About Murray Valley encephalitis
Murray Valley encephalitis (MVE) is a serious, but rare infection caused by Murray Valley encephalitis virus. Most people don’t have any symptoms, while others may develop a mild illness and make a full recovery. A small proportion of people infected develop encephalitis, which is an inflammation (swelling) of the brain tissue. This can lead to brain damage or death.
Murray Valley encephalitis virus is caused by a flavivirus, which is spread by mosquitoes. Symptoms usually begin to appear between 7 to 12 days after becoming infected. But this can be as little as 5 days or as long as 28 days.
When in mosquito-prone areas, wear long, loose-fitting, light coloured clothing and use insect repellent containing DEET or Picaridin to help reduce the chance of being bitten by mosquitoes.
Symptoms of Murray Valley encephalitis virus
Most people who get Murray Valley encephalitis virus show no symptoms.
If symptoms occur, they can include:
nausea and vomiting
If symptoms of encephalitis occur, please seek medical attention immediately. These symptoms include:
sensitivity to bright light (photophobia)
seizure or fits (especially in young children)
Mosquitoes spread Murray Valley encephalitis virus
People can be infected with Murray Valley encephalitis virus when they are bitten by a mosquito carrying the virus. Culex annulirostris (the common banded mosquito) is the most important mosquito species that carries this virus. This mosquito is widespread throughout Australia, breeds in fresh water and is most active at dusk and dawn. Mosquitoes can pick up the virus when feeding on water birds such as herons or egrets. Diseases that are spread by insects are known as ‘vector-borne’ diseases.
There is no evidence that Murray Valley encephalitis virus can be spread directly from one person to another. This virus cannot be caught directly from contact with birds or other animals.
Where Murray Valley encephalitis virus usually occurs
Murray Valley encephalitis virus is native to and always present in northern Australia, where human cases are reported from time to time, mostly during the wet or post-wet seasons.
In Victoria, the biggest risk for Murray Valley encephalitis virus occurs during the summer months – especially after periods of heavy rainfall or flooding, as this leads to increases in water birds and ideal breeding conditions for mosquitoes. The last recorded human cases occurred in 1974, however the virus was detected in chickens located along the Murray River in 2008 and again in 2011.
Diagnosis of Murray Valley encephalitis virus
Blood tests can reveal if a person has been infected with Murray Valley encephalitis virus recently or in the past. A lumbar puncture (also known as a spinal tap) may be done in people who have encephalitic symptoms.
Treatment for Murray Valley encephalitis virus
There is no specific treatment available for Murray Valley encephalitis virus. Treatment aims to support the patient and ease the symptoms while their body fights the virus. Your doctor will decide with you what treatment is best suited to your situation. Sometimes people may need hospital care, depending on the severity of the infection and if complications develop.
The severity of Murray Valley encephalitis infection can vary from person to person. Generally, the acute phase of the illness lasts around 1 or 2 weeks, and the symptoms either disappear quickly or subside slowly over a period of time. In many cases, the person makes a full recovery. In other cases, the person can be left with varying degrees of brain damage, which may require long-term supportive care and therapy.
Preventing Murray Valley encephalitis virus
There is no preventive vaccine available. Your only protection against Murray Valley encephalitis virus is to avoid mosquito bites.
To reduce the risk of infection:
Wear long, loose-fitting, light-coloured clothing and use insect repellents that contain DEET or Picaridin applied regularly, according to the manufacturer’s instructions.
Avoid mosquito-prone areas, especially at dusk and dawn when mosquitoes are more active and likely to bite.
Ensure that your accommodation has fly screens properly fitted to windows and external doors.
Reduce the number of potential mosquito breeding habitats around your home by ensuring no stagnant water is present. Containers holding water should be emptied and washed regularly
Where to get help
This page has been produced in consultation with and approved by:
Department of Health and Human Services - RHP&R - Health Protection - Communicable Disease Prevention and Control Unit
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