Two deaths from Murray Valley encephalitis have been confirmed in Alice Springs, prompting a renewed health alert from the Northern Territory Department of Health.
The fatalities occurred in April and May 2025. Health authorities have not released further details about the victims. The virus was also detected in mosquitoes in Darwin earlier in May.
Disease Background
Murray Valley encephalitis (MVE) is a rare disease transmitted by the bite of an infected mosquito, primarily the Culex annulirostris species. The virus is most commonly detected in northern Australia, particularly the Kimberley region of Western Australia and the Top End of the Northern Territory.
Most people infected with the virus do not develop symptoms. Among those who do, approximately 25% die, and 40% do not fully recover. There is no vaccine or specific treatment for the virus; prevention relies entirely on avoiding mosquito bites.
Transmission Season and Risk Areas
The virus is most frequently transmitted in the Northern Territory between February and July, with the peak period occurring from March to May.
Following significant rainfall, high mosquito numbers have expanded the risk area to include the entire Northern Territory. The disease is most common in the Top End and Barkly regions.
- Northern regions: Mosquito numbers are expected to remain high in the Top End, Big Rivers, Greater Darwin, and East Arnhem regions until the end of July.
- Central regions: In Central Australia and the Barkly regions, numbers are expected to decrease due to cold overnight temperatures.
- Southern regions: Under favorable conditions, such as increased rainfall and flooding often associated with La Niña, the virus can emerge further south.
Symptoms
Symptoms of Murray Valley encephalitis include:
- Severe headache
- Fever
- Nausea
- Vomiting
- Muscle aches
- Drowsiness
- Confusion
- Seizures
Prevention
Health authorities recommend the following measures to prevent mosquito bites:
- Use insect repellents containing DEET, picaridin, or oil of lemon eucalyptus
- Wear light-colored, long-sleeved shirts, long pants, and covered shoes when outdoors
- Ensure tents are mosquito-proof when camping
- Protect infants and children with appropriate clothing and mosquito nets
- Avoid areas prone to mosquitoes, particularly after sundown
- Use mosquito coils or lanterns outdoors
Historical Context
Since surveillance began in 1978, 48 cases of Murray Valley encephalitis have been recorded in the Northern Territory, including the two deaths in 2025.
Notable previous outbreaks include:
- 1974: 58 cases and 12 deaths
- 2011: 17 cases
- 2023: 26 cases, including two deaths and two cases resulting in severe neurological impairment
Comparison with Japanese Encephalitis
Murray Valley encephalitis virus and Japanese encephalitis virus (JEV) are closely related but distinct. A vaccine exists for Japanese encephalitis but not for Murray Valley encephalitis.
A 2022 outbreak of Japanese encephalitis in southeastern Australia led to over 40 cases and 7 deaths. Scientists are investigating whether the Japanese encephalitis vaccine may provide protection against Murray Valley encephalitis, but research is ongoing.