- A new mosquito control trial will be taking place on the Mornington Peninsula over summer 2022.
- 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.
- The disease is not spread person-to-person.
- Native Australian possums can be victims of Buruli ulcer too.
- Research has shown that areas where humans are most frequently contracting Buruli ulcer are areas where mosquitoes and possums are most frequently carrying the causative bacteria.
- A new three-year research project commenced in February 2021 through a collaborative partnership between the Victorian Department of Health, the Doherty Institute, Barwon Health, Austin Health, Agriculture Victoria, the University of Melbourne and the Mornington Peninsula Shire, aiming to better understand how Buruli ulcer is transmitted and determine effective ways to reduce and prevent infections.
- The 'Beating Buruli in Victoria' project hopes to actively disrupt disease transmission for the first time and lead to the development of evidence-based policies and guidelines that can help stop the spread of Buruli ulcer around Victoria and even globally.
Beating Buruli research project updates
The hunt for answers to Beat Buruli In Victoria continues.
Project updates 2021, and plans for 2022
- A combination of mosquito trapping and source reduction interventions were trialled on the Mornington Peninsula during early 2021.
- The revised study design was supported by the study communities and local government.
- Unfortunately, the trial did not show a reduction in mosquito numbers in the intervention zones compared to the control zones.
- This result could have been due to a range of factors, including the presence of many intermittently occupied holiday homes that contributed to low intervention uptake, and which can act as ‘hotspots’ for mosquito breeding.
- A new intervention for summer 2022 is being planned that will invite Mornington Peninsula residents to participate in mosquito reduction activities on their properties. This intervention will occur at a single property level compared to the street level intervention trialled the previous summer.
- Other project activities are also underway, including possum scat (faecal) surveys, mosquito screening and testing, and possum surveillance studies.
Results of surveillance surveys, 2018-2020
Field surveys were conducted throughout the Mornington Peninsula during the summer months of 2018/2019 and 2019/2020, when peak transmission of Buruli ulcer is known to occur.
- Possum faecal surveys were conducted between November 2018 and March 2019, with teams of intrepid field staff collecting more than 2,000 possum faecal pellets at 200 metre intervals in a grid format, spanning the region between Portsea, Rosebud and St Andrews
- From weekly visits between November 2019 and March 2020, more than 50,000 mosquitoes were trapped across the same region from 180 defined sites.
The collected possum excreta and mosquitoes were screened by a sensitive laboratory test for the presence of Mycobacterium ulcerans, the bacteria responsible for causing Buruli ulcer.
The interim results from both the possum faecal survey and the mosquito survey were mapped to the Mornington Peninsula region to show those areas where possums and mosquitoes were most commonly harbouring M. ulcerans.
These data revealed a very strong association between areas where possum excreta and mosquitoes are positive for M. ulcerans, and cases of Buruli ulcer in humans. This allows us to identify areas that are likely areas of Buruli ulcer transmission, where targeted mosquito control activities might be most beneficial to protect the communities.
The mosquito surveillance also showed that there are three dominant species in the region that accounted for 75% of all mosquitoes: Aedes notoscriptus (37%), Culex molestus (27%) and Culex australicus (11%). However, only Ae. notoscriptus was positive for M. ulcerans, indicating that mosquito control activities need to focus on this species (see Fig. 1)
Pilot trial (February-April 2021) – background
Last summer, the Beating Buruli project team designed a series of non-toxic mosquito reduction interventions to attempt to specifically and sustainably reduce local populations of Aedes (Ae.) notoscriptus, the container-breeding mosquito that is implicated in the transmission of Buruli ulcer (BU). The interventions did not include insecticide spraying, in response to community preferences raised in 2019. The aim of this pilot trial was to assess the effectiveness of this new approach in reducing mosquito numbers on the Mornington Peninsula.
Pilot trial – study design
- Ten zones containing a total of approximately 700 households in Rye and Blairgowrie were included in the pilot study during summer (February – April) 2021.
- Half the zones were randomly allocated as intervention zones, and the other half were control zones in which no interventions took place.
- In the intervention zones, mosquito reduction activities included the use of non-toxic sticky mosquito traps (Gravitraps), mosquito insect growth regulators, and community education and engagement to help residents identify, empty and/or remove water-filled containers on their properties that act as breeding habitats for container-breeding mosquitoes such as notoscriptus.
- Mosquito population numbers were monitored via Ovitraps before, during and after the intervention period.
During the intervention period, our Gravitraps had caught approximately 3,100 mosquitoes, and during the monitoring phases (before and after the intervention period) our Ovitraps had collected over 250,000 mosquito eggs (see Figure 1).
