Murray Valley encephalitis

About Murray Valley encephalitis

Murray Valley encephalitis (MVE) is a serious, but rare infection caused by the Murray Valley encephalitis virus. It is spread to humans by infected mosquitoes.

Most infected people do not have symptoms, while others may develop a mild illness and make a full recovery. A small proportion of infected people develop encephalitis, which is an inflammation (swelling) of the brain. This can potentially lead to brain damage or death.

There is no effective treatment or vaccine for MVE. The best prevention is to protect against mosquito bites.

Symptoms of Murray Valley encephalitis

Most people infected with Murray Valley encephalitis virus do not have symptoms or have only mild symptoms. A small number (about one in every 800 people) can develop severe infection.

If symptoms occur, they usually develop 7 to 12 days after being bitten by an infected mosquito, but this can be as little as 5 days or as long as 28 days.

Symptoms can include:

• fever
• nausea and vomiting
• headache
• muscle aches.

People with severe infection may develop:

• severe headaches
• neck stiffness
• sensitivity to bright light (photophobia)
• seizure or fits (especially in young children)
• drowsiness
• confusion
• loss of consciousness or coma.

Severe infection may lead to long-term brain damage or death.

Anyone with symptoms should seek urgent medical attention.

Transmission of Murray Valley encephalitis virus

People can be infected with Murray Valley encephalitis virus when they are bitten by a mosquito carrying the virus. It is not spread directly from person-to-person.

Mosquitoes pick up the virus when feeding on water birds such as herons or egrets. It is not spread to humans from contact with birds or other animals.

People who work, live or spend time outdoors in rural or regional Victoria, particularly inland riverine regions and extending up towards the Murray River, may be at increased risk of infection.

Where Murray Valley encephalitis virus usually occurs

Murray Valley encephalitis virus is found in northern Australia, where human cases are reported from time to time. Most cases occur during the wet or post-wet seasons.

In Victoria, the highest risk of MVE occurs during the summer months, especially after periods of heavy rainfall or flooding which leads to increasing numbers of water birds and mosquitoes.

Murray Valley encephalitis virus has been detected in Victoria and other south-eastern Australian states in early 2023. Human cases have been confirmed and the virus has been detected in mosquitoes.

The virus was previously detected in Victoria in 2011 from animal surveillance along the Murray River.

The last recorded human case in Victoria was in 1974, but human cases were recorded in New South Wales and South Australia in 2011.

Diagnosis of Murray Valley encephalitis

MVE can be diagnosed through testing the blood, by doing a lumbar puncture (also known as a spinal tap), and/or testing the urine.

Testing can show acute or past infection. Repeat testing is usually required to diagnose MVE.

Treatment for Murray Valley encephalitis

There is no effective treatment available for MVE. Treatment aims to support infected people and ease symptoms. Sometimes people may need hospital care.

Prevention of Murray Valley encephalitis

Your best prevention is to protect against mosquito bites:

• Cover up – wear long, loose-fitting, light-coloured clothing.
• Use mosquito repellents containing picaridin or DEET on all exposed skin.
• Limit outdoor activity if lots of mosquitoes are about.
• Remove stagnant water where mosquitoes can breed around your home or campsite.
• On holidays make sure your accommodation is fitted with mosquito netting or screens.
• Don’t forget the kids – always check the insect repellent label. On babies, you might need to spray or rub repellent on their clothes instead of their skin. Avoid applying repellent to the hands of babies or young children.

Where to get help

• Your GP (doctor)
• NURSE-ON-CALL Tel. 1300 60 60 24 – for confidential health advice from a registered nurse (24 hours, 7 days)
• Your local council – for information about mosquito control programs in your area
• Protect yourself from mosquito-borne disease

Serosurvey for Murray Valley encephalitis virus in northern Victoria

This study is about Murray Valley encephalitis virus (MVEV), which has recently been detected in humans and mosquitoes in Victoria. This is the first time MVEV has been detected in Victoria since 1974.

This work aims to understand how widespread past infection with MVEV is in regional communities in northern Victoria and which people are most likely to become infected. This information will help to inform our public health planning and prevention strategies.

Participants

This study aims to identify what proportion of people (of any age) living in the Local Government Areas of Mildura, Swan Hill, Campaspe, Greater Bendigo, Greater Shepparton, Gannawarra, Indigo, Moira, Wodonga, Wangaratta and Loddon have been previously infected with MVEV.

Participants must not have been:

1. Previously vaccinated for Japanese encephalitis
2. Previously diagnosed with or tested positive for (including on blood tests which detect past infection) Murray Valley encephalitis, Japanese encephalitis, or Kunjin virus infection.

Over a 6 month period, more than 500 people came forward to help us understand how widespread past infection with MVEV is in northern Victoria. This information will help to inform our public health planning and prevention strategies.

The study's results will be made publicly available once the analysis is complete.

To find out more please contact the Victorian Department of Health's MVEV serosurvey team via email at cdir@health.vic.gov.au.