Europeans and North Africans then spread Leprosy to West Africa, and the slave trade brought the disease from West Africa to the Caribbean and South America, the study suggests. Europeans also introduced leprosy to North America.
"Colonialism was extremely bad for parts of the world in terms of human health," said Cole.
The disease, caused by Mycobacterium leprae, primarily affects the skin and nervous system, particularly the limbs and digits. It's not especially contagious, as people once widely believed, but it can cause permanent disability and disfigurement and is still a source of social stigma. The disease is treatable with a combination of antibiotics.
The bacterium has long puzzled researchers because its genome is filled with an unusually high proportion of damaged, nonfunctional genes. This is probably why it grows exceedingly slowly, making it difficult for researchers to study because they can't grow it in culture. In fact, M. leprae only lives in humans and in armadillos (which might have acquired the bacterium by eating infected human cadavers), and it can also grow in the footpads of mice.
Cole and his international research team compared the genomes of seven strains of M. leprae taken from patients around the world and then grown in armadillos until the samples were large enough to analyze. They focused on genetic sequences known to be dynamic -- to move around, copy themselves or disappear -- and thus most likely to reflect evolutionary change, but found strikingly little variation.
Next, the researchers looked for mutations known as "single nucleotide polymorphisms" or "SNPs," which are substitutions of single nucleotides or "letters" at a specific spot in the genome. They found only three spots where useful SNPs occurred.
"Finding so few SNPs is pretty unusual. It's the least number of SNPs I'm aware of in any bacterium," Cole said.
At each of the three SNP locatio
Source:American Association for the Advancement of Science