An outbreak of Buruli ulcer, an infectious disease that causes serious injury to the limbs, is spreading in Australia. The causes of this progression remain unknown.
When she noticed a big pimple on her ankle a few months ago, Jacinta Mazzarella thought she was bitten by an ugly mosquito while vacationing in Melbourne with her family. But in a few weeks, the skin of this young 18-year-old Australian dancer began to break down and a hole the diameter of a coin appeared. “I had to stop working for five months and I can not dance anymore,” she says. Like many Australians in recent times, Jacinta Mazzarella has been contaminated by the “flesh-eating bacteria”, as this mysterious and virulent disease is sometimes called.
Buruli ulcer, also known as Bairnsdale ulcer or Daintree ulcer, is a tropical disease caused by the bacterium Mycobacterium ulcerans. In the same family as tuberculosis and leprosy, it causes tissue damage and inhibits the immune response. This often starts with a painless nodule or discolored plaque on a limb or on the face. The immunosuppressive power of mycolactone at the local level allows the disease to progress insidiously without pain or fever. In about four weeks, the ulcer evolves into a wound up to several centimeters in diameter with tissue necrosis, sometimes affecting the bone, resulting in deformity of the limb. The only treatment possible is the administration of an antibiotic combination for at least four weeks. But this is not always effective and the disease is often diagnosed at an advanced stage, with sometimes irreversible lesions that can even require amputation.
According to the WHO, 2,209 cases were recorded in 13 countries in 2017, mainly in African countries (Benin, Cameroon, Ivory Coast …) but the recrudescence is particularly significant in Australia. In the southeastern state of Victoria, more than 330 patients were registered in 2018, a four-fold increase in four years. Several cases have also emerged in the state of Queensland further north. Not only does the disease seem to be spreading, but it is also becoming more virulent, the authorities report.
The causes of the epidemic remain largely mysterious. The disease would be transmitted during direct contact with contaminated water or soil, or during trauma (injury, cut, etc…). Some evoke a transmission via mosquitoes, but this theory has not yet been confirmed. Propagation would also be promoted by animals (opossums, koalas, dogs and domestic cats) acting as “healthy reservoirs” for the bacteria.
According to WHO, Mycobacterium ulcerans needs a temperature of between 84 °F and 92 °F to grow; which explains why it is “preserved” relatively well in the environment (for example, the bacillus of tuberculosis needs a temperature of 99 °F). No preventive measures have yet been found, which leaves doctors quite helpless in the face of the phenomenon.