It has long be thought that mercury was one of a number of treatments used for leprosy in the Middle Ages. A new study has tested this hypothesis by examining the mercury levels contained in the dental calculus build up on the teeth of remains taken from the burial grounds of leper hospitals and comparing it to samples from elsewhere. The remains from leper hospitals showed levels of mercury well above the norm - confirming the hypothesis that treatment likely included mercury.
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| Monks suffering from leprosy receive instructions from a bishop. Omne Bonum, (BL Royal 6 E. VI,) |
There are a number of factors which need to be kept in mind when examining leprosy in the Middle Ages and a key one is the definition of disability in the Middle Ages was not the definition we use today. In modern clinical definitions the term 'leprosy' refers exclusively to Hansen's Disease, caused by either Mycobacterium leprae or Mycobacterium lepromatosis. However in the Middle Ages, leprosy was more of a catch all term for disease causing rough, scaly skin or tissue necrosis. As such not all people living in medieval leprosaria or 'leper houses' were suffering from Hansen's Disease - however most of those who were buried in the associated cemeteries were. Assigning a likely diagnosis of leprosy in a set of remains requires a number of criteria to be fulfilled. Per the work of Tony Waldron in both Palaeopathology and Operational Definitions for Palaeopathology [Clarifications for non-specialists in square brackets mine] -
(1a) Facies leprosa [a characteristic bone change]
(1b) Destruction of small bones of the hands or feet, starting distally and proceeding proximally. [Beginning with the extremities and progressing inwards towards the centre of the body].
(2) Osteomyelitis, particularly of the bones of the feet
(3) Charcot joints [Fragmentation of the bones and joints, particular in the feet ].
In this study samples were taken from the dental calculus and them compared to reference samples from non-leprosaria burials and showed much higher levels of mercury.
Mercury has long been associated with medicinal usages - even after its dangerous toxicological profile was well known - and is not exclusively associated with the Middle Ages - having been used extensive in the 18th and 19th centuries - including as an (ineffective) treatment for syphilis.
In my view this study is interesting what it confirms - i.e. that the medieval medical recipes which included mercury may well have been using the element itself rather than this being a case of misapplication or a confusion between modern and medieval terminology which is an unfortunate pitfall of researching medieval medicine. It also validates the idea that dental calculus can be used to identify medicinal compounds used by individuals in the Middle Ages - which opens up new potential directions in research into medieval pharmacology. The full study can be read here.