Mosquitoes spread flesh-eating bacteria that causes Buruli ulcer from possums to humans, scientists say

• In short: Scientists say they've confirmed a long-suspected link between mosquitoes and the spread of the flesh-eating bacteria that causes the Buruli ulcer.
• The ulcer was first detected in Australia in the 1940s, and its diagnosis has grown significantly in Victoria in recent years.
• What's next? The team behind the research says their study will help provide people with guidance to protect themselves against the ulcer, but others in the field say there is more to be revealed about why the bacteria is spreading.

Researchers say they have confirmed a theory that a flesh-eating bacteria that affected hundreds of Australians last year is being spread from infected possums to humans by mosquito bites.

The bacteria Mycobacterium ulcerans (M. ulcerans) creates toxins that destroy skin cells, blood vessels and fat under the skin, causing the Buruli ulcer.

According to Victoria's health department, the Buruli ulcer often appears as a spot that "looks like a mosquito or spider bite", but grows bigger over days or weeks.

There is usually no fever or other signs of infection, but the ulcer will continue to grow.

Buruli ulcer has been reported in dozens of countries around the world, and was first diagnosed in Australia in the 1940s.

Researchers at Victoria's Doherty Institute this week published a paper in the journal Nature Microbiology they said answered a question that had "perplexed scientists" for decades.

"We're excited by this because it's the end of an 80-year mystery about how this disease is being spread," lead researcher Tim Stinear told RN Breakfast.

Paper the result of five-year study

The research team focused on Melbourne's Mornington Peninsula, where they caught and tested 65,000 mosquitoes between 2016 and 2021.

Through genome sequencing, the team established the genetic make-up of bacteria in two types of mosquitoes was identical to humans who contracted Buluri ulcers in the area.

The research team said they had "long suspected" the mosquito link, but that it was unusual for a bacterium like M. ulcerans to be spread by an insect bite.

"But we have the first real information that we can give people to protect themselves from this infection," Professor Stinear said.

Cases of the skin disease have risen dramatically in recent years.

Buruli ulcer infections are found in certain areas along the Mornington Peninsula, parts of Geelong as well as suburbs in inner Melbourne.

"Ten years ago, we were getting about 20 to 30 cases a year across Australia," Professor Stinear said.

"We had 363 confirmed just in Victoria last year.

"This is creeping through the suburbs of Melbourne and Geelong and into New South Wales."

Research 'a piece of the puzzle'

Associate professor of infectious diseases at Deakin University Eugene Athan, who was not involved in the study and has also researched Buluri ulcer, said the findings were "very interesting".

"It's a piece of the puzzle, but I don't think it's the whole story," Dr Athan said.

"The things we don't still fully understand is that separate to mosquitoes, why would people potentially still get exposed and develop infection?

"And why has the Buruli moved so dramatically in the last 70 years in Victoria … and now we're seeing it in peri-urban areas.

"It's sort of galloping along, and it certainly increased very significantly in the last three years."

He said there were environmental factors that were conducive to the M. ulcernus bacteria thriving, but it was not known what was introducing the bacteria to new environments for the first time.

"We think wildlife may be a factor," he said.

"Climate change may also be a factor, but we haven't conclusively connected the two yet."

Identifing and treating Buluri ulcer

The Doherty researchers said their research was significant because it would allow people to take preventative steps against the ulcer, such as using insect repellent and removing stagnant water from around homes.

"It often starts as a mosquito bite that doesn't look quite right, and then doesn't heal like it should," Professor Stinear said.

"From the time you get bitten by that mosquito to the time you see the the infection, it's about four to five months."

Dr Athan said covering up while gardening or working outdoors, and washing wounds and scratches immediately had also been shown to be protective measures against the Buruli ulcer.

The Buruli ulcer is usually diagnosed by a doctor, and generally requires a six-to-eight-week course of antibiotics, according to Victoria's health department. 

"If it is Buruli ulcer then there are very effective antibiotics that can be prescribed so it's treatable. Buruli ulcer doesn't kill you,"  Professor Stinear said.

Ways to reduce your risk of infection from Buruli ulcer

• Reduce mosquito breeding sites around houses and other accommodation by reducing areas where water can pool
• Mosquito-proof your home by securing insect screens on accommodation.
• Avoid mosquito bites by using personal insect repellent and covering up by wearing long, loose-fitting, light-coloured clothing
• Avoiding mosquito-prone areas 
• When gardening, working or spending time outdoors wear gardening gloves, long-sleeved shirts and trousers
• Protect cuts and abrasions with a dressing
• Promptly wash any new scratches or cuts you receive with soap
• Wash exposed skin contaminated by soil or water following outdoor activities

Source: Better Health