Australians tend to think of our 'home-grown' mosquitoes as annoying rather than dangerous. That's a mistake, according to one of Australia's best-known mosquito experts, Dr Cameron Webb, an entomologist based at the University of Sydney. It's true that dengue fever, arguably our best-known mosquito-borne virus, is now well-established in Queensland's tropical Far North. But, dengue owes is higher national profile less to locally transmitted infections and more to the fact that many of the 1238 cases recorded by Aussies this year are holiday mementos, mainly from Indonesia.
However, so-called grey nomads, campers and other domestic travellers – especially those visiting Australia's southern states and regions – often disregard Ross River virus (RRV) and Barmah Forest virus (BFV), two of our country's most significant alphaviruses.
While there's a common misconception that mosquito-borne diseases are only a problem in the northern climates of Queensland and the Northern Territory, some of the biggest outbreaks of Ross River have occurred in NSW, Victoria and southern WA. In 2011, Victoria topped the national list with 1312 cases for the first time in 20 years of record-keeping by the National Notifiable Diseases Surveillance System.
Already this year there's been 3060 cases of Ross River and 3465 of Barmah Forest nationwide and increasingly they are being diagnosed in the south – even in the colder climes of Tasmania.
Domestic travellers should be wary
Wherever they holiday or live in Australia, residents and international visitors can no longer be complacent about mozzie bites. "Australians think of mosquitoes as being a problem only in tropical regions of the world or confined to Australia's north," Dr Webb said.
"The reality is that Ross River and Barmah Forest (viruses) are now commonly reported from southern states. In fact, outbreaks are increasingly occurring on the fringes of cities such as Sydney, Melbourne and Perth."
Perth is expecting a Spring surge of Ross River virus after 31 people contracted the virus in the WA capital and another 8 outside the metro area – double the average – in the month to August 19. The state recorded 1570 cases last year.
Dr Webb predicts that Sydneysiders may also see more mosquitoes this Spring with the Bureau of Meteorology forecasting above average rainfall combined with above average night time temperatures for the next three months. In fact, the bureau suggests that the city will exceed its Spring average of 229.3mm.
Symptoms can be severe – and prolonged
Fortunately, neither Ross River nor Barmah Forest infections are fatal. As with the dengue virus, there's no specific treatment or vaccine, although a vaccine for Ross River is undergoing late-stage human trials.
However, both RRV and BFV can cause very debilitating illness, as 2 recent cases show:
CASE 1 - A Perth woman was bitten by an infected mosquito in the backyard of her Wembley home early this year and experienced fever and aching joints lasting 3 months. Seven months on, Lorraine Featherston is still unable to fully move her fingers, is often tired, and has had to postpone her university studies while she recovers. Read more.
CASE 2 – In January, a Japanese tourist visiting Melbourne was unable to walk after contracting the virus in the city. She was hospitalised and, with treatment, regained her ability to walk, returning home 2 months later to continue therapy. Read more.
Research being undertaken by Dr Webb and UNSW colleagues into Culex molestus, a little-studied mosquito species thought to have been 'imported' into Australia from Japan 50 years ago, could help to determine if it too transmits the Ross River and Barmah Forest viruses. More commonly known as the 'London Underground Mosquito', it is particularly active during the winter months in southern states.
The research has also prompted warnings to local authorities that increasing underground water storage in cities could create new habitats for the species.
How RRV and BFV are spread
- The only way people can become infected is by being bitten by a mosquito that is carrying the virus – not via direct contact with another person or animal. The vector mosquitoes include: Culex annulirostris (common banded mosquito), Aedes vigilax (salt marsh mosquito), Aedes normanensis (floodwater mosquito), Aedes notoscriptus (backyard mosquito).
- The time between being bitten and becoming sick is normally 7-14 days, but can vary from 3 days to 3 weeks.
- Around 1-in-3 people infected with RRV or BFV will develop symptoms, which are remarkably similar and include: painful (sometimes swollen) joints, sore muscles, skin rashes (more common to BFV), fever, tiredness, headaches, and swollen lymph nodes. Wrist, knee, ankle, finger, elbow, shoulder, and jaw are the joints most commonly affected.
- Symptoms eventually subside and leave few if any after-effects.
- If pain occurs, it usually develops rapidly and may be intense. It can be more severe in different joints at different times and when illness is prolonged, symptoms can cause emotional distress - even depression.
- Some adults recover within 2-6 weeks. However, many people will still be unwell after 3 months or, in rare cases, up to a year later.
Avoiding our disease-carrying mozzies
Travellers visiting areas of Australia affected by recent flooding or continuing rain should take measures to prevent mosquito bites – especially at the times of day when the insects are most active.
USE AN EFFECTIVE INSECT REPELLENT – preferably a longer-lasting lotion or gel formula containing an effective ingredient such as DEET, Picaridin, IR3535, or oil of lemon eucalyptus on all exposed skin. Natural or organic repellents are less effective and need to be reapplied more frequently.
COVER-UP WHEN INSECTS ARE ABOUT – Wear long, loose-fitting, light-coloured or protective clothing when outdoors.
PRE-TRAVEL CHECK – Before you leave home, make sure your caravan or tent is in good repair and fitted with snug-fitting flyscreens free of holes or tears.
USE PERMETHRIN – If sleeping under the stars, sleep under a mosquito bed – ideally one that's been soaked in permethrin, an insecticide that repels insects and kills those that come into contact with the treated material. Safe and effective, permethrin can also be used to treat clothing and hats, and continues working even after several washings. Read more.
Guard your home from mozzies, too
Mosquitoes can breed in a variety of places around homes. To breed, they need only a week or so in a small amount of standing water, such as:
- roof gutters
- pot plant drip trays
- garden rubbish
- animal drinking containers, and birdbaths.
It is important to drain or empty these containers once a week.
Septic tanks should be completely sealed to prevent mosquitoes using them to lay eggs and breed. Fit the vent pipe with a mosquito-proof cowl or screen.
Rainwater tanks should be sealed and have insect proof mesh over the inlet, overflow and inspection port.
FOR MORE INFORMATION... Australia's Federal Department of Health and Ageing does not produce public resources on Ross River or Barmah Forest viruses, but does provides links to information provided by State and Territory departments of health.