Murray Valley encephalitis (MVEV) is the most serious of the endemic arboviruses in Australia with a 15-30% fatality rate. This is similar to the recently introduced Japanese encephalitis virus.
Large outbreaks of MVEV are uncommon (58 cases in 1974, 17 cases in 2011, 26 cases in 2023) but individual cases occur sporadically across high risk regions.
The transmission cycle is maintained via viraemic water birds and the freshwater mosquito Culex annulirostris. Culex annulirostris mosquitoes are found throughout Australia and are usually active from mid-spring to late autumn in south-eastern Australia and all year in northern parts of the country. Mosquito activity is more likely after heavy rainfall and flooding, or around wetlands.
People cannot transmit the virus to each other or to mosquitoes and those that have recovered from MVEV are not likely to get infected again.
The best protection against MVEV is to prevent mosquito bites as there is no vaccine against the virus.
There is an increased risk of mosquito activity around:
- floodwater
- swamps
- wetlands
- other standing water
Protect yourself from mosquito bites by:
- wearing long-sleeved, loose-fitting, light-coloured clothing and enclosed footwear. Mosquitoes can bite through tight clothing so it is best to avoid active wear when visiting areas with increased mosquito activity
- using insect repellents that contain diethyltoluamide (DEET), picaridin or oil of lemon eucalyptus
- use insect screens on windows and doors to prevent mosquitoes from entering the home
- using mosquito coils and insecticide sprays whilst outdoors. Make sure to always follow the instructions on the product labels
- avoiding areas of high mosquito activity, if you can
Although the mosquitoes associated with MVEV are more strongly associated with floodwater and wetland environments, you should take regular action to reduce the risk of mosquitoes breeding around your home. You can do this by:
- removing standing water where mosquitoes may breed – like in plant pot basins or saucers, buckets, tyres, animal water bowls and kiddie pools
- regularly cleaning out permanent water containers – such as ponds and pet water bowls
- making sure water tank screens are in place and secure
- keeping gutters clear and lawns mowed.
