Murray Valley encephalitis virus (MVEV) is spread to humans through the bite of an infected mosquito. Most people who get infected with MVEV only have mild symptoms or no symptoms at all. However, in some cases it can cause Murray Valley encephalitis (MVE), a rare but potentially serious infection of the brain.
In early 2023, MVEV was detected in humans and mosquitoes in Victoria for the first time since 1974.
About the study
The Victorian Department of Health conducted a study between October 2023 and April 2024 across 11 local government areas (Mildura, Swan Hill, Campaspe, Greater Bendigo, Greater Shepparton, Gannawarra, Indigo, Moira, Wodonga, Wangaratta, and Loddon) aiming to determine how widespread MVEV infection has been in northern Victoria. This information will inform public health planning and prevention strategies in future mosquito seasons.
How was this study conducted?
People were invited to join the study either when they were having a routine blood test at a pathology collection centre or through community outreach. People were excluded if they had previously been diagnosed with MVE, Japanese encephalitis (JE) or Kunjin virus disease or were already vaccinated for JE. Participants completed a questionnaire and had their blood tested for evidence of prior MVEV infection.
Study findings
A total of 498 people participated in the study. Of these, 119 (24%) were recruited in the Ovens Murray region, 118 (24%) were recruited in the Goulburn Valley region, and 261 (52%) were recruited in the Loddon Mallee region. Participants were aged between 5 and 99, with a median age of 55 years. Most participants (66%) were female.
In total, 10 out of 498 (2%) participants were found to have evidence of prior MVEV infection, equal to about one in 50.
- Participants who tested positive were aged between 18 and 87 with a median average age of 69.
- Of those who tested positive, equal proportions were male and female.
- Evidence of prior MVEV infection was found in individuals living in Greater Bendigo, Campaspe, Gannawarra, Mildura, Wodonga, Wangaratta, but not in Swan Hill, Loddon, Greater Shepparton, Moira nor Indigo (Figure 1).
Figure 1: Evidence of prior MVEV infections in the recruitment LGAs
There were certain limitations to the findings of this study:
- Women and older people were overrepresented in the study compared to the general population living in the region.
- The number of participants included may not have been large enough to reliably detect risk or protective factors for MVEV infection.
Interpretation of the results
These results are preliminary. The results of the full analysis will be made publicly available at a later date.
These results suggest that only a small proportion of people living in northern Victoria have been infected with MVEV in the past. This means that many people living in the region may be at ongoing risk of MVEV infection during future mosquito seasons.
People living in or visiting northern Victoria should take steps to limit their exposure and reduce their risk of infection from mosquito bites, which can also transmit other viruses such as Japanese encephalitis virus and Ross River virus. Although there is no vaccine for MVEV or Ross River virus, there is a vaccine available to protect against Japanese encephalitis virus infection.
Further information on how you can prevent mosquito bites can be found on the Better Health .
Acknowledgements
The Victorian Department of Health would like to thank all participants who volunteered to take part in this study. We would also like to thank all collaborators involved with this study:
- Ovens Murray, Loddon Mallee and Goulburn Valley Local Public Health Units
- Victorian Infectious Diseases Reference Laboratory
- Dorevitch Pathology and Austin Pathology
- Monash University Rural Health Mildura and Bendigo
- The University of Melbourne – Rural Clinical School Shepparton
Reviewed 23 May 2024