Buruli ulcer (also known as Bairnsdale ulcer) is an infection of skin and soft tissue caused by the bacterium Mycobacterium ulcerans. The toxin made by the bacteria attacks fat cells under the skin, which leads to localised redness and swelling or the formation of a nodule (lump) and then an ulcer.
Although Buruli ulcer is not fatal, the infection can often leave people with significant cosmetic, and sometimes functional, damage to limbs.
Cases of Buruli ulcer have increased significantly in Victoria in recent years, particularly along the Mornington and Bellarine peninsulas, and the disease is spreading into new geographical areas. Over the past few years, Victorian scientists have been conducting intensive research in a search for answers around the puzzling aspects of this condition. Although it's understood that the infection is picked up from the environment, it's not yet known exactly how humans become infected with the bacteria, or where in the environment the bacteria prefer to live. It is not thought to be spread person-to-person.
The Beating Buruli in Victoria research project
The ‘Beating Buruli in Victoria’ research project was launched in 2018, with funding from the National Health and Medical Research Council (NHMRC) and the Victorian Department of Health. It is a multidisciplinary and collaborative partnership between the Department of Health, Doherty Institute, University of Melbourne, Barwon Health, Austin Health, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Agriculture Victoria and the Mornington Peninsula Shire Council.
By identifying more precisely when and where Buruli ulcer transmission occurs, including the specific mosquito and possum species involved, and testing methods of mosquito control targeting the places and times of highest risk, this project hopes to actively disrupt Buruli ulcer transmission for the first time. It is hoped these findings will lead to the development of evidence-based policies and guidelines that can help reduce and prevent cases of Buruli ulcer in Victoria and perhaps globally.
Ongoing research 2022 - 2023
- Mosquito lab work: The mosquitoes that were collected during previous research activities are being processed to determine how many of them were carrying M. ulcerans. By identifying geographic areas where mosquitoes carrying M. ulcerans are, we can focus our interventions in these higher-risk areas. We are also undertaking sophisticated mosquito genomic modelling to see how far mosquito populations are travelling and spreading M. ulcerans.
- Possum faecal (excreta) surveys are continuing across Melbourne, Greater Geelong and the Mornington and Bellarine Peninsulas. Field staff collect possum excreta that are screened for M. ulcerans in the lab. This identifies geographic areas in which the bacteria are being actively shed into the environment by infected possums.
- Possum surveillance studies involve monitoring free-ranging possums in parts of Victoria where Buruli ulcer is known to occur. Revisiting these locations at regular intervals will allow long-term monitoring of the progression of Buruli ulcer disease in possums and its impacts on animal welfare.
- A field trial of a new mosquito trap that has direct and knock-on effects on mosquito populations is proposed for the Mornington Peninsula in early 2023, if permits can be secured for their use. Preliminary trials have shown these traps are effective at reducing populations of Aedes notoscriptus, the mosquitoes that transmit Buruli ulcer.
Data from these research activities, as well as human Buruli ulcer case data, are being used to predict locations and times of greatest Buruli ulcer transmission risk in Victoria, using a geospatial computer modelling program created by the project team. This will inform the design and delivery of targeted public health interventions to prevent human cases of Buruli ulcer in Victoria.
The ‘Beating Buruli in Victoria’ team would like to thank the community for the support received during our research and intervention activities to date. The team looks forward to continuing to work with local communities in areas affected by Buruli ulcer towards stopping the spread in Victoria.
If you have any questions about this research, please email the project team at beating-buruli@unimelb.edu.au
Completed studies under the ‘Beating Buruli in Victoria’ project (2018–2022)
Mosquito surveillance and control studies
Mosquito surveillance conducted on the Mornington Peninsula captured over 60,000 mosquitoes during a four-month period (November 2019 – March 2020). This showed that there are three dominant species of mosquito in the region that accounted for 86% of all mosquitoes: Culex molestus (42%), Aedes (Ae.) notoscriptus (37%), and Culex australicus (7%).
