Scientists in Australia have voiced concern about an apparent outbreak of Buruli ulcer, a flesh-eating disease that usually occurs in West and central Africa.
The infectious disease has seen a spike in cases in recent years in several parts of Australia but particularly in the state of Victoria.
In a study published Monday in the Medical Journal of Australia, the authors caution that the outbreak of the ulcers, described as an "epidemic" in the study, requires an "urgent scientific response." They report that Victoria is facing a worsening epidemic "defined by cases rapidly increasing in number, becoming more severe in nature, and occurring in new geographic areas."
In 2016, there were 182 new cases reported, a spike of 72%. But even this number was dwarfed by a further increase of 51% from November 2016 to the same month a year later. In November 2016 there were 156, which rose to 236 cases.
The environmental reservoir of the disease and how it spreads between humans is unknown. Most cases in Africa are associated with living near marshes and other aquatic environments. But in Australia cases are often linked to specific modes of transmission such as mosquitoes and possums, according to Andres Garchitorena, researcher at the Institute of Research and Development in France and an expert on Buruli ulcers, who was not involved in the most recent report.
"In Australia, it seems more to be a terrestrial transmission whereas in Africa, for example, the strain is very different and is mostly transmitted through aquatic ecosystems," Garchitorena said.
Doctors also do not know why cases are becoming more severe.
"One possibility is maybe there's some resistance to the antibiotics that they are using," Garchitorena said.
"It is difficult to prevent a disease when it is not known how infection is acquired," lead author and associate professor Daniel O'Brien, an infectious diseases consultant, wrote.
"The risk of infection appears to be seasonal, with an increased risk in the warmer months."
The study points to an alarming increase in new cases of the condition, also known locally as Bairnsdale ulcer, or Daintree ulcer.
The presence of the disease in the state has been known for decades -- the first case recorded was in 1948 -- but the spike in cases in recent years is of concern.
Australia has seen an increasing number of cases being reported since 2013, according to WHO.
Buruli ulcer is caused by the bacteria Mycobacterium ulcerans and results in severe destructive lesions of skin and soft tissue, the paper states. The bacterium is part of the same family of organisms that cause leprosy and tuberculosis, according to the World Health Organization.
"The way it creates the ulcers is that when it's inside your skin, it multiplies and it produces a toxin," Garchitorena said. "It mostly affects the fatty tissue. It starts generally with a small nodule, but over time it opens up and creates an ulcer."
Though some deaths from the disease have been reported, most cases are not life-threatening, according to Garchitorena.
"There are cases where people have died, but the most common outcome when it's not treated is handicap -- people may need an amputation or surgery with functional limitations for life," he said.
In 2017, 2206 cases were reported globally, compared to 1920 cases in 2016, with Australia and Nigeria reporting the most cases.
As the mode of transmission is unknown there are no prevention strategies against the disease.
The infection is treatable and cure rates are "approaching 100%" with antibiotics such as rifampicin and clarithromycin, but if not treated quickly, the disease can result in long-term disability and cosmetic deformity. Current antibiotic treatments only prevent surgery in 40% of patients, said Dr. Zlatko Kopecki, vice-president of the Australasian Wound & Tissue Repair Society. "Novel antibiotics or targeted antitoxin treatments are required as wound infection is a serious problem for thousands of patients with chronic wounds," he said last year.
The disease first appears as a painless bump or swelling and turns into a larger ulcer with "undermined borders" within four weeks. In some cases it can also affect bone, causing "gross deformities," according to WHO.
The demographic affects varies considerable across affected regions, with an estimated 48% of those affected in Africa under the age of 15, while just 10% affected are under that age in Australia.
"In Australia, it tends to infect people over 50 but younger people can be affected too. Most cases are diagnosed in the winter months but infection may have actually occurred in summer," said Sanjaya Senanayake, associate professor of medicine at The Australian National University last year when commenting on the recent rise in cases. "The route of infection is not certain but possibilities include fresh water, possum poo and insect bites."
The cause of the spike in Australia remains a mystery, the researchers state, particularly in the state of Victoria, home to one of the country's biggest cities, Melbourne.
Explanations of its spread in humans include theories that "(insect) bites, environmental contamination or trauma" may play a role, and both mosquitoes and possums are posited as carriers.
"Lesions most commonly occur on exposed body areas, suggesting that bites, environmental contamination or trauma may play a role in infection, and that clothing may protect against disease," the authors write, adding that "recent evidence indicates that human-to-human transmission does not occur, although cases are commonly clustered among families."
However, the study notes that the risk of infection "appears to be seasonal, with an increased risk in the warmer months."
Because many patients may require plastic surgery to repair damage from the lesions, the disease can be costly to treat. Average costs in Australia are $14,000 AUD ($11,000 US) per patient and the paper states an estimated cost to the state of Victoria in 2016 of more than $2.5 million ($2 million US).