The mosquito data provided a lot of important and useful information about mosquito population dynamics, Mycobacterium (M.) ulcerans transmission and mosquito dispersal patterns. However, the data did not show a reduction in mosquito numbers in the intervention zones compared to the control zones after the trial.
This result is almost certainly partly due to the low community uptake of the intervention activities: only one quarter of households in the intervention areas participated. Based on similar studies that demonstrated a reduction in Aedes mosquito populations, we hoped that at least 80% of the households in the intervention areas would participate. However, there were many unoccupied households in the intervention areas that our study team did not receive permission to access. Some of these properties were observed from the street to contain multiple sources of standing water that could act as mosquito breeding habitats, and these 'hotspot' houses might have produced enough mosquitoes to affect the trial results.
The project team have re-assessed the study design based on the findings of the pilot trial, and have developed a modified and more localised (‘single-property-scale’) mosquito intervention to trial this summer (February–April 2022).
Fig 2: An Ae. notoscriptus mosquito caught on a sticky Gravitrap (A) and a close up of mosquito eggs on a piece of red felt taken from a monitoring trap (Ovitrap) (B).
Next steps for 2022
- Mosquito control intervention for summer 2022: Based on the results of the pilot trial last summer, the study team now plans to perform a single property-scale, citizen science-based mosquito reduction intervention on the Mornington Peninsula during summer 2022. This will determine whether the modified intervention can significantly reduce mosquito species known to carry ulcerans (the bacteria that cause BU) within a BU-endemic area. It is anticipated that approximately 60 households will be recruited and asked to select one of three intervention options, some of which they may already be conducting, and the effectiveness of each option will be monitored during the study. Recruitment for this intervention will start in early 2022.
- Further lab work: The mosquitoes that were collected during the pilot trial are still being processed to determine how many of them were carrying ulcerans. This information will also allow us to identify areas where mosquitoes carrying M. ulcerans are actively circulating so that future BU interventions could be focused on these potentially higher-risk areas.
- Possum faecal (scat) surveys are also underway across urban areas of Melbourne, Greater Geelong and the Mornington and Bellarine Peninsulas. Field staff will be collecting possum faecal pellets from publicly accessible sites that will then undergo ulcerans screening in the lab to identify those areas in which the bacteria are being actively shed into the environment by infected possums.
- Possum surveillance studies are also being planned for 2022 and 2023. These will involve monitoring free-ranging possums in areas of coastal Victoria where BU is known to occur. Revisiting the areas at regular intervals should allow long-term monitoring of the progression of BU disease in possums and its impact on animal welfare.
The Beating Buruli team would like to express our thanks for the community support we have received during our intervention activities to date. We look forward to continuing to work with communities on the Mornington Peninsula and other endemic areas, and we remain hopeful that together we will be able to stop the spread of Buruli ulcer in Victoria and more widely.
What is Buruli ulcer?
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 requires prolonged antibiotic treatment and sometimes surgery to remove damaged tissue and/or to promote healing. Buruli ulcer can however leave patients with significant cosmetic and sometimes functional damage to limbs, particularly if it there are delays in instituting therapy.
Buruli ulcer has been reported in 33 countries around the world including rural West Africa, Central Africa, New Guinea, Latin America and tropical regions of Asia.
Buruli ulcer in Victoria – past and present
In Australia, Buruli ulcer most commonly occurs in localised coastal areas of Victoria. The disease emerged dramatically on the Mornington Peninsula in the mid-2000s, beginning with a handful of cases near Sorrento and increasing to between 200-340 cases per year since 2017.
The Mornington and Bellarine peninsulas are associated with the highest number of cases in Victoria (see Fig. 3), however Frankston, Seaford, the South Eastern Bayside suburbs and East Gippsland are also considered to be endemic areas for Buruli ulcer transmission. (See ‘Who is at risk?’ below for more detail about risk areas in Victoria)
Fig. 4: Rates of Buruli ulcer cases in Victoria by local government area, from 1991 to 2020.
Since 2019, there has been Buruli ulcer cases who have reported no travel to known endemic areas identified in the Geelong suburb of Belmont, in Aireys Inlet and the Surf Coast. This suggests that local transmission of Buruli ulcer may be spreading into new areas.
