Flesh-eating bacteria spread from possums and mozzies. But Buruli ulcers are preventable and treatable
- Written by Cameron Webb, Clinical Associate Professor, School of Medical Science & Sydney Infectious Diseases Institute; Principal Hospital Scientist, University of Sydney
A number of cases of the flesh-eating Buruli ulcer have now been detected on the New South Wales south coast.
There is growing evidence mosquitoes are at least partly responsible for the spread of this “flesh-eating” bacteria, with possums also implicated. Health authorities have urged locals to avoid mosquito bites.
Cases of Buruli ulcer are usually concentrated to parts of Victoria. So why is it being found in NSW? And how does a mozzie bite turn into a flesh-eating ulcer?
Here’s what we know about this bacteria, how it spreads, and how you can prevent and treat these ulcers.
It starts as a painless mozzie bite
The bacterium Mycobacterium ulcerans is responsible for a skin infection known as Buruli ulcer.
It can take a long time after infection before the symptoms show. Over many months, what may first look like a small, painless mosquito bite develops into a disfiguring ulcer that, if left untreated, can continue increasing in size.
Treatment is readily available. This usually involves a six to eight week course of specific antibiotics, sometimes supported with surgery to remove the infected tissue. However, delays can make it more difficult to treat.
Where does it come from?
Buruli ulcer has been reported in more than 30 countries including in Africa, South America and the Western Pacific.
In Australia, Buruli ulcer has been reported in several states, including Queensland, NSW and Northern Territory but most activity has been in Victoria.
In Australia, possums can play a role in the spread of Mycobacterium ulcerans. They act as “reservoirs” of the pathogen, from which it can spread to people.
Possums themselves can also suffer symptoms of infection, with ulcers similar to those in humans.
How it gets from possums to people
There are likely a number of different ways to get infected. But research shows mosquitoes may be a key culprit.
For many years, there has been evidence of Mycobacterium ulcerans in mosquitoes collected from trapping programs. This includes the types of mosquitoes that commonly bite people.
Most recently, the studies took the analysis further with genomic testing linking Mycobacterium ulcerans to possums, people and mosquitoes.
The mosquito of greatest concern is widespread in Australia and closely associated with suburban areas. Commonly known as the Australian backyard mosquito, Aedes notoscriptus is a nuisance-biting pest and has been implicated in the spread of pathogens such as Ross River virus.
Buruli ulcer cases have been reported in areas were both mosquitoes and possums carry Mycobacterium ulcerans.
Are cases on the rise?
Since the ulcers were first described in the Bairnsdale region of Victoria in the 1940s, there has been a rise in both the number of cases and where they’re found.
In 2006, the first case was reported in NSW. A small cluster of cases was then reported on the NSW South Coast in 2023.
Does this mean the bacteria is spreading north from Victoria? Perhaps not.
A detailed genomic analysis of the NSW cases demonstrated they were genetically distinct from those prevalent in Victoria. Rather than a gradual march north from Victoria, this suggests there has been activity in the region for many years.
If NSW follows Victoria’s pattern, we may see reports of cases start out slowly in specific regions, such as Batemans Bay, before increasing and then spreading to new areas.
Can authorities predict where cases will spread to next?
NSW Health manages an extensive network of mosquito monitoring locations across the state. This network allows authorities to track mosquito populations and track any activity of mosquito-borne pathogens.
But while this program is good at providing an early warning of viral pathogens such as the Ross River, Japanese encephalitis, or Murray Valley encephalitis viruses, testing mosquitoes hasn’t been shown to be as reliable in detecting Mycobacterium ulcerans.
Recent studies found there could be a delay of up to six years between the arrival of the pathogen and infection of people in new areas.
Rather than looking at testing mosquitoes, this study suggests surveys of possum poo may be a more effective way to survey for new activity of Mycobacterium ulcerans.
How can I protect myself and family?
Outbreaks of “flesh eating” bacteria sound dramatic, especially as there’s no vaccine. But don’t panic: the steps you take to prevent infection are the same you follow to stop nuisance-biting mosquitoes and other mosquito-borne diseases.
When outdoors, use insect repellent on exposed skin to stop mosquito bites and cover up with long-sleeved shirt, long pants and covered shoes.
It’s also important to stop mosquitoes buzzing about your backyard. Mosquitoes, especially Aedes notoscriptus, lay eggs wherever water collects after rainfall. This could be bird baths, drains, sump pits, potted plant saucers and a wide range of containers.
Clean out your gutters and drains so water flows easily out of them and throw away any containers collecting water. Make sure your rainwater tank is screened too.
Read more: It’s warming up and mozzies are coming. Here’s how to mosquito-proof your backyard
Authors: Cameron Webb, Clinical Associate Professor, School of Medical Science & Sydney Infectious Diseases Institute; Principal Hospital Scientist, University of Sydney
