20 Oct 2017

Rise of rainwaters tanks could attract dengue mosquito back to Brisbane

Could the popularity of rainwater tanks in Brisbane provide the right conditions for the dengue mosquito to return to the city?

The dengue mosquito — Aedes aegypti — has not been detected there for 60 years.

Scientists have used historical data of dengue outbreaks in Brisbane and the mosquito regulations at those times to determine whether there is a link between rainwater tanks and case numbers of dengue fever.

Dr Jonathan Darbro from QIMR Berghofer Medical Research Institute's Mosquito Control Laboratory said the increased use of tanks had added to the risk of reintroducing the dengue mosquito.

"Since the early 2000s more than 300,000 rainwater tanks have been placed in Brisbane backyards," he told ABC Radio Brisbane's Craig Zonca.

"The tanks we have now are different from back in the day, as they were aluminium rust monsters.

"The ones we have now are more well made, and if you install them properly and maintain them there should be no problem.

"Yet the tank needs to be compliant.

"If the outflow pipe is dirty, if the screen or sieve has been taken off or there's a gap, then there's a risk.

"The tanks are then primed to pump out a lot of mosquitoes.

"We need to keep the rainwater tanks maintained."

Dengue once as far south as northern NSW

The scientists' study, titled The Elimination of the Dengue Vector From Brisbane, looked at the role of mosquito surveillance and habitat removal and policy in Brisbane.

It also looked at the link between rainwater tanks and mosquitoes to know why the dengue mosquito was no longer in south-east Queensland.

"Many people don't realise that in the early part of the 20th century the mosquito could be found as far south as New South Wales," Dr Darbro said.

Dengue mosquitoes need warm conditions to survive and they lay their eggs in still water.

"The other thing about the mosquito is that it's a tropical mosquito, so that's why we see it up north," Dr Darbro said.

"The rainwater tank provides a nice volume of water and the water in them doesn't get as cold, even if temperatures outside are cold.

"We think that's the secret to why rainwater tanks could once again help the dengue mosquito live again in Brisbane."

Fix your tanks!!

In the 1910s, mosquito inspectors in Brisbane were appointed to check tanks and ensure mosquitoes were not travelling in and out.

"Nearly 70 per cent weren't compliant in the 1910s and the records showed us that when a number of tanks were fixed then dengue fever began to drop," Dr Darbro said.

"It paints a good picture that the rainwater tanks and extra water source may have played a key role."

The last dengue outbreak in Brisbane was in 1943, and the last time the dengue mosquito was seen in Brisbane was 1957.

Although common in north Queensland, at present the dengue mosquito has only been found as far south as Gin Gin in central Queensland.

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