In February 2021, local transmission of Buruli ulcer was reported in the inner Melbourne suburbs of Essendon, Moonee Ponds and Brunswick West, after genetic analysis of M. ulcerans bacteria isolated from human and possum cases of Buruli ulcers suggested a common source of infection in the area. This is the first non-coastal area in Victoria to be recognised as a potential area of transmission risk. In April 2022, this was extended to include the neighbouring suburbs of Pascoe Vale South and Strathmore.
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
Victoria's Department of Health (DH) has supported research into how Buruli ulcer is transmitted for more than a decade, including providing funding to refine development of an internationally recognized molecular test that has enabled detection of Buruli ulcer in the environment and earlier diagnosis and treatment. Recognising the infection early is important to minimise complications from this infection.
The ‘Beating Buruli in Victoria’ project received its first National Health and Medical Research grant in 2018, allowing the collaborative partnership established between the Victorian Department of Health, the Doherty Institute, University of Melbourne, Barwon Health, Austin Health, CSIRO, Agriculture Victoria, and the Mornington Peninsula Shire Council, to undertake ambitious and innovative research to better understand how Buruli ulcer is transmitted in Victoria, and to determine effective ways to reduce and prevent human infections.
Additional federal government funding was secured in 2020 to continue the research into this puzzling disease, through a series of epidemiological, field- and laboratory-based studies planned to take place on the Mornington and Bellarine peninsulas between 2021 and 2023. The ‘Beating Buruli in Victoria’ project hopes to actively disrupt disease transmission for the first time and lead to the development of evidence-based policies and guidelines that can help stop the spread of Buruli ulcer around Victoria and even globally.
Previously completed studies under the ‘Beating Buruli in Victoria’ project
Beating Buruli: the case-control study (2018-2020)
The Beating Buruli case control study was the first research component of the overall ‘Beating Buruli in Victoria’ project that investigated a range of risk and protective factors associated with Buruli ulcer.
It used a case control study design which involved asking people with Buruli ulcer (‘cases’) and people without it ('controls') to complete a short questionnaire. Field surveys were also conducted at the properties of study participants where a range of environmental samples were collected and then tested for Mycobacterium ulcerans at the laboratory.
Comparing questionnaire responses and field survey results from both cases and controls, the team were able to identify factors that increase a person's risk for getting Buruli ulcer and factors that can protect against getting the disease.
The study ran for a total of two years from September 2018 to September 2020. Results of this study are currently being prepared for publication.
Who conducted the study?
The study was jointly conducted by Barwon Health and the CSIRO with additional support being provided by the Department of Health and Human Services, Mornington Peninsula Shire Council, Deakin University, University of Melbourne and Agriculture Victoria.
Beating Buruli: the mosquito control study (2018-2020)
Findings from an earlier case-control study conducted in 2004 on the Bellarine Peninsula showed that getting bitten by mosquitoes, as well as gardening, were possible risk factors for getting Buruli ulcer, while wearing insect repellent protected against infection. Further research, including laboratory studies and mapping the distribution of Buruli ulcer lesions in human cases, strengthened the evidence that mosquitoes might play a significant role in transmission.
These findings were the basis for the planned second major research focus of this project, the Beating Buruli mosquito control study which planned to investigate the effect of mosquito control on the transmission of Buruli ulcer. In the planned research study, some areas were to receive an intensive mosquito control program including residual spraying using pyrethroid insecticides. However, the local government and some residents expressed a preference for interventions that did not involve spraying using pyrethroid insecticides, due to concerns around perceived health effects and possible collateral damage to other insect populations (particularly bees).
A decision was made to defer the intervention study to allow development of an alternative study proposal that did not involve residual spraying using pyrethroid insecticides.
Commonly asked questions about Buruli ulcer
What are the symptoms of Buruli ulcer?
Buruli ulcer usually progresses slowly over several weeks. Occasionally it can develop more rapidly. An ulcer may not be initially present. It can occur anywhere on the body but it is most common on exposed areas of the limbs, such as ankles, back of calf, around the knee, or forearms or around the elbow.
- Initially, a spot that looks like a mosquito or spider bite forms on the skin. This can be itchy and is usually painless, however some patients do notice pain. Small skin spots and bites are common but a feature of Buruli ulcer is that it doesn't settle with short courses of standard antibiotics and worsens instead of healing naturally.
- The spot usually gets bigger over days or weeks and may form a crusty, non-healing scab.
- Over time, the nodule (lump) scab turns into a or scab nodule (lump) then breaks down to reveal an ulcer, surrounded by a ring of red swelling, that continues to increase in size and is surrounded by a ring of red swelling.
- Sometimes an ulcer does not form, with the infection presenting as persistent localised pain and swelling (cellulitis), thickened or raised flat areas of red skin with pain and fever.
