At the finish of October, a collection of scientists from Canada, Germany, and the United States published papers that marry the fields of genomics, public health and archeology.
Led by Johannes Krause at the University of Tübingen, Germany, and Hendrik Poinder of McMaster University in Canada, the side report they were able to series the full genome of the bacteria accountable for the Black Death, a plague that swept from side to side Europe from 1347-1351, killing anywhere between 30 and 50 percent of the inhabitants.
The findings resulted from DNA extract from several teeth recovered from a plague pit in London. Victims in London pile up so quickly in the 14th century — some 200 a day at the plague’s height — that church officials organized mass graves, or plague pits. DNA second-hand in this study came from East Smithfield in the heart of London’s financial district — now actually under the old Royal Mint structure.
The technique obtainable for sequencing DNA are now so sensitive that it’s likely to analyze DNA from very old sample, as long as there’s recoverable DNA present. Known as paleogenomics, work in the area got started in a quest to uncover the secrets of Egyptian mummies and has since been used on samples from prehistory, particularly the wooly mammoth and, more recently, the Neanderthal. Those sample were tens of thousands of years old, whereas, in this case the teeth from which the bacterial DNA was recovered only dated back about 660 years. However, it’s more difficult to rebuild the sequence of an ancient bacterial genome than a mammal, as bacterial genomes are much lesser, and contamination from soil bacteria is harder to filter out.
Formative the precise cause of a plague that happen nearly 700 years ago is something that’s only recently become possible since the advent of genomics – and particularly the development of Next Gen technologies that do not rely on DNA intensification with polymerase chain reaction techniques that can increase contagion. For some time, researchers thought that the pestilence was caused by a bacterium called Yersinia pestis, but y. pestis is still with us, and although it causes bubonic and pneumonic plagues, such outbreaks don’t have nearly the same severity (or even the same range of symptoms) as the Black Death, leading to growing doubts among some historians and scientists as to the true pathogenic culprit. Historians have been able to chart the route of the disease through historical records; the contemporary accounts of symptoms, giving us an idea of a victim’s fate once infected; and the burial records, which give us an idea of the speed of broadcast from town to town and the high mortality rates once the plague arrived.
Armed with the genome sequence for Y. pestis recovered from the pestilence pit, the researchers were able to use it along with genome sequence of current Y. pestis strains to create a phylogenetic tree, mapping the development of the pathogen from then until now. The analysis puts the Black Death Y. pestis near the root of this evolutionary tree, suggesting that Black bereavement was the first widespread encounter that humans had with this bug.
Comparative analysis of this ancient version of Y. pestis with current strains showed that there are few genomic clues as to why it was so much deadlier in the 14th century, as there has been surprisingly little change to the bacteria’s genetic code. in its place, the authors suggest that the terrible toll of the Black Death was probably due to a number of other factors. The poor hygiene and public health of the time was probably a factor, as well as the genetic makeup of the population. It’s likely that many of these victims had greater susceptibility to the ailment, and their deaths increased the proportion of the population who were best able to resist, possibly explaining why more recent outbreaks have not been nearly as terrifying.
And lest this seem like an academic study of some historical event, it’s not. Other researchers recently reported that a strain of Escherichia coli that caused a particularly nasty outbreak of foodborne illness in Germany earlier this year contained DNA sequence from the original plague bacteria. Bits of the Black Death may still lurk about, to come to make us sick.