Murray Valley Encephalitis (MVE)

Last updated: 31 January 2008

What is MVE?

Murray Valley encephalitis (MVE) is a mosquito-borne disease caused by the Murray Valley encephalitis virus. It is also known as Australian encephalitis.
MVE usually occurs in remote north western Australia. It rarely occurs in eastern Australia. To date there have been no human cases in south eastern Australia (including NSW and Victoria) reported since 1974. In previous outbreaks the virus affected people living in western NSW.

What are the symptoms?

The disease takes about 5 to 15 days (normally 7 to 12 days) between getting bitten and becoming sick. The majority of people infected with MVE will have no symptoms.
Of those who do, symptoms include:

• high fever
• severe headache
• seizures or fits (especially in young children)
• tremors
• neck stiffness
• lethargy, irritability, drowsiness
• vomiting
• nausea
• diarrhoea
• dizziness
• confusion
• coma in severe cases.

How is it spread?

• The MVE virus is spread by the bite of an infected mosquito (usually Culex annulirostris also known as the "common banded" mosquito).
• Not all of these mosquitoes carry the virus, and only about 1 person in a 1000 who get bitten by infected mosquitoes will become unwell.
• The virus is thought to be mainly carried by water birds. Mosquitoes become infected by biting birds or other animals that carry the virus. Spread to south eastern Australia is thought to occur with water bird migration that follows unusually wet conditions in inland Australia.

Who is at risk?

People most at risk are babies, young children and newcomers to the region. The disease is fatal in about 20 per cent of those who become sick, and a further 25 per cent can develop major neurological complications. About 40 per cent of cases will make a complete recovery.

How is it prevented?

There is no specific treatment or vaccine available for MVE. The only protection from MVE is to avoid being bitten by mosquitoes. This is particularly important to travellers and visitors to areas where MVE might be active.

Mosquito protection during periods of MVE activity is absolutely essential:

• Avoid being outside when mosquitoes are most active, particularly in the morning and from just before sunset to mid-evening.
• Wear looose fitting light coloured clothing with long sleeves, long trousers and socks. Mosquitoes can bite through tight fitting clothes.
• Use insect repellent when outdoors and reapply as directed by the manufacturer. Lotions and gels are more effective and longer lasting than sprays.
• Make sure flyscreens and doors are in good order.
• If camping out, sleep under a mosquito net or in a mosquito-proof tent.
• Use a knock down insect spray before going to bed to kill any mosquitoes that are indoors.

How is it diagnosed?

MVE is diagnosed when a blood test or test of the spinal fluid shows evidence of the virus (through nucleic acid testing or a rise in antibodies).

How is it treated?

Patients with MVE will usually require extensive support. There is no specific treatment for MVE.

What is the public health response?

MVE activity in birds is monitored through a network of sentinel chicken flocks in western NSW. Laboratories are required to notify cases of MVE to the local public health unit. Public health unit staff will interview the cases (or carer) to identify risk factors. A single report will usually lead to a search for other possible cases and further advice to the local community.