Flesh-eating ulcer cases on rise across the ditch

Possums in Australia are spreading a hideous human disease called Buruli ulcer. The disease usually shows up as a tiny swelling on people’s legs and arms, growing to produce big edematous, pus-filled abscesses, devouring flesh to the bone and, in the worst cases, leading to excisions, skin grafts and amputated limbs. Youngsters are more at risk than older people.

Mycobacterium ulcerans – a bacterial cousin of human tuberculosis, bovine Tb, and leprosy – causes Buruli ulcer.

The disease is commonest in Africa but infects thousands of people every year in 30 other mainly tropical countries, including Indonesia and New Guinea. There is no effective vaccine against the disease but antibiotics are effective if it is diagnosed early enough.

Buruli ulcer was first identified in the outskirts of Melbourne in the 1930s and remained localised there until 2009, when it unexpectedly turned up in North Queensland. The Australian Medical Journal now reports a worsening epidemic with 17 cases in 2009 but 275 cases last year.

In its African homeland, the disease usually infects poor people living in remote areas, and is often associated with swamps and wetlands, flooding, new irrigation systems, and dam building. Throughout Africa and elsewhere, the ulcer bacterium has been found in small aquatic insects known as ‘‘creeping water bugs’’ and they may play a part as spreaders of the disease. But nobody knows for sure.

In Australia, scientists have struggled to understand how the disease reached their country – from Africa, New Guinea, or elsewhere? How did it spread from Melbourne to Queensland?

How did it infect possums, koalas, and bandicoots and fill their guts and droppings with millions of ulcer germs? How does it spread from marsupials to people?

The germ has been found in the salivary glands of some Australian mosquitoes so they are under suspicion as possible vectors. But, again, nobody knows for sure.

Luckily, Buruli ulcer has not reached New Zealand, but we must keep our eyes open for its appearance. If the disease can jump more than 3000 kilometres from New Guinea to Melbourne it could conceivably jump 4000km to NZ.