How long does it take for the symptoms of Buruli ulcer to appear?
It is estimated that in Victoria, the average time from exposure to the bacteria to the onset of first symptoms is about four and half months but can range from two to nine months. Cases are diagnosed year-round, however there is usually a peak in diagnoses in Victoria between June and November each year.
How is Buruli ulcer transmitted?
Buruli ulcer is an infection acquired from the environment. It is not yet known exactly how humans become infected with the bacteria, or where in the environment the bacteria prefer to live. The bacteria may enter through broken skin, and both mosquitoes and some water-dwelling insects have been implicated in the transmission pathway (see Fig. 4). Most cases report some form of skin trauma, including insect bites, prior to the development of the lesion. It is not spread person-to-person. The highest risk for infection is during the warmer months, but transmission can occur at any time of the year.
Fig. 5: Life cycle of the Aedes notoscriptus mosquito. In urban areas, Ae. notoscriptus breeds in standing water in containers such as pot plant saucers, bird baths, dog bowls and old tyres, and plants that hold water. The adults readily attack humans throughout the day in shaded areas but also feed during early mornings, evenings and nights. These mosquitoes are present throughout all of Australia, and can spread Murray Valley encephalitis, Ross River and Barmah Forest viruses and dog heartworm, and new data suggest they may also spread Mycobacterium ulcerans, the bacterium responsible for causing Buruli ulcer.
What is the treatment for Buruli ulcer?
Buruli ulcer can be treated with a course of special oral antibiotics. Surgery is sometimes used in combination with antibiotic therapy. Regular dressings are usually required. Complete healing usually takes between three and six months depending on the size of the ulcer.
As ulcers get bigger over time, early diagnosis and early commencement of effective treatment are important to minimise tissue loss and reduce the time until the ulcer heals.
Who is at risk?
People of any age can get infected. People who live in or visit the affected areas of Victoria (see Fig. 5) are considered at greatest risk.
- The highest risk is associated with the active transmission areas of Rye, Sorrento, Blairgowrie and Tootgarook on the Mornington Peninsula.
- There is a medium risk associated with areas in the Bellarine Peninsula (Ocean Grove, Barwon Heads, Point Lonsdale, Queenscliff), Frankston and Seaford areas.
- There is a low but material risk associated with the rest of the Bellarine and Mornington Peninsula, the South Eastern Bayside suburbs and East Gippsland.
Together, these are considered the endemic areas of Victoria for Buruli ulcer transmission. Buruli ulcer is rare outside these areas. Recent cases from Aireys Inlet, the Surf Coast and the Geelong suburb of Belmont, as well as Essendon, Moonee Ponds, Brunswick West, Pascoe Vale South and Strathmore in inner Melbourne, suggest that these may be emerging areas of local transmission, however the risk of transmission in these areas is currently considered low.
Fig. 6: Map of Victoria showing high-, medium- and low-risk areas for transmission of Buruli ulcer.
Evidence to date suggests that mosquitoes play a role in the transmission of M. ulcerans. Exposures to contaminated soil or water following outdoor activities have also been identified as possible sources for transmission. Therefore, the best way to prevent infection is through the use of simple precautionary measures.
Suggestions to reduce the risk of infection include:
- Wear gardening gloves, long-sleeved shirts and trousers when gardening or working outdoors.
- Avoid insect bites by using suitable insect repellents and long clothing, especially during the warmer months.
- Protect cuts or abrasions with sticking plasters.
- Promptly wash and cover any scratches or cuts you receive while working outdoors.
See your doctor if you have a skin lesion and mention the possibility of Buruli ulcer.
Advice for health professionals
Early diagnosis is critical to prevent skin and tissue loss - consider the diagnosis in patients with a persistent ulcer, nodule, papule, or oedema and cellulitis, especially on exposed parts of the body.
Follow the guidance in the Chief Health Officer Advisory on diagnosis and testing, making sure to take a dedicated swab or fresh tissue sample reserved for polymerase chain reaction (PCR) testing for the infection.
People of any age can get infected, and symptoms can occur four weeks to nine months after exposure to any endemic area; however, there are very different levels of risk associated with the parts of Victoria that are endemic.
Buruli ulcer is a routine notifiable condition and must be notified to the Department within five days of diagnosis.
Referral for treatment to doctors experienced in the management of this condition is recommended. The current mainstay of treatment is rifampicin-containing combination oral antibiotic therapy. Surgery may be used in combination with antibiotic therapy where indicated.
Reviewed 04 May 2022