The study of the DNA of diseases is becoming increasingly popular to understand how it affected people in the past, how the disease evolved, and whether its modern equivalents are similar. Genomic studies of different variations of the plague have been in the news over the past few years. A recent study of the Justinian plague aided in better understanding this variant of the plague and its relationship to the Bubonic Plague and modern variants of the disease. Another example is the analysis of the DNA of brucellosis in an Albanian population. This study helped identify two individuals with the disease and better interpret how the disease spread. While DNA studies do have their limitations, especially in ancient remains, they can be helpful and revealing.
Leprosy is almost always portrayed as a historic disease. It is most prevalent in texts like the Bible, where the physical deformation of the body is equated to spiritual uncleanliness. In more popular media, leprosy is seen in Monty Python’s Life of Brian where an ex-leper begs for money after Jesus cleansed him of the disease. However, it is most well known for its virulence during the High Middle Ages in Europe. Leprosy has been well studied in physical remains from the 11th to 16th centuries throughout Northern Europe. Leprosarium or leprosy hospitals have been excavated from this period and revealed how individuals in this period were treated. A new study by Roffrey and Tucker (2013) argued that individuals infected were not the social outcasts they had been portrayed as, but rather were taken care of in special communities and were well-provided for. Further, many leprosy hospital sites seemed to have served anyone in need including those with pathologies, deformities and even pilgrams. However, it remains prevalent among certain developing nations, and new drug resistant strains of the disease have made it increasingly hard to eradicate. (For more on modern cases, see this article on a recent case from Ireland)
A new study by Schuenemann et al. (2013) compares the genomic sequences of modern and medieval strains of Mycobacterium leprae, more commonly known as leprosy. Leprosy begins to appear historically in Europe during the early Medieval period, and peaks in prevalence from the 11th to 16th centuries. At the end of the 16th century, the disease had for the most part vanished from this area. However, it remains epidemic among nations in the developing world, and only recently has ben reduced to manageable cases. In order to better address the modern continuation of the disease, Schuenemann et al. (2013) propose that comparison of modern to medieval strains of the bacterium may reveal why it so rapidly disappeared in Europe and how to address the modern equivalent.
The medieval sample consisted of 22 individuals taken from cemeteries with identified leprosy victims based on skeletal deformation. The remains were taken from cemeteries in Denmark, Sweden and the UK. These three countries have well documented cases of medieval leprosy based on the presence of pathologies within the bone and burial at leprosaria. While only a small number of cases of leprosy develop bony reactions, it can be easily identified in skeletal remains by the presence of new bone formation in the skeleton and destruction of bone in the extremities and face (For more on the bioarchaeology of leprosy, see this post). Analysis of the pathogen’s DNA revealed that it was fairly intact in the remains, a surprise to the researchers given the age and loss of information that usually occurs. Of the individuals tested, five had pathogen DNA that was complete enough to perform a complete analysis of the genomic sequence. These were compared against pathogen DNA from 11 modern cases of leprosy from India, Thailand, Brazil and the USA.
They found that the modern equivalents of leprosy found in the Middle East are comparable and potentially related to the strain of leprosy found in Medieval Europe. However, the strain found in the Americas is from a different version of the Medieval European leprosy, indicating that the modern ones are different. Knowing the relationships between strains of leprosy also aids in understanding the spread of the disease. The knowledge that the Middle Eastern leprosy stems from the European variant supports the conclusion that the disease first spread to this region during the crusades. It also supports the conclusion that leprosy was not endemic to the Americas, but rather spread during European colonization.
From this analysis, they argue that leprosy did not drastically decline in Europe due to a loss of virulence or the disease dying out. Since Medieval leprosy appears to be the ancestor to modern leprosy, the decline in Europe is more likely related to changes in urban environment, public health and community immunity (BBC estimated that 95% of the European population is immune). Given the success of this analysis, they argue that future studies should attempt to trace the origins and spread of the disease in more detail. Currently, this doesn’t aid in determining how to wipe out the modern strains, but it does show potential for learning more.
Schuenemann, V., Singh, P., Mendum, T., Krause-Kyora, B., Jager, G., Bos, K., Herbig, A., Economou, C., Benjak, A., Busso, P., Nebel, A., Boldsen, J., Kjellstrom, A., Wu, H., Stewart, G., Taylor, G., Bauer, P., Lee, O., Wu, H., Minnikin, D., Besra, G., Tucker, K., Roffey, S., Sow, S., Cole, S., Nieselt, K., & Krause, J. (2013). Genome-Wide Comparison of Medieval and Modern Mycobacterium leprae Science DOI: 10.1126/science.1238286