The pathogen responsible for leprosy was discovered in 1873 in Norway, squashing previous assumptions about its cause. The earliest written mention of leprosy, one of the oldest-known pathogens to plague humans, appeared in 600 B.C. in China. Historical records show it plagued ancient Greek, Egyptian and Indian civilizations. In 2009, DNA analysis of a first-century man’s remains found in a Jerusalem tomb provided the earliest proven case of leprosy.
Now, DNA sequencing technology has provided clues about the evolution of the bacteria itself. Using well-preserved DNA samples from ancient skeletons, an international team of researchers has sequenced the genome of the pathogen Mycobacterium leprae as it existed in medieval times.