80-year Buruli ulcer mystery solved

Up until very recently, scientists have been confounded by how people contract Buruli ulcer, ever since the discovery of Mycobacterium ulcerans (M. ulcerans) in the 1940s in Australia. A recent alarming surge in cases in and around Melbourne and Geelong caused this hitherto neglected tropical skin disease to become an important public health issue in Victoria, creating a pressing need for further research into what was causing the spread.

Following a concerted effort, a team of researchers has now solved the 80-year mystery. Led by University of Melbourne’s Professor Tim Stinear, Director of the WHO Collaborating Centre for Mycobacterium ulcerans at the Peter Doherty Institute for Infection and Immunity (Doherty Institute), the group’s findings categorically confirm mosquitoes as the primary vectors transmitting the ulcer-causing bacteria M. ulcerans from the environment to people. Their results have been published in Nature Microbiology.

Focusing on the Mornington Peninsula, a seaside region outside of Melbourne with one of the highest incidences of Buruli ulcer in the world, the Beating Buruli in Victoria project team trapped and tested more than 65,000 mosquitoes between 2016 and 2021.

Led by the Doherty Institute at the University of Melbourne, the collaborative research team brought together partners from the Bio21 Institute, Agriculture Victoria, Austin Health, Victorian Department of Health, the Mornington Peninsular Shire, CSIRO and more.

“How Buruli ulcer is spread to people has baffled scientists and public health experts for decades,” Stinear said. “So now that mystery is solved, with our five-year study revealing that mosquitoes transmit M. ulcerans in south-eastern Australia, making mosquito bite prevention and mosquito control obvious forms of prevention.”

Advanced techniques were employed in the research, including the use of forensic-level genomics.

“Thanks to genome sequencing, we discovered that the genetic make-up of the bacteria M. ulcerans in mosquitoes was identical to that found in Buruli ulcer patients in the study area,” said Dr Peter Mee, Research Scientist at Agriculture Victoria and one of the lead authors of the paper.

“This was a key part of a compelling body of evidence pointing to mosquitoes as the transmission link.”

Professor Paul Johnson, infectious diseases physician at Austin Health, said it was initially challenging to convince others that mosquitoes might be spreading Buruli ulcer.

“We long suspected mosquitoes were involved, but there is no precedence for a bacterial infection like Buruli ulcer being transmitted this way. Our team faced considerable scepticism, so we gathered irrefutable evidence to support our claim,” Johnson said.

“This research is significant because we can all take simple actions, like applying insect repellent and removing stagnant water around the house, to protect the community and reduce the risk of Buruli ulcer.”

Over the last two decades, there has been an exponential increase in reported cases in Victoria, escalating from 12 in 2003 to 363 in 2023 — the highest count to date.

The Royal Melbourne Hospital’s Dr Katherine Gibney, an infectious diseases and public health physician and one of the study leads at the Doherty Institute, stressed the importance of ongoing wildlife and mosquito population monitoring — a ‘One Health’ approach.

“Maintaining this type of mosquito surveillance work could offer crucial insights into the epidemiology of Buruli ulcer in the region and inform public health interventions aimed at controlling the disease,” Gibney said.

The Beating Buruli in Victoria team is in the process of rolling out a new trial aimed at reducing mosquito populations in urban areas, specifically around Brunswick West, Pascoe Vale South, Moonee Ponds and Essendon in Victoria, using state-of-the-art, environmentally friendly mosquito traps.

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