Department of Health

Update on Japanese encephalitis virus and Murray Valley encephalitis virus in Victoria

Health alert

Status:
Active
Alert number:
230203
Date issued:
02 Feb 2023 - Update to alert issued 25 January 2023
Issued by:
Associate Professor Deborah Friedman, Deputy Chief Health Officer (Communicable Disease)
Issued to:
Health professionals and the Victorian community

Key messages

  • A second case of Japanese encephalitis (JE) virus infection has been confirmed in Victoria this mosquito season. The case spent time in Buloke Shire and Swan Hill during their acquisition period.
  • Murray Valley encephalitis (MVE) virus and West Nile (Kunjin) virus continue to be detected in mosquitoes in northern Victoria.
  • People spending time outdoors in northern Victoria are strongly recommended to take measures to prevent mosquito bites to reduce their risk of mosquito-borne disease. 
  • JE virus and MVE virus can cause a rare but potentially serious infection of the central nervous system and are spread to humans by infected mosquitoes. 
  • Symptoms may include fever, headache, nausea, vomiting and muscle aches, although most infected people do not have symptoms. In serious cases, people can develop meningitis or encephalitis.
  • Anyone with symptoms should seek urgent medical care.
  • Clinicians should test for MVE virus and JE virus in patients with a compatible illness and notify the Department of Health immediately of suspected cases by calling 1300 651 160.

What is the issue?

The risk of mosquito-borne diseases, such as MVE, JE, Kunjin/West Nile, Ross River and Barmah Forest virus infections, is high due to recent weather conditions and elevated mosquito numbers across Victoria. 

A second case of Japanese encephalitis (JE) virus infection has been confirmed in Victoria this mosquito season. The case spent time in Buloke Shire and Swan Hill during their acquisition period and likely acquired the infection in early January.

MVE virus continues to be detected in mosquitoes in northern Victoria this mosquito season. These results mean that MVE virus is circulating widely in the mosquito population and indicate a significant risk to people in these areas, particularly Mildura and northern Victoria’s inland river regions. The risk area for MVE virus is similar to that for JE virus. The risk of human cases in the coming weeks is very high and is expected to continue over the coming months. 
 

For up-to-date information on mosquito viral detections, visit the Department of Health's webpage on mosquito-borne diseases.

Who is at risk?

Anyone is potentially at risk of mosquito bites and mosquito-borne diseases. However, most mosquito bites do not transmit infection. 

People with increased exposure to mosquitoes have a higher risk of infection. These include people who work, live or spend time outdoors in northern Victoria, particularly inland riverine regions and near the Murray River. 

Symptoms and transmission

JE virus and MVE virus are spread to humans through the bite of an infected mosquito. They do not spread directly from person-to-person.
 
Most people infected with JE virus or MVE virus do not have symptoms. Less than one per cent of people develop severe disease. If symptoms develop, they typically start 1 to 2 weeks after exposure. 

Symptoms include fever, headache, nausea, vomiting and muscle aches. In rare cases, people can develop meningitis or encephalitis and have symptoms of severe headache, neck stiffness, sensitivity to bright lights, drowsiness, confusion, seizures, loss of consciousness or coma.

Serious illness can result in death or long-term neurological complications. 

People who have been exposed to JE virus or MVE virus are likely to have long-lasting immunity to subsequent infections. A Japanese encephalitis vaccine is available. See JE vaccine eligibility criteria for further details. 

Recommendations

For health professionals

Clinicians should consider JE and MVE virus infections, and other mosquito-borne diseases in patients presenting with a compatible illness, particularly in those with extensive exposure to mosquitoes or who have spent time in northern Victoria. 

MVE may be clinically indistinguishable from JE. Clinicians should test for both JE and MVE viruses in the appropriate clinical situation.

JE and MVE virus infections are urgent notifiable conditions. Clinicians and pathology services must notify the Department of Health of suspected or confirmed cases immediately by phoning 1300 651 160 (24 hours).

Recommended laboratory testing for MVE and JE virus infections includes:

  • Blood (5 to 10 mL, in a serum tube) for MVE and JE virus serology
    • Repeat convalescent serology testing at 3 to 4 weeks post onset of illness
  • Blood (5 to 10mL, in a dedicated EDTA tube) for MVE and JE virus PCR/culture
  • CSF (1 to 3mL) for MVE and JE virus serology, and PCR/culture  
  • Urine (2 to 5mL in a sterile urine jar) for MVE and JE virus PCR/culture

Samples should be sent urgently to the Victorian Infectious Diseases Reference Laboratory (VIDRL). Request forms should be appropriately labelled and the on-call pathologist at VIDRL should be contacted to provide information on samples being sent. Samples should be transported at 4 degrees Celsius.

For the public

Victorians should be aware of the risk of mosquito-borne diseases including JE and MVE virus infections. 

People with compatible symptoms should seek urgent medical care. 

The 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.
  • Use ‘knockdown’ fly sprays and plug-in repellent devices indoors.
  • 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.
  • Sleep under mosquito nets treated with insecticides if you don’t have insect screens on windows on your home or are sleeping in an untreated tent or out in the open.
  • Mosquito coils can be effective in small outdoor areas where you gather to sit or eat.

Residents and people visiting northern Victoria

In addition, residents and people visiting northern Victoria are strongly advised to take additional measures to reduce their risk of mosquito bites:

  • Wear an appropriate repellent at all times when outdoors. 
  • Avoid time spent outdoors at dusk and dawn as much as possible.

Event organisers must consider their obligations to keep event patrons safe. This requires informing patrons of the risk of mosquito exposure and the necessary protective measures, including appropriate clothing and use of repellent. Organisers may wish to postpone outdoor events or relocate them indoors during this high risk period, particularly for events scheduled around dawn and dusk.
 

Reviewed 04 February 2023

Health.vic

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Communicable Disease Prevention and Control Department of Health

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