Research has shown:
- Only Ae. notoscriptus has consistently tested positive in the laboratory for M. ulcerans, indicating that mosquito control activities need to focus on this species (see Figure 1).
- The Ae. notoscriptus species fly much greater distances than was previously thought, which has implications for mosquito control activities. These findings are available as a pre-print here: https://www.biorxiv.org/content/10.1101/2022.01.18.476837v2.
Given these results, the project team have undertaken a series of mosquito control studies, using the hypothesis that reducing mosquito numbers will result in fewer Buruli ulcer cases in the study areas.
Mornington Penninsula
|
Study period |
Study size |
Methods used |
Results |
Comments |
|
March 2019 |
3 residential streets |
Residual spraying of pyrethroid insecticides |
Reduced mosquito numbers |
Local government and some residents objected to insecticide spraying, leading the project team to abandon this approach |
|
February – April 2021 |
Approximately 700 properties, grouped into 10 zones (five intervention and five control zones) |
Combination of mosquito trapping, mosquito breeding source reduction and community education |
Did not reduce mosquito numbers |
Intermittently occupied holiday houses in study areas contributed to low intervention uptake and acted as ‘hotspots’ for mosquito breeding |
|
February – April 2022 |
Approximately 25 individual properties |
Combination of mosquito trapping and mosquito breeding source reduction |
Did not reduce mosquito numbers |
Recent research findings showed that Ae. notoscriptus fly much greater distances than previously thought, which would have affected the success of this trial |
Outer Melbourne
|
Study period |
Study size |
Methods used |
Results |
Comments |
|
Early 2022 |
Approximately 5 hectares |
New ‘In2Care’ traps that have direct and knock-on effects on mosquito populations |
Reduced mosquito numbers |
Given the success of this trial, a larger study is planned in 2023 (subject to permit approval) |
Possum excreta surveys, 2018–2022
While the transmission cycle of Buruli ulcer in Victoria is not yet fully understood, there is increasing evidence that mosquitoes and possums play a role in disease transmission. Native possums are known to shed large numbers of M. ulcerans in their faeces.
Figure: While some aspects of Buruli ulcer transmission in Victoria are not fully understood, there is increasing evidence that mosquitoes and possums play a role in a disease transmission.
Possum excreta surveys, in which project field staff collect possum faecal pellets from predetermined sampling locations at 200 metre intervals, have been conducted in Victoria since November 2018. Survey locations have included the Mornington Peninsula, Melbourne and Bayside suburbs, Greater Geelong and the Bellarine Peninsula.
The possum faecal pellets are then tested for M. ulcerans using a laboratory test that detects DNA, as only a small amount of DNA is required to perform the test. This cost effective and relatively easy testing method allows us to identify areas where possums are excreting the M. ulcerans bacteria into the environment, enabling the application of targeted mosquito control activities that might be most beneficial to protect people from Buruli ulcer. The findings of this research are available as a pre-print here: https://www.biorxiv.org/content/10.1101/2022.11.16.516821v1?rss=1.
Case-control and environmental field survey study, 2018-2020
Barwon Health and the CSIRO led this research, with support from the Department of Health, Mornington Peninsula Shire Council, Deakin University, the Doherty Institute, and Agriculture Victoria.
256 Victorians with Buruli ulcer (‘cases’) and 458 without ('controls') participated by completing a study questionnaire in 2018–2020. Field surveys were conducted at the properties of 230 study participants, which involved the collection and testing of multiple environmental samples for the presence of M. ulcerans.
The case control and environmental field survey study results identified several factors associated with an increased risk of a person getting Buruli ulcer (i.e. risk factors), and factors associated with a reduced risk of getting the disease (i.e. protective factors):
- Factors that reduce risk of getting Buruli ulcer include: using insect repellent, wearing long sleeves when outdoors, and immediately tending to wounds.
- Factors that can increase the risk for Buruli ulcer include: a property with possums, ponds and certain types of native plants; having an outdoor job (especially one with regular soil contact); and using bore water for bathing or gardening,
Detailed results of the environmental field survey are available here: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0274627.
