It might be the end of summer, but mozzies are still an issue. Ross River Virus disease can be very unpleasant!

There has been a large increase in Ross River Virus cases in Queensland during February/ March. It is much greater than for the same period last year. There are concerns that numbers may surge due to increased exposure of holiday makers over the Easter break. It may be the start of a larger outbreak.

Approximately 4000 cases are reported in Australia each year. The numbers over the past 12 months have been lower than expected.

What is Ross River Virus (RRV) disease?

Ross River Virus is a viral disease which is transmitted to people by a mosquito bite. It is not spread from person to person. It is the most common mosquito-borne disease in Australia. It is also found in Papua New Guinea and the Solomon Islands. Outbreaks have also been reported in Fiji, New Caledonia, Samoa, and the Cook Islands.

The disease is also known as Ross River Fever and is characterised by several signs and symptoms. These include fever, rash, severe lethargy, and joint symptoms. The joint component can be very debilitating, and the lethargy long lasting.

It is possible to have RRV disease and not have fever or joint issues. Severe lethargy might be the only symptom of recent RRV disease. This is why the term RRV Disease rather than Ross River Fever is now being used.

Many infected people have no symptoms.

No deaths have been attributed to the disease, but long-term symptoms are common. A second bout of RRV disease would be unusual.

Infection rates relate to mosquito numbers. This is dependent on environmental factors. It is much more predictable in tropical environments than in temperate areas. Rainfall is the most important risk factor with many more cases reported during the summer months (wet season), and autumn.

RRV disease is reported in all states of Australia. Almost 50% come from QLD, followed by WA and NSW.

What is the source of the virus?

Macropods (wallabies, kangaroos) are the main reservoir of the disease. Possums are a likely source in urban areas. Horses may also be an amplifying host like macropods.

Who is at risk of RRV disease?

Individuals who are living, travelling, or working in areas with bodies of water and mosquitoes are most at risk of the disease. Warnings must be heeded if an outbreak is reported. The more bites the greater risk of the disease. It should also be recognized that some individuals are more attractive to mosquitoes than others. While there is much debate on why this is the case, it should be accepted that some individuals need to show much greater attention to mosquito-avoidance measures.

How is RRV disease prevented?

There is currently no vaccine for RRV. The disease is avoided by reducing your risk of mosquito bites.

Mosquito-borne diseases are best avoided via methods of bite-prevention.

• Reduce exposure time by modifying activities during peak biting times. Highest risk times are around dusk and dawn.
• Wear light-coloured clothing, and cover arms and legs as much as possible.
• Avoid highly scented perfumes, deodorants, or toiletries.
• Manage possible breeding sites if a long-term resident in a high-risk location.
• Use mosquito repellents on exposed skin (see below).
• Use insecticide aerosols, mosquito coils or other agents in the immediate environment.

Repellents

The repellent of choice should contain DEET (N, N-diethyl-meta-toluamide). The higher the concentration of DEET, the longer the duration of protection. However, there is no added benefit beyond 50% DEET concentration. DEET is toxic when ingested and may cause skin irritation in some people. If you have not used a DEET product before, or you have sensitive skin, it is advisable to test on a small area of skin before applying to larger areas of the body.

DEET has been used over a long period of time, and by many millions of people with few reported serious side effects. Despite this, a few precautions should be undertaken:

• Apply DEET lightly to exposed areas only. Consider potential run off with sweating and reapply if mosquitos begin to land.
• Where possible, wash off on returning indoors.
• Do not apply to open cuts or sores.
• Do not use aerosol applications to the face directly.  Apply to the hands and then rub on the face avoiding the eyes and mouth.
• Do not allow children <10 years to apply themselves.  Weaker DEET formulations (10% DEET concentration) are available for children.
• If sunscreens are to be used with repellents, then the sunscreen should be applied first.  Wait 20 minutes before applying repellent.
• Be aware that people tend to underuse repellents.
• There are alternatives to DEET repellents. Picaridin 19% can provide an equivalent level of protection.

RRV is a notifiable disease in Australia.