The spread of a severe tissue-destroying ulcer once rare in Australia to a new geographic area in Queensland has infectious disease experts worried.

The Buruli ulcer, also known as the Bairnsdale ulcer or Daintree ulcer, is an infection that eventually leads to an eruption of painful skin ulcers that fail to heal. There have been no reported cases in New South Wales, South Australia or Tasmania, with the disease so far confined to the Douglas Shire in far north Queensland between Mossman and just beyond the Daintree River, and to Victoria’s Bellarine and Mornington peninsulas.

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But doctors are concerned because, in the past two years, three cases of the usually geographically confined disease have emerged in the Atherton Tablelands, south of its usual catchment area in far-north Queensland. While the disease is much rarer in Queensland than Victoria, with an average of two cases per year, there are occasional spikes, such as in 2011 when 60 cases were recorded. Victoria saw a record 340 cases of the disease in 2018 and is approaching a similar number for 2019. Internationally renowned Buruli ulcer expert Prof Paul Johnson said that despite the comparatively low number of Queensland cases, the movement of the disease outside of its normal range was a concern.

“We are used to the ulcer moving in Victoria, and what is interesting is it hasn’t moved much up there in Queensland over the years,” Johnson, of the University of Melbourne, said. “Now the cases diagnosed in the Tablelands are not a dramatic change of area, that’s still quite close to the Douglas Shire, but any move is worth reporting to alert doctors to keep an eye out. The disease is really quite treatable if it is caught early. But doctors can’t treat it if they fail to identify it because they’ve never seen it.”

The disease is usually associated with swampland areas in tropical countries and is most common in Africa. 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 and can lead to amputations.

Efforts to eradicate the disease have been difficult because researchers have been baffled by how it is contracted and spread. Johnson believes it is most likely the bacteria that causes the ulcer, Mycobacterium ulcerans, is being spread in Victoria by mosquitoes and possums. In Victoria, 40% of cases are found in visitors to the Mornington and Bellarine peninsulas. The incubation period is about five months, so people often visit the beachside areas in the summer months but only present with the disease in the colder months after returning to their home areas, where doctors may not be familiar with the disease and therefore may not immediately diagnose it.

“One of the peak times for transmission in Victoria is approaching, which is summer,” Johnson said. “People are planning their summer holidays to the peninsulas and I would urge those people to protect themselves against insect bites.” One decade ago, Victoria saw about 35 cases of the ulcer each year but now sees hundreds of cases. Transmission is also high in autumn.

Prof Tim Stinear, the scientific director of the Doherty Applied Microbial Genomics Centre, said it was concerning the disease had moved from low-lying areas of Queensland and into the hilly tablelands.

“In Victoria we saw it jump from the east of the state to the Bellarine peninsula so movement does happen,” he said. “Even larger jumps have been documented overseas. So I think any shift is significant.”