Mosquito-borne disease risk following flooding and heavy rainfall

The Department of Health is warning people living or traveling to regions impacted by recent flooding and heavy rainfall of the increased risk of mosquito-borne diseases.

Tidal storm surges and flooding associated with heavy rains often produce extensive breeding habitat for mosquitoes. The standing water that remains after tidal and flood waters subside can create an ideal environment for mosquitoes to lay their eggs.

Acting Medical Entomologist at the Department of Health, Dr Jay Nicholson, said that mosquito numbers and notified cases of Ross River virus (RRV) disease were already above average prior to the recent rainfall event.

“We are now expecting mosquito numbers, and the associated risk of mosquito-borne disease transmission, to rise again over the coming weeks,” Dr Nicholson said.

“Whilst RRV is the most common mosquito-borne virus in Western Australia, a small number of Barmah Forest virus (BFV) cases, with similar symptoms to RRV, have also been acquired within the State this year.

“Following recent heavy rainfall across much of northern half of WA, it is also possible that Murray Valley encephalitis and Kunjin viruses may become active in that region.

“Human infection with these mosquito-borne viruses is much rarer than for RRV but the disease they cause can be severe or even fatal.”

Symptoms of RRV disease can last for weeks to months, and include painful or swollen joints, sore muscles, skin rash, fever, fatigue and headaches. The only way to diagnose the disease is by visiting your doctor and having a specific blood test.

There is currently no vaccine or specific treatment for RRV disease, the only way to prevent infection is to avoid being bitten by mosquitoes.

Dr Nicholson said that due to the extensive breeding habitat created by this weather system, it is not realistic to rely on mosquito management alone to control all mosquitoes.

“Individuals residing within the region will need to take their own precautions to avoid mosquito bites.

“Residents of affected areas may be particularly vulnerable to mosquito exposure if insect screening on windows and doors have been damaged. It will be important to ensure all screening is in good working order as soon as practicable in the recovery process, to prevent mosquito exposure in the home.”

Individuals are encouraged to take the following precautions to prevent mosquito bites:
  • avoid outdoor exposure, particularly at dawn and early evening;
  • wear protective (long, loose-fitting, light-coloured) clothing when outdoors;
  • apply an effective personal repellent containing diethyltoluamide (DEET) or picaridin evenly to all areas of exposed skin and always follow the label instructions;
  • ensure infants and children are adequately protected against mosquito bites, preferably with suitable clothing, bed nets or other forms of insect screening;
  • ensure insect screens are in good working order on houses and caravans;
  • use mosquito nets and mosquito-proof tents if sleeping outside;
  • remove water holding containers from around the home and garden to ensure mosquitoes do not breed in your own backyard; and
  • use mosquito coils and mosquito lanterns and apply barrier sprays containing bifenthrin in patio and outdoor areas around houses.
More information about mosquitoes following cyclones and heavy rainfall.

If you think you are too small to make a difference, try sleeping with a mosquito

Dalai Lama