Leprosy's Missing Link

Fig.1. A photo-micrograph of Mycobacterium leprae, the pathogen which causes leprosy (Hansen’s disease) taken from skin lesions of an infected patient. The red rods are M. leprae bacteria (Credit: CDC, 1979)

More often found in the Bible than in modern vernacular, leprosy has been treated with fear and social stigma for centuries. Leprosy, also known as Hansen’s disease, still exists today in small pockets around the world but is curable and not very contagious. New molecular techniques have allowed some scientists to track the causative agent Mycobacterium leprae through time and space to hopefully inform modern health care professionals on possible treatment guidelines. A recent study published in PLOS One may not only shed light on the pathogen’s evolution but also show how human migration can be traced through disease.

From Scandinavia to Great Britain

An international team of researchers led by the University of Leiden found evidence of leprosy in a 5th- to 6th-century male skeleton excavated in what is today Essex, England. Isotope analysis revealed that the man most likely migrated from southern Scandinavia. Some of the characteristic leprosy lesions were found on the bones, but molecular tests were required to determine the presence of M. leprae in the individual. Further genotyping of the pathogen identified the isolate as part of a lineage of bacterial strains called 3I.

These results are part of a wider understanding of how leprosy spread and evolved. Strains from the 3I lineage of M. leprae have also been found in burials from medieval Scandinavia and southern Great Britain, matching the probable origin of the Essex individual. This suggests that the man brought leprosy with him when he migrated to Great Britain. Additionally, 3I strains are found in modern times in the Americas.The Essex case could be part of the missing link in the spread of leprosy from Europe to the New World.


Fig.2. The island of Spinalonga in Lasithi, Crete. This was formerly a Venetian fortress and then operated as a quarantine for those suffering from leprosy from 1903 to 1957. Such practices of quarantine were common before health efforts began to address the disease and social stigma its victims experienced (Credit: via Wikimedia Commons)

Human migration and disease

The Essex case was highly localized and on an individual scale, but previous research has shown that changes in pathogen genomes can point to the movement of humans over time. For example, a 2013 study compared the sequences of 31 herpes simplex virus type 1 (HSV-1) strains from around the world. The strains’ genetic differences mapped with HSV-1 mutation rates supported current anthropological data about human migration over thousands of years. Because both M. leprae and HSV-1 co-migrate and evolve with their hosts, they offer an effective proxy of migration, especially in lieu of other archaeological materials.

Ancient skeletons and disease genome databases are useful resources for the study of disease, but current health efforts must stretch beyond these tools. Collections for health researchers now include everything from those in museums for tracing pathogens in animal reservoirs to social media sites for large-scale data analysis. Additionally, the connection between human migration and disease is more important than ever with the increased ease of travel and the import of pathogens to new and untouched lands. For now, research of skeletons like the Essex man informs our understanding of relevant disease issues and provides an exciting opportunity for mapping ancient migration.



References:

Gushulak, B. D. & MacPherson, D.W. (2004). Globalization of Infectious Diseases: The Impact of Migration. Clinical Infectious Diseases, 38 (12): 1742-1748. doi: 10.1086/421268.

Inskip, S.A., et al. (2015, May 13). Osteological, Biomolecular and Geochemical Examination of an Early Anglo-Saxon Case of Lepromatous Leprosy. PLOS ONE, DOI: 10.1371/journal.pone.0124282

Schuenemann, V.J., et al. (2013, July 12). Genome-Wide Comparison of Medieval and Modern Mycobacterium leprae. Science, 341: 179-183. Retrieved from https://www.sciencemag.org/content/341/6142/179.full.pdf.

Glossary

isotope analysis
The identification of different types of atoms of the same element. These variants are called isotopes and their distribution or ratio can be affected by weather patterns and environment, such as precipitation. Isotope analysis can determine where an individual is from by matching the isotope distribution with diet or weather in a certain area.
genotyping
The process of determining genetic variants in an individual’s genome.
bacterial strains
A genetic subtype of a species of bacteria.