Perfect storm for high disease risk

HEALTH authorities are bracing for the largest outbreak of mosquito-borne diseases for many years on the back of a bumper mosquito breeding season.

Coastal mosquito populations are due to explode next month due to a combination of warm weather, rainfall and high tides.

There were five confirmed cases of Ross River fever and the same number of confirmed Barmah 

Forest infections in the Hunter New England Health area in the past month.

Saltmarsh mosquitoes in coastal areas can be carriers of Barmah Forest infection, while freshwater breeding mosquitoes inland can transmit the Ross River virus.

Mosquito researcher Cameron Webb described the present conditions as a “perfect storm”.

“When you get rain and tides combined you get a double whammy because you have groups of mosquitoes coming out of two different habitats – all at the same time,” he said.

“The really hot weather we are getting is starting to dry out some of those habitats. We are also expecting some really big tides in the first week of January.”

About 10 days after that we will start to see a big boost in mosquitoes.”

Large numbers of mosquitoes are also breeding in backyard ponds and guttering, Dr Webb said.

He warned there was a high risk of an increase in Ross River fever cases in the second half of summer.

“I think one of the things to be mindful of is that we haven’t seen a lot of activity of Ross River virus along the coast in recent years, so we are all mindful of the potential that we are going to see more 

activity this year,” he said.

“[The] activity of Ross River virus doesn’t stay low for many years in succession.

“For every year we get a period of low activity, a more serious year is not far away.”

Dr Webb, a clinical lecturer in medical entomology at Westmead Hospital and Sydney University, has been studying mosquito populations in Hexham Swamp as part of a Hunter-Central Rivers Catchment Authority project to monitor the impact of the reopening of the Ironbark Creek floodgates.

The study found there was a steady increase in mosquito predators such as birds and fish since the staged opening of the gates in 2008. 

As a result, the swamp’s mosquito population has started to decline.

Hunter New England Health public health physician David 

Durrheim said people should take steps to avoid being bitten by mosquitoes.

“These viruses are spread by mosquitoes that feed on animals that have the infection,” he said.

Symptoms of Barmah Forest or a Ross River virus infection include fever, skin rash, painful joints and tiredness.

Dr Durrheim said as there was no specific treatment available for these mosquito-borne viruses, prevention depended on avoiding mosquito bites and and minimising potential mosquito breeding sites.

That was especially important in the summer and autumn months when infections peaked.

HOW TO AVOID BEING BITTEN

* The danger times of the day are before dawn and after dusk. 

* When outside, wear loose fitting, light-coloured clothing that covers your arms and legs.

* Use an insect repellent that contains the chemical DEET or picaridin on exposed skin.

* Fit flyscreens to all windows and doors.

* If mosquitoes are inside the house, use a knockdown insecticide in bedrooms half an hour before going to bed, according to instructions.

Source: Hunter New England Health

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