European colonialism and the slave trade probably played a key role in the spread of leprosy, research suggests.
Leprosy is still common in the developing world
The disease appears to have originated in East Africa, and spread to Asia and Europe before reaching West Africa, and then the Caribbean and South America.
The findings are based on a genetic analysis of different strains of the bacterium which causes leprosy.
The international study, led by the Pasteur Institute in Paris, is published in the journal Science.
It is hoped the findings will help public health experts better understand how leprosy is spread - and thus track the disease more effectively.
Primarily affects the skin and nervous system, particularly the limbs and digits
Can cause permanent disability and disfigurement
Treatable with a combination of antibiotics
Better understanding of the genetics of the disease might also help improve treatment, as it could enable doctors to pin down whether a patient has a new infection, or a recurrence of a previous infection.
One of the oldest known human diseases, leprosy is still a significant problem in parts of the developing world. Around 500,000 new cases were detected in 2003.
Caroline Ash, senior editor at Science, said: "The better we can understand this pathogen's genome and the subtle differences among its various strains worldwide, the better position we will be in to ultimately eliminate the disease."
The researchers scanned the genetic material of 171 samples of Mycobacterium leprae - the bacterium that causes leprosy - from 21 countries across five continents.
They looked for tiny variations known as single nucleotide polymorphisms (SNPs), which can help them to trace the genetic lineage of an organism.
The analysis showed SNPs were rare, suggesting M. leprae is genetically stable, and has hardly changed down the centuries.
But the researchers did find four distinct types of SNP.
Type 2, predominant in a small region of East Africa and Central Asia, is the rarest and oldest, the scientists believe.
Type 1, present in Asia and the Pacific region, appears to have migrated east, while type 3, seen in Europe, North Africa and the Americas, is the form that migrated west.
The most recently evolved, type 4, is predominant in West Africa.
Because type 4 leprosy is more closely related to type 3 than it is to either type 1 or 2, the researchers concluded that North Africans or Europeans probably brought the disease to West Africa, before the slave trade spread it to the Caribbean and South America.
Dr Stewart Cole, who worked on the study, said: "Colonialism was extremely bad for parts of the world in terms of human health."
Previously, it had been thought leprosy originated in the Indian subcontinent and was then introduced to Europe by Greek soldiers returning from the Indian campaign of Alexander the Great.