Ross River Virus

Ross River Virus Fact SheetNovember 2002

Ross River Virus is an illness caused by infection with the "Ross River" virus. Many people infected with Ross River Virus (RRV) (particularly children) have no symptoms.

What symptoms can Ross River Virus cause

Symptoms when present include fever, headache, aches and pains in the muscles and joints and in about 50% of people a rash . In the majority of cases, symptoms disappear within 6 weeks. Ten percent of people can feel depressed and have fatigue affecting their activities of daily living for up to 6 months.

(a)It is important to note that 100% of affected people recover completely in due course with no residual effects.

(b)Those affected by the infection gain life-long immunity against future infection.

(c)Many people infected with the virus, particularly children, have no symptoms but go on to achieve life-long immunity. Most of the cases notified in Tasmania have been in people aged over 40

How it is Spread?

The infection is spread by infected mosquitoes. In large outbreaks, mosquitoes may also spread the virus from infected people to other people. However, large outbreaks usually involve hundreds of cases occurring in a short period of time. This situation has not arisen in Tasmania.

Only a few species of mosquitoes are capable of transmitting RRV in Tasmania. The risk of contracting RRV depends on various factors such as,

• mosquito activity, which in turn is related to heavy rain and high tides that provide habitat areas for mosquito breeding. Other climatic factors including temperature, humidity and wind strength and/or direction are also important factors, and
• proximity to mosquito species that can transmit RRV and wildlife that carry RRV.

Trapping adult mosquitoes (and testing to see if they are carrying the RRV) and identification of mosquito larvae in habitat areas has determined that mosquitoes primarily responsible for transmitting RRV in the Sorell Municipal Area breed in salt marshes and estuaries, not saltwater rock pools, fresh water lakes or wetlands, water tanks or drains.

Mosquitoes that transmit RRV can fly or be wind blown many kilometres from breeding sites. Adult mosquitoes rest in vegetation after feeding but do not breed in these areas. People living close to salt marsh habitats should pay particular attention to how RRV can be prevented.

How long does it take for Ross River Virus to appear?

The incubation period ranges from 3-11 days (often 7 - 9 days).

Can an affected person infect others?

Direct person-to-person spread very rarely occurs as explained above.

How would I know if I have Ross River Virus?

A variety of blood tests are used to demonstrate the presence of specific antibodies to Ross River Virus. It takes a couple of weeks before these antibodies appear in the blood. If symptoms are persisting longer than 6 months it is very important to see your doctor as some other medical conditions can be very similar to RRV.

What treatment is available?

There is no specific treatment for the virus however pain and fever symptoms can be alleviated by the use of analgesics such as Paracetamol. Anti inflammatory medications may be used for treating arthritics symptoms and people should seek medical advice.

How can I prevent Ross River Virus?

The mosquito that is known to carry RRV is most likely to bite humans at dawn and around dusk. Self-protection is the most effective way of preventing infection. The following measures are effective methods of personal protection:

• Wear loose fitting, light coloured clothing covering up as much of the body as possible. Mosquitoes can bite through tight fitting clothing (eg, jeans).
• Use effective insect repellents (suc as those containing DEET - Diethyl toluamide) to cover areas of exposed skin. Always read the manufacturer's instructions prior to application.
• Wash DEET off before going to bed in the evening. Do not use on infants if the DEET concentration exceeds 20%.
• Use 1mm insect screens on your house, caravan or tent. If this is not possible, use a mosquito net.
• Remember that adults are more at risk of this infection than children.

Where are Ross River Virus-carrying mosquitoes found?

In Tasmania the coastal regions extending from the North (including the islands of eastern Bass Strait), down the East and South Eastern corner have all shown to be ideal for the transmission of RRV. The most common sites within these coastal districts are salt marshes (which are adjacent to the coast), which provide ideal mosquito breeding sites.

Tasmania is home to about 30 species of mosquitoes that breed in still water in fresh and salt water environments. Only two of these are important in RRV transmission. However, if mosquitoes are a nuisance around your house, this problem can be reduced by removing any containers that collect water. Also, it is recommended for households on tank water that tank intakes and overflows are sealed with 1 mm insect screen and that tanks and roof gutters are cleaned periodically.

Ross River virus infection is a Notifiable Disease.

Adapted from "You've got What?" with the permission of the Department of Human Services, South Australia.
Chin, James MD, MPH Editor, Control of Communicable Disease Manual 2000
Acknowledgement
Dr Owen Seeman, DPIWE 2002