In the last year, cases of a ghastly but mysterious flesh-eating bacterial infection have more than doubled in Victoria, Australia, raising alarm among health experts.

There were 239 cases of the flesh-eating infections in the past 12 months, according to figures (PDF) released this week by health authorities. In 2016, there were only 102 reported cases, while 2015 and 2014 tallied just 58 and 47. And the rate of new infections is currently skyrocketing: in the past few months, case counts hit nine per week, according to Australia’s Nine News. The number of severe cases has also doubled.

While the rises alone are enough to worry health experts, the fact that virtually nothing is known about the cause of the infection has some dismayed.

“I’m at the forefront as a clinician trying to treat patients and getting more and more overwhelmed but also distressed at the fact that we are doing nothing to try and prevent people getting it in the first place,” Dr. Daniel O’Brien, of Royal Melbourne and Geelong hospitals, told Nine News.

Baffling bacteria

The infections are caused by Mycobacterium ulcerans, a slow-growing bacterium that causes gaping, palm-sized ulcers. Sometimes called Buruli ulcers, the lesions seem to dissolve skin and gnaw away at tissue. The bacteria are known to lurk around Victoria, but experts don’t know where it lives or how it spreads.

“There are theories about transmission via mosquitos, theories about it being in the soil and getting through wounds, theories about whether some animals are involved, in that we know that some possums can be affected by it,” O’Brien said. “But we don’t actually know where it lives, why it’s there, and how it gets spread to humans. How can we possibility halt an epidemic when we don’t have that basic information?”

The bacterium was first identified in Australia in 1948, but the ulcers get their name from Buruli county (now called Nakasongola) in Uganda, where researchers reported large numbers of ulcers in the 1960s.

It’s now known to skulk in at least 33 countries, and the World Health Organization considers it “largely a problem of the poor in remote rural areas (PDF).” It causes a few thousand cases worldwide each year, most of which are in children under the age of 15.

Antibiotics are usually effective at treating the lesions. But, early treatment is critical to reducing skin loss and tissue damage. Victims often need surgery to clean out dead flesh and repair wounds.

Zombie limbs

There are currently no prevention strategies or vaccines. Despite decades of knowing about the bacteria, researchers are still stumped by them. A study published just this April added weight to the idea that the bacteria are somehow linked to disturbed water sources, such as those with flooding or deforestation.

A study out last month looked at where the ulcers show up on people. The study of 579 patients found that they tend to cluster on arms and legs. The researchers, co-led by O’Brien, concluded:

“We propose that targeting behavior by biting insects rather than direct contact with a contaminated environment best explains the lesion distribution we observed.”

One likely source of confusion for researchers is the slow-growing nature of M. ulcerans. It’s unclear how quickly symptoms show up after a person is infected, but authorities estimate that it’s somewhere in the range of four weeks to nine months. Such a large window can make it difficult to pinpoint when or where an exposure occurred, let alone how.

“For me this is an urgent health problem that our community needs addressed,” O’Brien said. “I think our government should be putting significant amounts of money into trying to stop it and that means research.”

This week, a 13-year-old girl from Tyabb, Victoria, started an online petition to urge Health Minister Greg Hunt to provide more research funding for the disease. The girl was stricken with a Buruli ulcer on her knee in April and is still recovering. She needed three surgeries to clear out rotting flesh. (Here's a picture of her ulcer, but warning, it's gruesome.)

“It’s still not looking that great,” she said. “We call it the zombie leg.”