There is little doubt that the bacillus originated in East Africa - Stewart Cole will examine this hypothesis in a future study - and then mutated into the four different strains. "The results of our analysis are surprising," says Cole, "the difference between the different strains is very small. It is one of the most stable organisms ever observed, even if half of its genome is dead." There are only around a hundred different variations between the DNA of two different strains, whereas with HIV or the flu there may be thousands of difference mutations.

In the case of HIV, mutations are so frequent that it is almost possible to say whether a person was infected in Geneva or in Lausanne," explains Stewart Cole, "but in the case of leprosy, the most we can do is place the infection on a continental scale." But this is not bad news. Frequent mutation by a bacterium often leads to disturbing resistances to antibiotic treatments, such as with tuberculoses. But a more stable bacillus responds more efficiently to treatment regardless of the strain. "Resistant cases are extremely rare for leprosy."

Yet the disease remains a persistent public health issue in certain regions in India and Brazil. Currently, more than 700,000 people are infected world-wide and the length of treatment of at least one year can complicate its application. We have not yet head the last from Mycobacterium leprae, but public health politics, spurred on by work done by the likes of Stewart Cole and his scientific team, could put an end to the common history between leprosy and its unwilling human host.

For more information:

The scientific article in Nature Genetics: nature/ng/journal/vaop/ncurrent/full/ng.477.html

Source: Ecole Polytechnique Fdrale de Lausanne