Doctors in Australia have called for urgent research into why a flesh-eating ulcer has become a "worsening epidemic" in the state of Victoria.
Local cases of Buruli ulcer, a skin disease most commonly found in Africa, have surged by 400% in the last four years, experts say.
Infections have also become more severe and spread to new areas.
Doctors do not know how to prevent the disease, which is caused by bacteria that breaks down tissue.
A record 275 new infections were recorded the state last year, marking a 51% increase on 2016.
Infectious diseases expert Dr Daniel O'Brien said cases of the Buruli ulcer, or Mycobacterium ulcerans disease, had become "frighteningly more common and also more severe" in the region.
It was unclear why the ulcer, typically found in tropical areas, had emerged in the temperate climate of Victoria, he said.
Writing in the Medical Journal of Australia, doctors have called for government funding to research the disease and its causes.
"No one understands what's happening and what's driving this epidemic," Dr O'Brien, a co-author, told the BBC.
"We can offer clues but not definitive advice. It's a mystery."
He said some theories involved factors such as rainfall, soil type and wildlife. Last year, authorities found traces of the bacteria in local possum faeces.
"The problem is, we don't have the time to sit around and pontificate about it - the epidemic has reached frightening proportions," he said.
The ulcers are difficult to treat and patients often experience a recovery period of between six and 12 months. Many people also have to undergo reconstructive surgery, Dr O'Brien added.
Victorian health authorities say they have spent more than A$1m (£550,000; $780,000) on researching the disease, and have started education campaigns to raise awareness about it.
Until a few years ago, infections were more commonly reported from tropical regions in Queensland with occasional cases in other states.
The disease is more commonly found in rural West Africa, Central Africa, New Guinea, Latin America and tropical regions of Asia.
In the developing world, the disease is associated with wetlands and stagnant water, however in Australia cases have largely been reported from coastal regions.
