Scientists Sequence Genome of Ancient Plague Bacterium – NYTimes.com
[Via NYT]
After the Black Death reached London in 1348, some 2,400 people were buried in East Smithfield, near the Tower of London, in a cemetery that had been prepared for the plague’s arrival. From the teeth of four of those victims, researchers have now reconstructed the full DNA of a microbe that within five years felled one- third to one-half of the population of Western Europe.
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Nice article but it fails to mention the most likely reason for the lack of virulence of the present bacteria – humans are genetically different.
It is very likely that those that survived the medieval plague were genetically protected by some factors. Those that were at risk died.
This is what natural selection does. The diversity in genetic backgrounds among the population meant that some people were more likely to die from the plague while others would have protective factors. The plague killed a lot of people but those that lived were protected in very important ways by their genes.
These genes were passe down and still protect us. Until the bacteria changes itself to a form we can not protect against. Then another selective event will happen.
This happens all the time with infectious diseases. Take syphilis. It used to kill people within months. Now it can take years to kill.
The best circumstance for an organism is not to kill its host. Then it often dies itself. So there is also selective pressure on the organism to lessen its virulence and find a balance.
The plague bacterium may have done thins but with so few real changes in the last 700 years, I would expect that direct human selection has been a driving factor in its reduced virulence.
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