A severe tissue-destroying ulcer once rare in Australia is rapidly spreading and is now at epidemic proportions in regions of Victoria, prompting infectious diseases experts to call for urgent research into how it is contracted and spread.

In an article published in the Medical Journal of Australia (MJA) on Monday, authors led by associate professor Daniel O’Brien from Barwon Health said incidents of Buruli ulcer were on the rise but researchers were baffled as to why Victoria was being particularly affected. There have been no reported cases in New South Wales, South Australia or Tasmania.

In 2016, there were 182 new cases of the ulcer in Victoria – the highest ever reported by 72%, O’Brien said. But he added that cases reported until 11 November 2017 had further increased by 51% compared with the same period in 2016, from 156 cases to 236 cases.

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“Despite being recognised in Victoria since 1948, efforts to control the disease have been severely hampered because the environmental reservoir and mode of transmission to humans remain unknown,” O’Brien said. “It is difficult to prevent a disease when it is not known how infection is acquired.”

The first sign of infection is usually a painless lump on the skin often dismissed as an insect bite. The slow-moving infection then burrows into a layer of fat located between the skin and the lining that covers muscles. It is in this fatty layer that the infection takes hold, spreading sideways and through the body, destroying tissue along the way, before eventually erupting back through the skin in the form of an ulcer. Those with the infection often have no idea the infection has taken hold until the ulcer appears. But when the ulcer does erupt, the pain can be extreme.

Anyone is susceptible. While the infection responds to a roughly eight-week course of antibiotics, in rare cases surgery to remove skin or even amputation is needed.

Prof Paul Johnson is an internationally renowned Buruli ulcer expert and has been studying the infection since 1993. He led the development of a highly accurate diagnostic test for the bacteria that causes the disease and is now based at Austin Health in Victoria, where he is trying to understand why the infection is most common on the Bellarine and Mornington peninsulas.

This has confused researchers because the disease is most often associated with swampland areas in tropical countries and it is found at the greatest frequency in Africa. Cases are also becoming more severe.

“It seems to occur in very specific areas of Victoria,” Johnson said. “If you don’t enter an endemic area, you don’t get the disease. But what is it about the area that contains it, and what happens to you that means you pick the disease up from that area? Those are the big questions we’ve been asking.”

He also said the infection had a “very odd” distribution. “When you enter an endemic area, it looks the same as the area you just left,” he said.

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Johnson believes it is most likely the bacteria that causes the ulcer, Mycobacterium ulcerans, is being spread by mosquitoes and possums. His research team caught a large number of mosquitoes in affected areas and found a small proportion did carry the bacteria.

They then found ringtail possums in affected areas excreted the bacteria in their faeces.

“Our hypothesis is really that this is a disease of possums,” he said. “It sweeps through possums and contaminates the local environment through their poo including contaminating mosquitoes, and people are picking it up predominately from biting insects, and maybe directly from possums.”

There could be other modes of transmission though, he said, and he said researchers did not know how possums contracted and spread the disease. Johnson said that unlike malaria, which is rapidly spread by mosquitoes, transmission of Mycobacterium ulcerans appeared to be more inefficient.

The authors of the MJA article called for urgent government funding to research the bacteria and to carry out an exhaustive examination of the environments it is found, including looking at local animals and any interaction with people.

“The time to act is now,” the authors wrote.

Johnson agreed but added there were some precautions people in affected areas could take such as avoiding mosquito bites, cleaning and covering any cuts sustained outdoors, and going to the doctor if they had any concerns.