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3 November 2011

Ross River virus disease risk spreads in the south-west

The Department of Health is advising people living or holidaying in the south-west of WA to take care to avoid mosquito bites following detection of Ross River virus (RRV) activity at several localities in the region.

Department of Health Acting Medical Entomologist, Dr Peter Neville, said the Department's mosquito and virus surveillance program (undertaken by The University of Western Australia) had detected RRV in mosquito populations at several sites in the Geographe and Leschenault regions, including Busselton, Capel and surrounds.

"Activity of RRV is largely driven by environmental factors including rainfall, temperature and humidity which affect breeding, dispersal and the survival of mosquitoes. Seasons like this with above average late spring rainfall can favour the natural cycle of RRV transmission," Dr Neville said.

The latest activity in mosquitoes follows an initial detection of the virus at one site about three weeks ago and suggests that the range and intensity of activity of the virus in the south-west is expanding.

Symptoms of RRV and Barmah Forest virus (BFV) include painful or swollen joints, sore muscles, skin rashes, fever, fatigue and headaches. Symptoms can last for weeks or months and the only way to properly diagnose the viruses is by a specific blood test. There are no cures or vaccines for these viruses so it is important that people take care to prevent being bitten by mosquitoes.

"Although the current detections of RRV have been in the Geographe and Leschenault regions, people living near tidal saltmarshes and seasonal brackish and freshwater wetlands in other coastal parts of the south-west are also likely to be at risk in coming weeks. The risk may also spread to parts of the Perth metropolitan area if conditions favour continued mosquito breeding," Dr Neville said.

People do not need to alter their plans to visit the south-west as a result of this warning, but it is important to avoid mosquito bites by taking a few simple steps, such as:

  • avoiding areas of high mosquito activity, especially around dawn and dusk
  • wearing protective (long, loose-fitting) clothing when outdoors
  • using a personal repellent containing diethyl toluamide (DEET) or picaridin. The most effective and long-lasting formulations are lotions or gels. Most natural or organic repellents are not as effective as DEET or picaridin or need to be reapplied more frequently
  • ensuring insect screens are installed and completely mosquito-proof: use mosquito nets and mosquito-proof tents
  • ensuring infants and children are adequately protected against mosquito bites, preferably with suitable clothing, bed nets or other forms of insect screening. Only infant-strength repellents should be used on small children

Mosquito management being undertaken by local governments in collaboration with the Department of Health has been underway since early September to reduce mosquito numbers.

"However, it is not realistic to rely on mosquito management programs to keep mosquitoes below nuisance levels, especially when unfavourable environmental conditions reduce the effectiveness of control methods," Dr Neville said.

Some types of mosquito can breed in water-holding containers around houses and the urban environment.

"People can help at home and in the workplace by ensuring that water holding containers are removed or regularly emptied, water tanks are screened at inlet and outlet pipes and ornamental ponds are stocked with fish," Dr Neville said.

Media contact: 9222 4333

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