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11th-14th centuriesPeer-reviewed · 2 sourcesWell documented

Leprosy Peaks in Medieval Europe, Then Mysteriously Recedes

Mycobacterium leprae genomes from an English hospital cemetery capture a disease at its medieval height, before it faded for reasons still not fully explained

On the timeline · around 11th-14th centuries · Medieval PandemicsMedieval PandemicsOld World Diseases, New World CollapseLeprosy Peaks in Medieval Europe, Then Mysteriously Recedes600 CE700 CE800 CE900 CE100011001200130014001500

Quick facts

Pathogen
Mycobacterium leprae
Peak period
11th to 14th centuries CE
Key site
St Mary Magdalen leprosarium, Winchester, England
Last British case
Died in Edinburgh Infirmary, 1798
Cause of decline
Not genetic weakening of the bacterium; possibly rising tuberculosis mortality and changing living conditions

What happened

Leprosy, caused by the slow-growing bacterium Mycobacterium leprae, had been present in Britain since at least the 4th century CE, but it became far more common between the 11th and 14th centuries, tracked by a surge in dedicated leprosy hospitals called leprosaria built to isolate the afflicted. Researchers sequenced M. leprae genomes from two skeletons, radiocarbon dated to 955-1033 CE and 1020-1162 CE, excavated at the St Mary Magdalen leprosarium near Winchester, England; both carried a lineage still found in modern leprosy cases, and both individuals showed the bone damage to the face and limbs characteristic of advanced infection. From the 14th century onward the disease declined sharply across Europe, and leprosaria were abandoned or repurposed; the last recorded case in Britain died in an Edinburgh hospital in 1798.

Why it matters

The decline was not caused by the bacterium evolving into a weaker form, the genomic evidence rules that out directly. Researchers instead point to competing causes: rising tuberculosis, which may have killed leprosy-susceptible people before the slower disease could progress, and gradual shifts in living conditions that reduced the extended close contact leprosy transmission requires. The case shows that a disease can vanish from a population for reasons other than the pathogen itself changing.

How we know

Ancient DNA recovered directly from skeletal remains at a documented leprosy hospital, radiocarbon dated and genetically sequenced and published in BMC Genomics, gives a rare direct genetic snapshot of a medieval epidemic rather than relying on written accounts alone.

Sources

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