Japanese encephalitis virus (JEV) is an infection that is spread to humans through the bite of an infected mosquito. Most people who get infected with JEV have mild symptoms or no symptoms at all. However, JEV can cause Japanese encephalitis (JE), a rare but potentially serious infection of the brain.
About the study
In early 2022, JEV was detected in humans, pigs, and mosquitoes in Victoria for the first time. This study aimed to help us understand how widespread JEV infection is in northern Victoria and which people are most likely to become infected. This information informs our public health planning and prevention strategies.
How was this study conducted
People were asked to join the study either when they were having a routine blood test at a pathology collection centre (see Figure 1), through community outreach, or after a household member tested positive in the serosurvey. People were excluded if they had previously been diagnosed with or were already vaccinated for JE or were born in a JEV endemic country.
Figure 1: Primary recruitment locations
All participants completed a questionnaire and had their blood tested for evidence of prior JEV infection. Blood testing was performed at a reference laboratory in Victoria and sent to another laboratory in New South Wales for confirmation.
Findings of the study
Who participated
A total of 820 people completed a questionnaire and provided a blood sample for this study. Of these, 561 (68%) were recruited in the Ovens Murray region, 195 (24%) were recruited in the Goulburn Valley region, and 64 (8%) were recruited in the Loddon Mallee region. Participants were aged between 7 and 92, with a median age of 59 years. The majority of participants (61%) were female.
Results
In total, 27 out of 820 (3.3%) participants were found to have evidence of prior JEV infection, equal to about one in thirty.
- Participants who tested positive were aged between 25 and 90 with a median average age of 73.
- A majority of those who tested positive were male (14/27, 52%).
- Participants who had evidence of prior JEV infection were found in all three regions (Figure 1).
Limitations
- These results are an estimate only. Participation in this study was voluntary and this may have influenced those who participated in the study. The proportion of people who tested positive was different in different areas (higher or lower than the overall estimate). In some areas, only a small number of participants were recruited which may have influenced the overall estimate.
- The results may be biased (too low or too high) if the participants recruited to the study were not representative of the population living, working, or visiting these areas. For example, our sample was a predominantly female and older population, which may have influenced the results.
Next steps
These results are preliminary. The results of the full analysis will be made publicly available at a later date.
These results suggest that people living in or visiting northern Victoria may be at risk of JEV infection and should take steps to limit their exposure to mosquitoes during peak mosquito season in the warmer months, from October to March. Mosquitoes can also transmit other viruses such as Ross River virus, Barmah Forest virus, Murray Valley encephalitis virus or Kunjin virus. A vaccine is available to protect against JEV infection.
See information on how to protect yourself and others against mosquito-borne .
Key participants in the study
The Department of Health would like to thank all participants who volunteered to be part of this study. We also acknowledge and thank all investigators and collaborators involved with this study:
- Ovens Murray and Goulburn Valley Public Health Units
- Victorian Infectious Diseases Reference Laboratory and Institute of Clinical and Medical Pathology in New South Wales
- Dorevitch Pathology and Austin Pathology
- Monash University Rural Health Mildura
- The National Centre for Immunisation Research and Surveillance
Reviewed 01 March 2023