Category Archives: aDNA

Contours of the Black Death Cemetery at Charterhouse Square, London

Excavations for the Crossrail Extension project discovered the second major Black Death cemetery in London in 2013. This week the first peer-reviewed publication of findings from the site appeared (in press).  As a rescue excavation in the midst of a construction project, the site had to be quickly surveyed for the extent of the cemetery and this is what is contained in this publication.

This site is part of 13 acres leased by Sir Walter de Mauny from St Bartholomew’s Priory for an emergency cemetery for plague victims in 1349 AD.  The site has been used for a variety of purposes over the centuries and currently is a four acre green space called Charterhouse square. The site is graphically displayed below with the locations of later structures.

Crossrails site, London
Crossrails site in Charterhouse Square, London (Dick et al., 2015)

The initial discovery came in a shaft just to the southwest of the Charterhouse Square. There they found three layers of graves with a total of 25 bodies lacking signs of trauma and with pottery shards from 1270-1350 AD. Subsequent radiocarbon dating and aDNA analysis confirmed that they were victims of the Black Death.

The surveys conducted over just two days were able to outline the broad contours of features at the site. These included a 15th century building, a priory kitchen, a probable World War II submerged emergency water tank, and a possible ditch and bank along the cemetery that is mentioned in descriptions. They believe that a disturbed area in the southwest corner represents about 200 individual graves, although only excavation can confirm these graves. They concluded that their ability to detect medieval objects in such an intensely used urban area suggests these methods are a good option for similar future situations.

The scans also revealed some surprises. There are not as many graves as descriptions suggest should have been there, though bodies may be more dense that suggested by the scans. They also did not find any large pits of  stacked bodies. This indicates that even during the height of the Black Death, many people were still buried in individual graves. Graves were found in three phases with layers of clay-rich earth in between perhaps in an attempt to seal the graves. These scans should allow them to target future excavations to areas with a high probability of dense graves.

Reference:

Dick, H. C., Pringle, J. K., Sloane, B., Carver, J., Haffenden, A., Stephen Porter, H. A., et al. (2015). Detection and characterisation of Black Death burials by multi-proxy geophysical methods. Journal of Archaeological Science, 1–50. doi:10.1016/j.jas.2015.04.010 [In press, accepted manuscript]

Expanding the Historical Plague Paradigm

When the first complete genomic sequence of Yersinia pestis was published on October 4, 2001 the world was naturally focused elsewhere, on anthrax bioterrorism — the Amerithrax incident was then in its second week– and the September 11 attacks were just over three weeks old. As the world redeveloped bioterrorism assessments and plans, plague was placed on lists along with anthrax, smallpox and yes, ebola as agents of national security concern and response.  Although plague produced more annual cases than most agents on the category A bioterrorism list, it was placed on the list primarily based on its historical reputation and past attempts to weaponize it (also based on its reputation). Yet, in 2001 there was a fierce debate ranging among historians and others on whether Yersinia pestis was the agent of the Black Death at all.

It would take another ten years before genomics would revolutionize our understanding of the historical plague. On October 12, 2011 the first draft sequence of an ancient plague genome was published. Finally, adding to the detection of Yersinia pestis DNA tests previously done on remains, the draft sequence isolated from the East Smithfield Black Death cemetery in London solidified consensus that Yersinia pestis is the agent of the Black Death pandemic.  Meanwhile, the phylogenetic tree of Yersinia pestis had been constructed based on the genetic sequence of isolates from all over the globe. Ancient and modern Yersinia pestis genomes were opening a new window into the history of the species.

As fundamental as genomic analysis is to the new understanding of historical plague, it is a skeleton of data that is open to many different historical interpretations. Science can’t adequately explain the historic plague epidemics alone; it takes historical context. In the inaugural double issue of The Medieval Globe,  Pandemic Disease in the Medieval World: Rethinking the Black Death (open access) begins this process. The eleven articles in this issue take the genetic identification of Yersinia pestis  as the agent of the Black Death as foundational and integrate modern biological and epidemiological information into a new global Old World assessment of the history of the Black Death and subsequent epidemics. Each of these articles lays the groundwork for future interdisciplinary work between historians, anthropologists, biologists, epidemiologists and others.

In my own contribution to this issue, “The Black Death and the Future of the Plague” I discuss why plague is still important in the modern world and for our future. Plague has played an integral role in the development of the re-emerging infectious diseases paradigm and is an agent of biosecurity concern. I review the current state of plague around the world, what we have learned about plague epidemiology and transmission, and how it can be applied to historic epidemics. I also make my case for why the study of the entire history of plague is uniquely important and why the sciences and humanities must move forward together.  I hope we can engage in a discussion on these issues here in the comments section, on twitter or by email.

My own interest and awareness of the issues surrounding the study of the plague was transformed when I had the great fortune to be invited by Monica Green to participate in a session at the American Historical Association annual meeting in New Orleans, January 2013. The group of plague scholars gathered there has largely remained in contact and expanded our network into an informal working group that has enriched all of our scholarship.  No one can become fully conversant with all of the disciplines involved in the study of even one epidemic, much less the entire history of the plague.  Working in disciplinary seclusion will not produce a satisfying paradigm or widespread consensus. It takes work, patience and some tolerance of how other disciplines work, but I have found it to always be worth it. I hope you will agree.

