Surprisingly, one of the current areas of contention is over the identity of the organism that caused the first two historic plagues (541-c. 750, 1347-1720 or later). Within the last few years standards for methods and criteria on ancient biomolecules have been developed [1, 2]. This process will probably continue to evolve for some time considering the youth of the field.
For now, these three criteria for diagnosis by ancient biomolecules appear to have some consensus:
- Microbe specific DNA amplified and identified by more than one group
- Survival and identification of a microbe specific non-DNA biomolecule
- Biological plausibility
Collectively these criteria have been met to identify Yersinia pestis as the microbe of the historic plague. Three different teams [ 2, 4-6, 8] have amplified Yersinia pestis specific DNA from skeletal remains of ancient Europeans. One other group  has failed to amplify DNA from reputed plague victims but it is difficult to assess negative results on ancient DNA. Dancourt and Raoult  also noted that they failed to amplify Y. pestis specific DNA from specimens obtained by the this group. It is difficult to assess whether the problem was sampling error (bad luck of not picking someone who died of plague), poor cemetery choice, poor extraction methods, or other technical reasons. While Drancourt and Raoult’s groups in France have pioneered the identification of Y. pestis in skeletal remains, they have subsequently come under the heaviest attack. In support of their findings, Wiechmann and Grupe in Germany  found supporting evidence in a single 6th century grave from Bavaria. The best support of the DNA evidence is actually from Pusch’s group  in a sense because they argue that their antigen method is better than DNA amplification. In the process of showing their antigen method, they also amplify some Y. pestis specific DNA for comparison. I will come back to each of these groups in separate posts at some later date.
The second criteria has been met in the Rapid Diagnostic Test for Yersinia pestis‘ specific F1 capsule antigen developed by the Pasteur Institute of Paris and Madagascar as a diagnostic test for modern plague victims. This dipstick method is a significant advance because it is easy to use, economical and specific. It is an antigen-antibody test that works like a home pregnancy test. Two separate groups have used the dipstick method to identify plague victims in 16th-18th century skeletal remains. Pusch’s group  used both DNA and antigen testing on the skeletal remains and got positive results on both for at least two people. The one draw back to this method is that they have not proven that it will work on material older than the 16th century. If it does work on skeletal remains back to the 6th century, then it is likely that this will become the primary screening method moving forward.
This leaves biological plausibility. It is fair to say that the vast majority of those in biology and medicine find Yersinia pestis to be plausible. This plausibility is based on the signs and symptoms of a majority of the plague descriptions and observations in current epidemics of Yersinia pestis. This is not to say that mysteries don’t remain on the dynamics of the first two pandemics, because there are real questions yet to be solved.
Research on all three of these criteria will continue to bolster this evidence and learn more about the plague. Yet, the scientific evidence supports Yersinia pestis as the agent of the historic plagues.
1. Michel B Prentice, Tom Gilbert and Alan Cooper. (2004) Was the Black Death caused by Yersinia pestis? The Lancet Infectious Disease, 4, 72.
2. Michel Drancourt & Didier Raoult. (2005). Molecular detection of Yersinia pestis in dental pulp. Microbiology, 150, p. 263-264. [Available free online]
3. Michel Drancourt and Didier Raoult. (2005) Paleomicrobiology: Current Issues and Perspectives. Nature Reviews Microbiology, 3, 25-35
4.Drancourt M, Signoli M, Vu Dang L, Bizot B, Roux V, Tzortzis S, et al. Yersinia pestis Orientalis in remains of ancient plague patients. Emerg Infect Dis [serial on the Internet]. 2007 Feb [date cited]. Available from http://www.cdc.gov/EID/content/13/2/332.htm
5.Drancourt, M. et al. (2004) Genotyping, Orientalis-like Yersinia pestis, and plague pandemics. Emerging Infectious Disease Available from http://www.cdc.gov/incidod/EID/vol10no9/03-0933.htm
6.Drancourt Michel; Raoult Didier (2002) Molecular insights into the history of plague. Microbes and infection / Institut Pasteur;4(1):105-9.
6.Carsten M Pusch, Lila Rahalison, Nikolaus Blin, Graeme J Nicholson, and Alfred Czarnetzki. (2004) Yersinial F1 antigen and the cause of the Black Death. The Lancet Infectious Disease, 4, 284-284.
7.Raffaella Bianucci, Lila Rahalison, Emma Rabino Massa, Alberto Peluso, Ezio Ferroglio, and Michel Signoli. (2008) A Rapid Diagnostic Test Detects Plague in Ancient Human Remains: An Example of the Interaction Between Archeological and Biological Approaches (Southeastern France, 16th–18th Centuries) American Journal of Physical Anthroplogy, 136, 361-367.
8. Wiechmann, I & Grupe, G. (2005). Detection of Yersinia pestis DNA in Two Early Medieval Skeletonal Finds from Aschheim (Upper Bavaria, 6th century). American Journal of Physical Anthropology, 126, 48-55.
8. Bianucci et al. (2009) Plague immunodetection in the remains of religious exhumed from burial sites in central France. Journal of Archaeological Science, 36, 616-621.
9.Gilbert T, Cuccui J, White W, et al. (2004) Absence of Y. pestis-specific DNA in human teeth from five European excavations of putative plague victims. Microbiology, 150 (Pt 2), 341-354.