Targeting mosquitoes reduces Buruli ulcer risk in Melbourne trial

A study published in Nature Microbiology and led by researchers in the Dept of Microbiology & Immunology (DMI), has found that mosquito control in an urban setting can reduce a person's risk of contracting Buruli ulcer by over 80 per cent.

This is the first evidence that suppressing mosquito populations directly protects people from the disease. Buruli ulcer is a serious infection caused by Mycobacterium ulcerans, a bacterium that can destroy skin and soft tissue if not treated early. Cases have increased in Victoria in recent years, with infections now occurring across coastal parts of Victoria and in many suburbs of Melbourne.

Building on previous research that identified a common Australian backyard mosquito as a critical part of the Buruli ulcer transmission cycle in Victoria, researchers from the Department of Microbiology & Immunology at the Peter Doherty Institute for Infection and Immunity (Doherty Institute) investigated whether targeted mosquito control could stop
people getting this infection.

The team conducted a randomised controlled trial across 12 areas in Melbourne’s inner north-west, including Brunswick West, Essendon and Moonee Ponds. Six areas received specialised mosquito control traps, known as autodissemination stations, to see if they could reduce mosquito numbers and, in turn, whether fewer mosquitoes led to fewer Buruli ulcer infections in people living in those areas, compared with the areas without traps.

After eight weeks they found that mosquito egg counts had dropped by around 70 per cent across areas with the control stations.

The researchers then examined whether this reduction in mosquito populations translated to fewer human infections, a complex task given it takes weeks to months for Buruli ulcer to develop in the skin after being bitten.

Dr Andrew Buultjens, Senior Research Fellow in the Stinear Research Group (DMI), and co-first author of the study, said that the team could not simply compare diagnosis dates to assess when or where infections were acquired.

“Because symptoms typically appear around five months after infection, we had to work backwards to estimate when infection happened and use forensic genomic analysis to determine which cases were acquired locally,” Dr Buultjens said.

By intersecting timing and location of infections, we found that when we reduced mosquito numbers by 70 per cent over an eight-week period, there was an 83 per cent lower incidence of Buruli ulcer among people living nearby.

Professor Tim Stinear, Redmond Barry Distinguished Professor and Head of the Stinear Research Group (DMI) said the findings have for the first time unlocked a feasible way to prevent Buruli ulcer across an urban area, thus controlling this critical infection.

“While we knew mosquitoes played an important role in spreading Mycobacterium ulcerans, this study shows for the first time that reducing mosquito populations can reduce the risk of disease in people,” Professor Stinear said.

These findings provide evidence for public health control strategies to help communities affected by Buruli ulcer.

This article was originally published by the Doherty Institute on 1st September.