The ulcers are caused by a bacteria, Mycobacterium ulcerans, getting into the skin.
As the bacteria grows, it releases toxins which rot the skin, ultimately leading to an ulcer.
If untreated, the infection can eat away at the bone.
Victims develop huge, fluid-filled blisters containing dead flesh, with major surgery often required to cut them out.
Health authorities are urgently trying to work out what this tropical bacteria, typically found in Africa and South America, is doing in Victoria.
Nor do we know how it spreads. One theory is the bacteria is harboured by infected possums, and then spread from possums to humans via mosquitoes.
To avoid infection, the health department advises people to reduce the likelihood of insect bites by using repellent and wearing long-sleeved clothing and long trousers.
You should also cover cuts and scratches with sticking plaster so the bacterium cannot enter the skin. See a doctor if you have a persistent skin lesion.
A taskforce with researchers from the department, the CSIRO, the Doherty Institute and other leading research bodies is working to crack the problem, before the outbreak spreads further.
“Working with our partners, the project will identify interventions that we hope will actively disrupt disease transmission for the first time,” Victoria’s acting chief health officer, Dr Brett Sutton, said in a statement.
This will lead to the development of evidence-based policies and practices that can help stop the spread of the disease.
Over the past few weeks the taskforce has been collecting soil samples around the Mornington Peninsula, as well as collecting mosquitoes and faecal samples from possums.
Liam is The Age and Sydney Morning Herald’s science reporter