Some references for the milestones mentioned:

Parkhill, J., Wren, B. W., Thomson, N. R., Titball, R. W., Holden, M. T., Prentice, M. B., et al. (2001). Genome sequence of Yersinia pestis, the causative agent of plague. Nature, 413(6855), 523–527. doi:10.1038/35097083

Morelli, G., Song, Y., Mazzoni, C. J., Eppinger, M., Roumagnac, P., Wagner, D. M., et al. (2010). Yersinia pestis genome sequencing identifies patterns of global phylogenetic diversity. Nature Genetics, 1–20. doi:10.1038/ng.705

Little, L. K. (2011). Plague Historians in Lab Coats. Past & Present, 213(1), 267–290. doi:10.1093/pastj/gtr014

Bos, K. I., Schuenemann, V. J., Golding, G. B., Burbano, H. A., Waglechner, N., Coombes, B. K., et al. (2011). A draft genome of Yersinia pestis from victims of the Black Death. Nature, 1–5. doi:10.1038/nature10549

Pandemic Disease in the Medieval World: Rethinking the Black Death. Edited by Monica Green. The Medieval Globe, 1 (1), 2014.

The Paleomicrobiology of Malaria Detection

Malaria is arguably one of the most influential infectious diseases in human history. Its been with us as long as we have been human, but as Teddi Setzer shows us in her recent review of detection methods, our abilities to find it in the past leaves a lot to be desired.

The standard method of looking for malaria involves searching for signs of anemia on the skeleton on the hypothesis that the anemia caused by malaria leaves these marks. This is not as clear as it might seem. There have been very few skeletal studies of modern people who have been diagnosed with malaria. There is no medical need; there are much more reliable methods of diagnosing malaria in a living person (or recent cadaver). So, it is unclear how often these lesions form in malaria patients. Other causes of anemia and even scurvy can cause the same or very similar lesions as well.  The number of malarial infections and/or relapses also effect bone changes. Plasmodium falciparium produces a short, virulent disease that may kill before bone changes develop. On the other extreme, a single P. malariae infection can relapse for life, although the anemia is not as severe.  Osteology must be correlated with other information to support the diagnosis. 

Cribra Orbitalia from Jess Beck’s blog Bone Broke

Cribra orbitalia and porotic hyperostosis are the two main indicators sought. Both are caused by bone marrow expansion in an attempt to compensate for the loss of red blood cells. Cribra orbitalia is pitting and extra bone growth in the orbits of the eyes, as seen in the photo.  Porotic hyperostosis causes pitting and thinning of the compact bone ‘shell’ that covers the cranial bones. A  correlation of nutritionally informed osteology with later epidemiology and mosquito incidence in England reviewed in a previous post shows that a convincing case can be made for malaria in ancient remains.

Detection of human genetic traits selected for by malaria such as the Duffy blood group, sickle cell trait, thalassemias, and glucose-6-phosphatase deficiency (G6PD) can with supporting information suggests that the population was once under selection by malaria. Balanced polymorphisms like sickle cell trait can remain in a population for centuries after the selection is gone (by either ecological change or by migration away from the malarious region). While there are some skeletal indicators of some hemoglobinopathies, human ancient DNA analysis would be a more secure method of diagnosis. Care has to be taken to distinguish skeletal changes made by malaria’s hemolytic anemia and the hemoglobinopathy anemias.

Ancient DNA detection of the malaria Plasmodium parasite has been disappointing. To date, only the tropical Plasmodium falciparium, that causes the most severe disease, has been detected by PCR. It is believed that attempts of detect the historically more common Plasmodium vivax have been stymied by the low parasite load in the blood.  The difficulty in finding vivax aDNA is a reminder that pathogens really do need to be in high concentrations within the sample to overcome degradation and be detected by PCR or sequencing technology. As far as I know, there have not been attempts to detect the other three human malarial parasites– Plasmodium ovale, Plasmodium malariae and Plasmodium knowlesi — by aDNA analysis.

Hemozoin crystals in the liver (Source: KMU Pathology Lab)

Modern medicine is devising an ever expanding array of tests for malaria diagnostics and prognostics. However, most of these tests all require fresh (soft) tissue or blood. Immunological methods have not been applied to malaria in archaeological material yet. The most promising detection method for malaria among the newer diagnostics is the detection of the iron containing waste product of the Plasmodium parasite hemozoin. When the parasite feeds on hemoglobin in the red blood cell, toxic iron waste products are processed into the biocrystal hemozoin and excreted into the tissues. In patients with reoccurring or multiple malaria infections, hemozoin will stain their bone marrow black and can be found in liver, spleen, brain and lungs. It can be detected microscopically (as seen above) or by mass spectrometer. Although some other blood parasites also excrete hemozoin, they can be distinguished from the malarial product. 

Despite the advances in diagnosis for existing malaria patients taking advantage of new methods and technologies, archaeological detection has not enjoyed the same success. Building a case for malaria in the past, must rely on an array of data with knowledge of ecology, vectors, and nutritional status of the population in addition to osteological markers of anemia. Hopefully, the detection of hemozoin will eventually be the key to opening up biological studies of malaria in the past. If hemozoin can identify malaria victims, then perhaps focusing the ancient DNA work on hemozoin positive remains will be more successful breaking through the firewall to malaria’s evolution and historical epidemiology. 

 Source:

Setzer, T. J. (2014). Malaria detection in the field of paleopathology: A meta-analysis of the state of the art. Acta Tropica, 140, 97–104. doi:10.1016/j.actatropica.2014.08.010 (open access early editionfinal edition)

See also Jess Brek “Porotic Hyperostosis and Cribra OrbitaliaBone Broke, March 2014.