Buruli ulcer spreads into Melbourne suburbs as researchers test mosquito control to curb the flesh-eating infection

Victoria recorded 426 cases of Buruli ulcer in 2025 alone, more than any other Australian state, and the infection is no longer confined to the coast. Inner north-west Melbourne suburbs, including Essendon, Brunswick West and Moonee Ponds, are now part of a new cluster, with transmission reported in suburban backyards.

Buruli ulcer is a skin infection caused by the bacterium Mycobacterium ulcerans. It begins as a small, often painless inflammation after a mosquito bite, and it may go unnoticed for months. After many weeks it turns into a disfiguring ulcer. Left untreated, the ulcer keeps growing, with loss of skin and muscle.

Treatment is an eight-week course of antibiotics, but recovery is slower than for other common skin infections. Healing depends heavily on the state of the ulcer when treatment starts, and it can take more than four months.

The bacterium also infects urban wildlife such as possums, which develop symptoms similar to those in people. Recent research has shown that mosquitoes pass it to humans. The species most closely linked with at-risk areas is Aedes notoscriptus, the Australian backyard mosquito, which is widespread and breeds in water-holding containers in suburban areas. Other routes of infection may exist, but health authorities say preventing mosquito bites is the best protection.

Buruli ulcer has been reported in more than 30 countries, across Africa, South America and the Western Pacific. In Australia it has appeared in Victoria, Far North Queensland, the Northern Territory and New South Wales. Since it became notifiable in NSW, six cases have been reported on the south coast. There was concern that the Victorian outbreak had crossed the border, but genomic analysis suggests the NSW cases come from a separate outbreak. That raises open questions about how widespread the pathogen is and what conditions lead to human infection in new regions. The researchers say surveillance beyond known areas of activity is needed.

Repellents and reduced mosquito exposure have been standard advice for decades, but insecticides are unlikely to cut suburban mosquito numbers in the long term. Véronique Paris and Andrew Buultjens led a Victorian study testing another approach: autodissemination stations. Each offers a breeding site, lured by a smelly mix of water and yeast. Inside, a gauze strip is coated with pyriproxyfen, an insect growth regulator, and Beauveria bassiana, an insect-specific fungus. The fungus kills the mosquito after it leaves, but before then it carries the agents to other containers where it lays eggs.

After eight weeks, mosquito egg counts were 70% lower in treatment areas than in control areas. Measuring effects on disease is harder because symptoms appear almost five months after infection, so the team worked backwards to estimate infection timing and used genomic analysis to identify locally acquired cases. At the predicted peak of the effect, incidence was estimated to be 83 per cent lower in treatment areas. Greater mosquito reductions went with greater apparent protection.

There are caveats. The stations are not yet sold in Australia, though regulatory approval is described as imminent and similar products are being tested. The study used large numbers of stations, so the effect of one household using them is unclear.

With El Niño expected to bring an early start to summer heat, and hot, relatively dry conditions forecast for eastern Australia, backyard mosquitoes remain a concern because water persists around homes. The advice: refill bird baths weekly, clear gutters, cover water tanks, and empty and refill wildlife water at least weekly. Keep using repellent and wear long sleeves, long pants and enclosed shoes outdoors.