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20 March 2012

Mosquito-borne disease threat continues across WA

The Department of Health is reminding residents and travellers throughout Western Australia to take precautions to avoid mosquito bites. The warning follows continued activity of mosquito-borne diseases across WA.

Ross River virus (RRV) and Barmah Forest virus (BFV) are active in parts of Perth and the South West, while RRV and Murray Valley encephalitis (MVE) virus are active in the north of the state.

The above-average activity of RRV in the South West and Perth was predicted in October 2011 and has continued throughout Summer and early Autumn. Above average rainfall, higher than usual minimum temperatures and recurrent high tides have enabled extensive breeding of mosquitoes and ongoing transmission of RRV.

Department of Health Acting Medical Entomologist Dr Peter Neville said Ross River virus continued to be active throughout most parts of WA, with 1153 cases reported to the Department of Health since July 2011. This includes more than 500 people who are likely to have been infected in Perth - a record number for a single RRV season.

"Areas of greatest concern include Perth (particularly suburbs with substantial natural wetlands and bushland), the South West, Great Southern and Wheatbelt," Dr Neville said.

"We are also starting to see an increase in the number of cases of RRV from the north of WA, associated with wet season rainfall," he said.

"Local Governments and the Department of Health have had collaborative mosquito management programs in place since the elevated risk of mosquito-borne diseases was first identified.  However, the sheer size and inaccessibility of natural mosquito breeding habitat in many areas of WA, including some parts of Perth, means that it is often not possible to reduce mosquito populations to levels that don't pose some risk to public health."

Symptoms of RRV and 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 confirm infection is through specific blood tests organised by a doctor. There are no cures or registered vaccines for these viruses so it is important that people take care to prevent being bitten by mosquitoes.

The Department of Health's sentinel chicken surveillance program (undertaken by The University of Western Australia) has continued to detect activity of MVE virus in the Kimberley and Pilbara, and of the closely related Kunjin (KUN) virus in the Gascoyne, Midwest and Wheatbelt. The Department is concerned that a recent increase in wet season rainfall in the north-west may further increase the potential for transmission of these viruses.

"Murray Valley encephalitis is a rare but potentially serious disease with initial symptoms including fever, drowsiness, headache, stiff neck, nausea and dizziness."

"People experiencing these symptoms should seek medical advice quickly. In severe cases, people may experience fits, lapse into a coma, and may be left with permanent brain damage or die.

"In young children, fever might be the only early sign, so parents should see their doctor if concerned, particularly if their child experiences drowsiness, floppiness, irritability, poor feeding, or general distress.

"Kunjin virus usually causes a milder illness than MVE virus, but in rare cases also causes severe symptoms, including headache, neck stiffness, fever, delirium and coma," Dr Neville said.

People living or travelling in WA do not need to change their travel plans but should take extra precautions to avoid mosquito bites, such as:

  • avoiding outdoor exposure particularly around dawn and dusk (however some species of mosquitoes may be active throughout the day and night);
  • wearing protective (long, loose-fitting) clothing when outdoors;
  • applying a personal repellent containing diethyl toluamide (DEET) or picaridin to exposed skin or clothing. The most effective and long-lasting formulations are lotions or gels.  Natural or organic repellents may not be as effective as DEET or picaridin, or may need to be reapplied more frequently;
  • ensuring insect screens are installed and in good condition. The use of bed nets will offer further protection;
  • using mosquito nets or mosquito-proof tents when camping or sleeping outdoors; and
  • ensuring infants and children are adequately protected against mosquito bites, preferably with suitable clothing, bed nets or other forms of insect screening.

Media contact: (08) 9222 4333

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