Analysis of medieval skeletons from two sites, one in Chichester and another in Raunds Furnells, has identified the presence of Mycobacterium leprae DNA – signs of leprosy in medieval England.
Also known as Hansen’s disease, leprosy is a slowly progressive infection that produces lesions and damages the nerves. It is caused by the bacteria Mycobacterium leprae or, in a minority of cases, M. lepromatosis. There are several different strains of M. leprae, currently grouped under six main branches that reflect their geographical distribution. A new study in the Journal of Archaeological Science (https://doi.org/10.1016/j.jas.2019.105035) has shed light on the presence of leprosy in medieval England and the distribution of different subtypes of the disease – as we will explore in Science Notes.
Leprosy is one of the oldest diseases ever known to have affected human populations. It was, however, relatively uncommon in Europe until the medieval period. Its prevalence in Britain appears to have peaked in the 13th century AD, declining again by the 16th century. The disease only causes skeletal changes in around 5% of cases, and the lesions produced can be ambiguous, so the detection and sequencing of M. leprae DNA is extremely important in identifying leprosy in the archaeological record.
The recent study looked at six samples taken from skeletons curated by the University of Bradford that had been excavated at two sites in England. Four were from the cemetery of the Hospital of St James and St Mary Magdalene, Chichester, which was founded c.AD 1118 and housed people with leprosy until it was dissolved in AD 1442, when the prevalence of leprosy in the UK declined. The other two were from a late Anglo-Saxon churchyard cemetery at Raunds Furnells, Northamptonshire, which was in use from the mid 10th to the mid-12th centuries AD (see CA 106). The skeletons chosen all displayed pathological signs that could be indicative of leprosy.
Samples of bone were taken from the skeletons, decontaminated, and then crushed to a fine powder. DNA was extracted from 0.2g of bone powder, and a method called polymerase chain reaction (PCR) was used to amplify the small DNA samples until there was a large enough amount for it to be studied in detail.
The DNA samples were then screened for the presence of M. leprae DNA and it was discovered that samples from three skeletons – C21 and C48 from Chichester and R5046 from Raunds Furnells – contained the DNA of the bacterium. All three skeletons also had extensive osteological indicators of leprosy. Of the other skeletons, which tested negatively for the presence of M. leprae, one had significant osteological indicators of leprosy and was in very poor condition, so it is possible that the failure to detect the DNA was result of biomolecular degradation. However, the other two skeletons lacked both the M. leprae DNA and some physical indicators, making a diagnosis of leprosy less likely.
A technique called Illumina sequencing was used to study the samples from the thee positive skeletons in more detail, allowing the M. leprae
strains to be assigned specific subtypes. The strain identified in the skeletons from Chichester (C21 and C48) was of a subtype called 3I. This is consistent with M. leprae strains previously identified at other medieval sites in Britain and Ireland, which have been assigned subtypes 2F and 3I.
Interestingly, the DNA in the skeleton from Raunds Furnells (R5046) was found to be of subtype 3K, which has never been identified in Britain before. In modern M. leprae, subtype 3K is associated with East Asia, and in ancient specimens it has been found in one Turkish skeleton (8th-9th century AD), three from Hungary (7th-10th century AD), and one from Denmark (11th-13th century AD). The skeleton from Raunds Furnells is similar in date, but is the most westerly example yet found.
The unexpected presence of subtype 3K in England raises questions about how this individual contracted it. It has previously been suggested that movement along the Silk Route was responsible for bringing subtype 3K to eastern Europe from its supposed centre of origin in East Asia. Travel between Britain and continental Europe was relatively common during the Anglo-Saxon period up to the 10th century, especially by educated clerics, and the route from western Europe to reach the Holy Land passed through Hungary, Serbia, and Bulgaria. It is possible that this strain of the disease was transmitted to England by someone travelling through eastern Europe on that journey, or that the individual had travelled to continental Europe or Asia themselves and caught the disease there, before returning to England.
The results of this project support existing knowledge about leprosy in medieval Britain and raise intriguing questions about mobility and the spread of different subtypes of M. leprae in this period.