Rewriting leprosy's global expansion

The ancient scourge known as leprosy likely originated in either East Africa or Central Asia and extended its reach in a pattern mirroring human migration, according to a new analysis of its bacterial agent's unusual genetic fingerprint.

Led by researchers at the Pasteur Institute in Paris, the study suggests the disease reached West Africa and North America through infected explorers, traders or colonists within the past 500 years, and that it infiltrated the Caribbean and South America via the slave trade in the 18th century.

"Colonialism was extremely bad for parts of the world in terms of human health," co-author Stewart Cole said in a news release accompanying the study in the journal Science.

Recorded in China, India and Egypt as early as 600 BC, leprosy attacks nerve and skin cells, resulting in permanent disabilities if left untreated. The bacterial culprit, Mycobacterium leprae, has proven a difficult study subject because of its extreme sluggishness and inability to grow in anything other than humans, mouse footpads and the nine-banded armadillo.

Through genetic analysis, however, Monot, Cole and their co-authors found that seven M. leprae strains from patients in 21 countries were nearly identical, suggesting the disease spread from a single clone whose DNA sequence has remained remarkably stable for centuries.

To chart the disease's global expansion, the team analyzed a genetic landmark known as a single nucleotide polymorphism, or SNP. This uncommon variation in DNA letters - a CTC sequence at one site instead of TTC, for example - revealed that all of the bacterial isolates could be divided into four groups.

Alan Templeton, a biology professor at Washington University in St. Louis who wasn't involved with the study, said the reliance of the bacterial parasite on humans has, in a sense, coupled the parasite's evolution with ours. He cautioned, though, that data from many sources will be required for a clear picture of human migration.

Apart from the historical applications, the organism's remarkable stability could be its Achilles heel if researchers can demonstrate the effectiveness of a vaccine against any of the bacterial strains. "If a vaccine arrives," Monot said, "the vaccine would be universal."

•	Rewriting leprosy's global expansion Newsday (New York), Friday, May 13, 2005 Byline: Bryn Nelson, Newsday staff writer