Reporting week: 23/04/2023 to 29/04/2023
Report issued date: 15 May 2023
Note: This is the last report for the 2022-23 mosquito season.
Every year, the department conducts mosquito surveillance throughout the Victorian mosquito breeding season. In inland areas, the mosquito season typically starts from early November through to late April the following year, while in coastal areas it typically starts earlier and ends later.
The report contains a range of indicators relating to mosquito-borne diseases actively monitored by the department. The indicators used in these reports are sourced from the following surveillance systems:
- Human surveillance (notified confirmed and probable cases and/or modelled predictions of vector-borne disease)
- Mosquito surveillance (adult mosquitoes)
The report contains information collected in the week prior and there can be a time delay from mosquito field collection to reporting.
Human cases of mosquito-borne diseases
In 2022/2023 there have been five mosquito-borne viruses identified to pose public health risk in Victoria with the potential for local transmission. These are Japanese encephalitis virus (JEV), Murray Valley encephalitis virus (MVEV), Ross River virus (RRV) and Barmah Forest virus (BFV), West Nile virus Kunjin strain (WNV/Kunjin) (otherwise known as Kunjin virus).
Cases of infection with these viruses are notified to the department by pathology services and in some cases medical practitioners under the Victorian Public Health and Wellbeing Regulations 2019. The laboratory diagnosis of mosquito-borne diseases is complex, and often requires follow up testing at several weeks before the confirmed or probable case definition is met.
RRV and BFV are endemic to parts of Victoria, and cases of infection with these viruses are expected every summer. The department closely monitors case numbers and geographical distribution to identify areas of increased risk.
The bar charts below show monthly confirmed and probably cases of mosquito-borne diseases. Hover over each bar to see the number of cases.
Japanese encephalitis virus
There were no cases of JEV infection reported in this reporting period.
Japanese encephalitis virus infection epidemic curve - monthly confirmed and probable cases
Murray Valley encephalitis virus
There were no cases of MVEV infection reported in this reporting period. A sixth case of MVEV infection first notified in April 2023 has been confirmed since the last report.
Murray Valley encephalitis virus infection epidemic curve - monthly confirmed and probable cases
Ross River virus
Ross River virus infection epidemic curve - monthly confirmed and probable cases
Currently, approximately 15 councils in high-risk areas for mosquito-borne diseases participate in the state-wide mosquito surveillance program. Mosquitoes trapped as part of this program are submitted to the Agriculture Victoria Research laboratory at the Department of Energy, Environment and Climate Action (DEECA) for mosquito species identification, counting and viral testing. These data are then reported to the department for monitoring and analysis.
Mosquito viral detections map
The interactive map below shows mosquito-borne virus detections in trapped mosquitoes across Victoria. Each mosquito-borne virus has been given its own colour. You can search the map by mosquito-borne virus using the radio buttons.
At each Local Government Area (LGA), you can click to find out which viruses were detected at these LGAs and when.
Average number of mosquitoes per trap site per week by Local Government Area (LGA)
|Extreme (10,000+)||Very high (1,000 - 9,999)|
|High (100-99)||Moderate (50-99)|
Mosquito species of concern
In inland areas Culex annulirostris is considered the major species of concern for transmission of RRV, BFV, WNV/Kunjin, and MVEV. It is also believed to be a major vector for JEV.
Aedes camptorhynchus is the major vector of RRV and BFV in coastal saltwater habitats.
A sample of trapped mosquitoes are examined to estimate the proportion of different species. The availability and accuracy of this representative sample is influenced by the number of mosquitoes captured, the condition of the mosquitoes at time of examination, and other factors.
The charts below show the proportion of trapped adult mosquitoes by species in North West Victoria, North Central & East Victoria, Gippsland, and South West Victoria.
Proportion of trapped adult mosquitoes by species - North West Victoria (Buloke, Mildura, Northern Grampians, Swan Hill, Gannawarra, Loddon and Horsham)
Proportion of trapped adult mosquitoes by species - North Central & East Victoria (Campaspe, Greater Bendigo, Greater Shepparton, Macedon Ranges, Mitchell, Indigo, Moira, Wangaratta and Wodonga)
Proportion of trapped adult mosquitoes by species - Gippsland (East Gippsland and Wellington)
Proportion of trapped adult mosquitoes by species - South West Victoria (Surf Coast and Greater Geelong)
Reviewed 19 May 2023