Are mosquitoes to blame for the increase in Buruli ulcer outbreaks?
A disturbing increase in reported cases of the ‘Bairnsdale ulcer’ caused by a ‘flesh-eating’ bacteria in Victoria’s Mornington Peninsula has authorities on high alert, with the cause of the spread still a mystery.
The ulcer is caused by Mycobacterium ulcerans, a tropical bacterium. When it gets into the body, the toxins made by the bacteria destroy skin cells, small blood vessels and the fat under the skin, which leads to ulceration and skin loss.
Named the ‘Buruli ulcer’ overseas, it is largely confined to tropical and sub-tropical countries, particularly in west and central Africa, including Benin, Cameroon and Ghana. However, it is present in Australia and is on the increase in Victoria.
First noted in Victoria in the 1930s, the number of reported cases has been on the increase since 2013. Although apparently confined to coastal areas, the number of areas where cases have been reported is also on the increase.
According to an article in The Conversation, by Allen Cheng, Professor in Infectious Diseases at Monash University, the reasons for where and in whom infection occurs isn’t clear. “Circumstantial evidence seems to implicate mosquitoes, as the bacteria can be found in mosquitoes, occurs on exposed parts of the body where mosquitoes tend to bite, and seems to be associated with outdoor activities. So, covering up and using mosquito repellents would seem to be the best preventative measures,” Mr Cheng wrote.
“Oddly, cases seem to occur in very specific areas; on the Bellarine Peninsula, some towns seem to be ‘hotspots’ whereas others are spared. An intriguing lead that may partly explain this is the discovery that possums, and more specifically possum faeces, appeared to be infected, and sometimes without the possum apparently being unwell. Positive ‘possum poo’ seems to occur where human cases occur.”
According to Mr Cheng, this suggests the infection may be a zoonotic infection. “This is where human cases occur as a ‘spill over’ from what is otherwise an animal infection,” Mr Cheng wrote. “Clearly this isn’t the whole story, as Mycobacterium ulcerans infections occur in regions of the world with different mosquito and animal species.”
Investigations into how the Buruli ulcer is spread are ongoing, however because it is believed mosquitoes may play a role, the Victorian Government Department of Health and Human Services and other agencies have begun a mosquito surveillance program to help better understand the possible role of mosquitoes in the spread of the infection.
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Reworked extract from: Conversation.com, ‘Explainer: What Is The Flesh- Eating Bacterium That Causes Buruli Ulcer And How Can I Avoid It?’, September 21, 2017.