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Disease-Carrying Mosquitoes Figured Out A Way To Survive Winter

The tropical mosquito species that spreads dengue fever is eyeing off your water tank as prime real estate, sparking concerns the disease may have a chance to hit more Australian areas.

The Aedes aegypti mosquito infects hundreds of millions of people across the globe with dengue fever, Zika virus and yellow fever each year.

In Australia, the insect is mostly found in tropical north Queensland, but can also be found living in towns closer to Brisbane.

Previous studies found temperatures in Brisbane were too cold for the insect to survive during the winter months -- but new CSIRO research shows rainwater tanks and even water buckets can provide year-round protection in areas further south.

"If rainwater tanks are not maintained properly, large areas of Southern Australia may see the return of the Aedes aegypti and other exotic disease vectors, bringing with them potentially serious implications for Australian public health," lead researcher Dr Brendan Trewin said.

Dengue fever is similar to a serious case of the flu, and can only be transmitted by mosquitos, not person to person. There is no vaccine or specific medicine to treat it, but most people recover in about a week.

Through a series of experiments, CSIRO found 70 per cent of Aedes aegypti survived to adulthood in water tanks during Brisbane winter conditions, while 50 per cent survived in buckets.

A tank with damage to its top seive. Image: CSIRO

"Rainwater tanks are a buffered environment," Dr Trewin told 10 daily.

"The fluctuations in temperature don't go into the extreme cold, they stay quite warm, so that allows higher survival in the mosquito. This could lead to the return of the mosquito into Brisbane and areas further south."

Out of Australia's major cities, Brisbane has the highest number of rainwater tanks -- with an estimated 40 per cent of properties hosting at least one.

In the early 1900s, up to 90 per cent of the city's population had dengue fever, according to the CSIRO,  but there hasn't been an outbreak in decades.

"The last time Brisbane had significant Aedes aegypti and dengue epidemics, they also had a lot of unsealed rainwater tanks," Dr Trewin said.

"Our research suggests it was the decision to remove these tanks in the 1950s that was one of the keys to driving the disease-carrying mosquito out of the city."

Backyard Biosecurity

The CSIRO isn't suggesting we do away with our water tanks this time, but there is a warning to ensure they are maintained to ensure mosquito and other exotic disease vectors don't make their way further south.

An exposed overflow with no seive to stop insects getting in. Image: CSIRO

"These sort of health threats are a community issue, so we're asking the community to check their tanks," Dr Trewin said.

"Ultimately it's the household's responsibility to make sure they don't have mosquitoes breeding on their property."

It's a matter of biosecurity in your backyard -- the last line of defence should the mosquitoes make their way into different parts of the country from overseas.

Despite efforts by border security officials, Aedes aegypti mosquitos still manage to make their way into Australia via shipping ports in various cities.

Rainwater tank with disconnected outflow. Image: CSIRO

To make sure the insect doesn't get a stronger foothold in Australia, the CSIRO is urging everyone -- though particularly those in Brisbane -- to ensure their water tanks are sealed shut.

How to mosquito-proof your tank:

  • Check there are sieves at the entrance and overflow and there are no gaps
  • Check for cracks in plastic tanks
  • Make sure the sieves aren’t rusting and there are no holes
  • Mosquitos feed on broken down leaves so keep gutters leaf free
  • Check that first flush devices are draining