Murray Valley encephalitis virus infection

At a glance

No vaccine available – read more about prevention
Nationally notifiable disease

About Murray Valley encephalitis

MVE is a rare but serious infection of the brain and spinal cord.

It is caused by the MVE virus, which is spread by certain types of mosquitoes.

Why it matters to public health

For many people, MVE virus infection causes no symptoms or mild symptoms. Symptoms might appear general at first in those who get them but can progress to become very serious.

Up to 1 in 3 people who develop encephalitis die from the disease. Of those who do survive, up to half develop long-term neurological issues.

There is no vaccine or specific treatment.

The main type of mosquito that carries MVE virus can be found across Australia. The virus is present in mosquitoes in northern Australia and sometimes spreads to south-eastern Australia.

Outbreaks happen infrequently but are always serious.

Because of these major impacts, we:

work with colleagues in the animal and environmental sectors at the national and state and territory levels to ensure a One Health coordinated approach to monitoring and reporting on MVE
plan for how to manage outbreaks.

Symptoms

If you’re looking for advice about your own health or treatment options, see healthdirect or speak with a qualified healthcare professional. Our role is to provide public health advice – information and guidance that helps prevent disease, protect communities and improve wellbeing at a population level.

Common, mild symptoms can include:

Less than 0.5% of people who are infected develop serious illness, including:

brain inflammation (encephalitis)
inflammation of the lining of the brain and the spinal cord (meningitis).

In children, about 1 in 20 may develop serious illness.

Symptoms of encephalitis and meningitis include:

drowsiness
confusion
tremor
neck stiffness
seizures
coma
irritability (for babies who are infected).

healthdirect’s symptom checker can help you decide whether to see a health professional.

Check your symptoms

Onset of symptoms

Symptoms usually start between 7 and 12 days after an infected mosquito bite, but this can range from 5 to 28 days.

How it spreads

MVE virus is spread through bites of certain types of mosquitoes after they have fed on infected waterbirds.

The type of mosquitoes that spread MVE virus are found throughout Australia and in Papua New Guinea.

These mosquitoes are usually active:

from mid-spring to late autumn in south-eastern Australia
all year in northern Australia.

Mosquito activity is more likely after heavy rainfall and flooding, or around wetlands.

People who have recovered from MVE virus are not likely to get infected again.

Infectious period

People cannot transmit the virus to each other or to mosquitoes.

Prevention

There is no vaccine against MVE virus infection.

The best protection against MVE virus is to prevent mosquito bites.

Priority groups and settings

Some people are at greater risk of getting MVE or getting very sick from it.

If you are at increased risk of being exposed to MVE virus, it is especially important to take steps to protect yourself from mosquitoes.

People at greater risk of severe disease

Everyone is at risk of developing serious disease after MVE virus infection.

But the risk of severe illness is greater for:

infants and young children
people aged 50 years or older
people who are immunocompromised.

People at greater risk of exposure

People are at increased risk of being exposed to MVE if they:

work or spend a lot of time outdoors
live or work near wetlands or rivers
live in or travel to areas where the virus has been detected – especially northern Australia or Papua New Guinea.

Diagnosis and treatment

MVE virus infection diagnosis usually requires:

a blood test
assessment of symptoms
review of recent travel history and exposure to mosquitoes.

Spinal fluid (lumbar puncture) and urine tests are sometimes required to diagnose MVE virus infection.

You can use healthdirect’s directory to find a health service near you.

Find a health service

There is no specific treatment for MVE virus infection.

If you have severe symptoms, you will likely need to be cared for in hospital.

Surveillance and reporting

MVE virus infection is a nationally notifiable disease – these are diseases that present a risk to public health.

Health authorities in each state and territory report laboratory confirmed and probable cases to us daily through the National Notifiable Diseases Surveillance System.

This is part of our surveillance activities, which help us monitor case numbers around the country and understand disease patterns.

We take a One Health approach to surveillance of MVE virus. As well as human disease surveillance, we work with other government departments to monitor MVE virus in mosquitoes and animals, including wildlife and the environment.

We analyse the data and report on case numbers and other data through our data visualisation tool, where you can filter and search the latest information.

Outbreaks

In areas where cases are not normally reported, one case of MVE virus infection may be considered an outbreak. In other areas, an increase in cases or a cluster of cases might trigger an outbreak response.

Control measures used during outbreaks focus on humans, animals and the environment, and include:

animal surveillance to track the virus
mosquito control activities
communication to health professionals to increase awareness of MVE and its signs and symptoms
making sure that personal mosquito control items are available, including in local shops
mosquito bite prevention education and promotion.

Read more about how the Australian Government defines and plans for outbreaks.

Support

For information about MVE in your state or territory, see:

If you need mental health support, see a list of organisations, websites and services that offer support, counselling and information.

For travel advice, see Smartraveller.