Murray Valley Encephalitis Confirmed in NSW: First of Season

A Murray Valley encephalitis (MVE) virus infection has been identified in the Riverina, the first NSW case of this mosquito season and the first confirmed transmission of the virus in the state since 2011.

The case is in a man in his 60s, who was potentially exposed to infected mosquitoes in the Temora Shire, Edward River Shire or Murrumbidgee Council areas, which are areas of MVE concern. The infection was likely acquired in January 2023. The man has been admitted to hospital, where he continues to receive treatment.

Keira Glasgow, Director of NSW Health's One Health branch, said the case follows recent MVE detections in mosquitoes and sentinel chickens in parts of western and southern NSW where surveillance is being carried out.

"There is no vaccination or specific treatment for Murray Valley encephalitis, so we urge the community to do everything they can to protect themselves against mosquito bites," Ms Glasgow said. 

"The best way to avoid infection is to avoid being bitten by mosquitoes, which are most active between dusk and dawn. Avoiding mosquito bites will also protect against other mosquito-borne infections including Japanese encephalitis, Kunjin and Barmah Forest viruses.

"Only a small proportion of people infected with the virus will have any symptoms, which include fever, headache, nausea, vomiting, loss of appetite, diarrhoea, and muscle aches.

"Signs of severe infection include severe headache, neck stiffness, sensitivity to bright lights, drowsiness, confusion, seizures, and loss of consciousness."

Ms Glasgow said that the number of MVE detections in mosquitoes and sentinel chickens this season was concerning. In response, NSW Health has established an expert advisory panel on mosquito control and management with medical entomologists from across Australia.

"We are looking closely at the various approaches to mosquito control in different environments and in areas with different population densities to help inform our approach to mosquito control and management in NSW," Ms Glasgow said.

MVE virus is spread to humans by infected mosquitoes. Rarely, it causes severe neurological illness. The primary hosts of MVE and Japanese encephalitis virus (JEV) are wild waterbirds such as herons and egrets.

Protect yourself and your family from mosquito bites by:

  • wearing light, loose-fitting long-sleeved shirts, long pants and covered footwear and socks, especially around dusk and dawn
  • applying repellent to all areas of exposed skin, using repellents that contain DEET, picaridin, or oil of lemon eucalyptus
  • re-applying repellent regularly, particularly after swimming, being sure to always apply sunscreen first and then apply repellent
  • covering openings such as windows and doors with insect screens and checking there are no gaps in them
  • removing items that might collect water (such as old tyres, empty pots) outside your house where mosquitoes can breed
  • improving drainage on your property so that water does not become stagnant
  • using insecticide sprays, vapour dispensing units and mosquito coils to repel mosquitos (mosquito coils should only be used outside).

For further information and ways to protect yourself visit Mosquito-borne diseases.

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