June 14, 2013
Uncovering The History Of Medieval Leprosy With Genomics
Lee Rannals for redOrbit.com — Your Universe Online
Scientists are using thousand-year-old remains to help reconstruct the genomes of the medieval leprosy pathogen and uncover the history of the disease.
Researchers wrote in Science magazine about how they used the remains of skeletons to successfully reconstruct a dozen medieval and modern genomes of the leprosy-causing bacteria Mycobacterium leprae. They were able to create a genome from archaeological finds for the first time without having to resort to a reference sequence.
Leprosy is a very infectious disease that was widespread in Europe until the Middle Ages. People who had the disease were isolated in colonies specifically built for them in order to quarantine them from the rest of humanity. Today, the disease is found in 91 countries around the world and infects more than 200,000 people each year. Scientists wanted to use five medieval skeletons to help reconstruct the history of the disease.
The team compared the European medieval M. leprae genome with those of the seven biopsies and four additional modern bacteria strains. They observed all M. leprae strains have a common ancestor that existed less than 4,000 years ago. The genome-wide comparisons suggest unusually minor changes of the bacteria's genetic material within the last 1,000 years, which had no effects on the virulence of the pathogen. This suggests the end of the leprosy epidemic was influenced by other factors like improved social conditions during the Middle Ages.
The researchers were able to demonstrate that a form of M. leprae can currently be observed in the Middle East. Another medieval strain from Europe has striking similarities to bacteria currently identified in armadillos and leprosy patients in North America.
A larger amount of pathogen DNA was seen in the examined skeletons than is usually found in contemporary patients. The team said this phenomena is due to the circumstances that the bacterial DNA probably decomposes very slowly as a result of the extremely thick cell wall of the leprosy bacterium, enabling its accumulation in the skeletons over time.
"This makes it possible that certain forms of bacterial DNA remain preserved above the maximal age for mammalian DNA, which is approximately one million years", stated Johannes Krause, a professor at University of TÃ¼bingen. "Thus, it should be possible to trace the disease back to its prehistoric origins."
The DNA from a skeleton in Denmark of a 25-year-old woman enabled the assembly of an ancient pathogen from scratch for the first time without comparison.
"We have contacted the Danish colleagues who provided us with the important skeletons for the investigation. The DNA was extracted from the teeth of the lepers and subsequently subjected to a first molecular feasibility test," said Ben Krause-Kyora, of the Institute of Clinical Molecular Biology at Kiel University.