Murray Valley encephalitis - including symptoms, treatment and prevention

Murray Valley encephalitis (MVE) is a rare disease in humans caused by the Murray Valley encephalitis virus. 

MVE virus is endemic (always present) in northern Australia (northern Western Australia and the top end of the Northern Territory) and probably in Papua New Guinea, but illness in humans is rare.

Most reported human cases occur in northern Australia and Papua New Guinea, although there have been rare cases fom South Australia.

Murray Valley encephalitis (MVE) is a notifiable condition1

How Murray Valley encephalitis is spread

Murray Valley encephalitis is transmitted to humans through the bite of infected Culex mosquitoes, which acquire the virus from infected water birds such as herons and egrets that act as reservoir hosts. 

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.

There is no direct person-to-person spread

Signs and symptoms of Murray Valley encephalitis

Many people infected with Murray Valley encephalitis virus have no symptoms or mild symptoms. Symptoms of Murray Valley encephalitis include:

  • fever
  • drowsiness (excessive sleepiness)
  • confusion
  • headache
  • nausea and vomiting
  • tremors
  • additionally in infants, irritability and floppiness.
  • neck stiffness and intolerance of bright light, indicating progression to meningitis (inflammation of the lining of the brain and spinal cord) or encephalitis (infection or inflammation of the brain). This can progress to seizures, coma and death.

Among those who get a severe infection, some may have lifelong neurological complications or death.

Diagnosis of Murray Valley encephalitis

Diagnosis is made by a blood test or detecting the virus in CSF (cerebrospinal fluid: the fluid surrounding the brain and spinal cord, collected by a spinal tap procedure).

Incubation period

(time between becoming infected and developing symptoms)

Usually 7 to 12 days, but can be as short as 5 days or as long as 28 days.

Infectious period

(time during which an infected person can infect others)

There is no evidence of person-to-person transmission. A person is immune for life after an infection with Murray Valley encephalitis virus.

Treatment for Murray Valley encephalitis

There is no specific treatment for Murray Valley encephalitis.

People who are diagnosed with Murray Valley encephalitis are usually very sick and require supportive care in hospital until they recover.

Prevention of Murray Valley encephalitis

  • Exclusion from childcare, preschool, school or work is not necessary but cases should avoid being bitten by mosquitoes while they are unwell.
  • There is no vaccine to prevent human infection by this virus.
  • Personal protection and the environmental management of mosquitoes are important in preventing illness. For more information, see Mozzies Suck.

Useful links

1 – In South Australia the law requires doctors and laboratories to report some infections or diseases to SA Health. These infections or diseases are commonly referred to as 'notifiable conditions'.