disease risks

Steven Donohue, Townsville Public Health Unit director, said there were two broad types of mosquitoes native to the region, each carrying a different health risk.

"The first are mosquitoes that live in and around homes and then there are mosquitoes that live in the bush or swamps," he said.

The mosquitoes that carry dengue fever, Aedes aegypti, are the ones that breed in people's backyards, but Dr Donohue agreed the risk of contracting dengue diminished after an extreme weather event.

"During major flooding events, their breeding sites are washed away and the populations often take weeks to be re-established," he said.

Dr Donohue said the swamp mosquitoes often carried other non-fatal diseases like Ross River virus.

But Dr Webb said the chances of an outbreak of Ross River virus were fairly low, as mosquitoes contracted the disease from infected animals, which often did not survive massive downpours.

"Where there's extensive flooding or there's cyclones hitting a region, sometimes that can be very disruptive for the wildlife as well," he said.

"So the conditions are sort of too intense for both the mosquitoes and the wildlife."

Queensland Health's notifiable conditions report shows there have been 15 cases of Ross River virus within the Townsville Public Health unit since the start of the year, five of which were reported in the last week of January when the severe weather began.

But the report also shows five cases were reported the previous week.

Dr Webb said it was "incredibly difficult" to predict if and when there would be a surge of mosquito-borne disease cases in the region.

"It's often only weeks or maybe months later where you may start to get an increase in mosquito-borne disease risk," he said.

Despite the low risk, experts still urge residents to continue protecting themselves against bites by using a repellent.

It is also recommended that people cleaning up their homes empty any items retaining water to eliminate potential breeding sites.


© ABC 2019

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