Stefan Milo put out this video about the Black Death today. He got me thinking,
New genetic research shows the Yersinia pestis bacteria
appeared many different times on the Eurasian steppes and then swept west over
Europe. These strains were unique and
seemed to be spontaneous.
These are some of the questions raised by the research:
What was the reservoir for Y pestis. It lives in fleas now, but not then. They can’t find an animal reservoir.
Why were there so many different strains that didn’t survive?
Why was it suddenly so much more virulent?
You can probably guess my answer.
There was no animal reservoir. Yersinia pestis evolved from Y. pseudotuberculosis. Y. pseudotuberculosis lives in the soil and on vegetables. Occasionally, as humans would forage through the landscape they would disturb the soil or eat infected food. It causes intestinal infections in humans, but they are usually mild.
However, the Yersinia family of bacteria have a number of
interchangable genetic sequences.
Plasmids and DNA fragments inherited from other species. They recombine often to create strains with
varying virulence. I assume that this
accounts for the sporadic isolated outbreaks.
The virulence factor for Yrsinia bacteria reside on one kind of fragment. It codes for a group of iron extracting molecules. The more iron it gets, the more deadly it is….
See where we’re going?
Porphyromonas gingivalis gjngipains are molecules that
extract iron from the blood. They float
around until they find some hemoglobin, and they combine with it and release the
iron.
A virulent strain of Y. pseudotuberculosis would clearly thrive in a host infected by PG. And I bet over time it mutated to live in the blood rather than the intestines. This is what took it to the next level.
There were already well established long range trade
routes. Of course it worked it way back
to the steppes. And then they started
farming too.
Oops, forgot the citations...
Yersinia pestis,
the cause of plague, is a recently emerged clone of Yersinia
pseudotuberculosis
The
Yersiniabactin Transport System Is Critical for the Pathogenesis of Bubonic and
Pneumonic Plague
Hunger
for iron: the alternative siderophore iron scavenging systems in highly
virulent Yersinia
