Wednesday, September 7, 2011

Black Death revealed and how research leads to preparedness

Yersinia pestis
The 1348 Black Death plague was one of the worst pandemics in human history; it killed about a third of Europe's population (30-50 million) in only five years. Recent scientific advances have allowed anthropologists to identify and study the bacteria responsible, a now extinct strain of Yersinia pestis.

DNA testing on the skeletons of 109 plague victims, unearthed in a medieval London mass grave, reveals part of the same gene sequence as the modern bubonic plague, despite its different attributes. The modern strain still causes about 2,000 new cases of bubonic and pneumonic plague each year.

Rather than using polymerase chain reaction (PCR), the common genetic technique used for forensics and DNA testing, scientists used very new techniques: targeted enrichment and high-throughput sequencing. These techniques allow researchers to reconstruct long sequences of ancient, damaged DNA that have degraded over time. It's like creating a window back in time, though on a miniscule scale.

Science has taught us much about transmission and containment methods, but this does not answer all of the questions about why the 14th century Black Death plague was so virulent. Fleas commonly carry Y. pestis from host to host, and the jump from rats to humans is often a short one. However, that transmission method doesn't account for such rapid spread, despite lack of public health knowledge. Could the strain have combined with another pathogen to achieve such remarkable virulence? Researchers are hoping to tackle the answer to that question next. To do so, they will attempt to sequence the entire Black Death Y. pestis genome.

I am constantly amazed at how rapidly expanding scientific technologies allow us to gather information that would not have been accessible a mere handful of years ago. For example, when I started researching the 1918 Influenza Pandemic, scientists had not yet reconstructed the virus. In an effort to advance preparedness, CDC scientists completed the reconstruction in 2005.

Why is it important to reconstruct a virus from the past? The work provides information about the properties that contributed to the exceptional virulence of that particular virus strain. This information is critical to evaluating the effectiveness of current and future public health interventions, which can be used when a 1918-like strain reemerges, either naturally or through deliberate release. To gain a sense of what could happen in such a flu pandemic scenario, you might want to read Dormant, which is still scheduled for release in early 2012.


  1. There was some thought that the particular strain in this outbreak lead to more of a Pneumonic Plague than Bubonic. Pneumonic is an airborne form of this disease and leads to much higher infection and mortality rates.

  2. Becky: Thank you for the reminder that the Black Death plague could have been airborne. That would indeed have been particularly deadly, considering the complete lack of understanding about disease transmission at the time.