How is Buruli ulcer transmitted?

The main transmission routes are mosquito bites and contact with Mycobacterium ulcerans in soil contaminated by possum droppings. Ulcers most commonly appear on the arms and legs, consistent with mosquito-exposed skin. The bacteria are carried by brushtail and ringtail possums in endemic areas. Human-to-human transmission is not a recognised feature of the disease.

What does Buruli ulcer look like at first?

It typically starts as a small, firm, painless lump under the skin — easily confused with an insect bite, a cyst, or a lipoma. Over weeks to months the overlying skin breaks down, turns black, and forms a slowly enlarging ulcer that can extend beyond the visible edge. The painlessness is a direct effect of mycolactone — a toxin produced by the bacterium — which destroys nerve endings and suppresses the local immune response.

Where in Australia is the risk highest?

Victoria — particularly the Mornington Peninsula, Bellarine Peninsula, Geelong, and parts of inner Melbourne — accounts for the majority of Australian cases. Risk areas also include the south NSW coast around Batemans Bay, the Daintree and other parts of coastal Queensland, and around Darwin. Cases presenting in other cities typically acquired infection during travel to these endemic areas months earlier.

Buruli ulcer: Victoria records 426 cases as summer season opens

Victoria hit a record 426 confirmed Buruli ulcer cases last year. Researchers who study the disease describe the state as, effectively, the global centre of a condition that few Australians have heard of.

Halloween is as good a date as any to know about it — because Buruli ulcer is acquired in summer and autumn, and the cases that will present to GPs over the next six months are being contracted right now.

What Buruli ulcer actually is

Buruli ulcer is caused by Mycobacterium ulcerans, a slow-growing bacterium that produces a toxin called mycolactone. Mycolactone destroys skin and subcutaneous tissue and suppresses the local immune response. The result is a lesion that expands silently, often for months, before becoming visible. The painlessness of Buruli ulcer — which most patients describe as strange — is a direct effect of mycolactone destroying nerve endings in the infected area. By the time the wound looks serious, it may have been expanding beneath the surface for a long time.

Transmission occurs primarily through mosquito bites and through contact with soil contaminated by possum droppings. Brushtail and ringtail possums carry the bacteria in endemic areas of Victoria, shedding it in their droppings, which can then enter human skin through minor cuts and abrasions. The mosquito pathway appears to be the dominant route: a 2026 study published in Nature Microbiology found that interventions reducing mosquito populations in endemic areas correlated with fewer human Buruli ulcer cases, strengthening the mosquito-as-primary-vector hypothesis.

Endemic areas and the scale of the problem

Victoria — particularly the Mornington Peninsula, Bellarine Peninsula, Geelong, and some inner Melbourne suburbs — accounts for the majority of Australian cases, with 426 confirmed last year. Cases also occur on the south NSW coast around Batemans Bay, in coastal Queensland (sometimes described as Daintree ulcer), and around Darwin.

The geographic specificity matters in two directions. The risk is tightly localised — but that localisation includes some of Australia’s most densely populated and visited coastal regions. And it means cases frequently present to GPs or dermatologists far outside the endemic zone. A patient who spent summer on the Mornington Peninsula and returns to Brisbane before developing symptoms five months later arrives at a Brisbane GP with a puzzling painless skin lesion, no active holiday illness to report, and no obvious geographic red flag on the day of presentation. That consultation pattern — delayed presentation away from the acquisition site — is one of the reasons Buruli ulcer is underdiagnosed in Australia.

Both-and: underdiagnosed and increasingly recognised

There is a genuine tension in how Buruli ulcer sits in the medical literature. On one hand it is underdiagnosed — the long incubation period, the nondescript early lesion appearance, and the geographic concentration all contribute to delayed or missed diagnoses. On the other hand, case counts in Victoria have risen for years, the clinical literature has expanded substantially, and GPs in endemic areas increasingly encounter it.

The question of what is driving rising case counts is not fully settled. A wetter environment that supports larger possum populations, urban expansion into possum habitat, and increased outdoor recreation in endemic coastal zones are all cited. Researchers have explored BCG vaccination of possum populations as an environmental intervention that could reduce the reservoir; early modelling is promising but this has not been implemented at scale. An edible possum vaccine is in development.

On treatment: the standard six-to-eight-week antibiotic course (rifampicin plus clarithromycin or moxifloxacin) is effective for early-stage lesions, though about 20 per cent of patients cannot complete it due to adverse effects. A current Australian trial registered with the ANZCTR is testing a 10-day course as a potentially better-tolerated alternative. Surgery is required when there is significant tissue damage or poor healing.

Earlier diagnosis is consistently associated with a shorter and less invasive treatment course. This is not a condition where watchful waiting is helpful.

2 cents: what to do with this this summer

Mosquito season has opened. The infections being acquired this month and through November and December will present to GPs in the first half of 2027. Three practical points.

Reduce mosquito exposure in endemic areas. Long sleeves and trousers during peak mosquito periods, DEET-containing insect repellent on exposed skin, removal of standing water from gardens, and mosquito traps. The Nature Microbiology data suggests mosquito reduction is the most actionable individual-level lever.

Cover wounds during outdoor work or gardening in endemic zones. Wash cuts and abrasions promptly with soap and water and apply antiseptic before any soil contact. The entry route for M. ulcerans from possum-contaminated soil is broken skin.

Know the lesion pattern. A firm, painless skin nodule that develops on an arm or leg — particularly in someone who has recently spent time in an endemic area — is worth a GP review. Painless is not a signal of minor significance here; it is a feature of how this bacterium behaves. A PCR swab from the lesion edge is the diagnostic standard. Earlier investigation leads to an easier treatment course.

Verdict: yes — worth knowing about.