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Offline krool1969

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Is yersinia pestis weaker?
« on: 24/10/2011 23:34:21 »
The Naked Scientists recently ran a story about Yersinia pestis, the Bactria that caused the Black Death of the Middle Ages. In wondering why Yersinia pestis is not as deadly today as it was then they speculated that the bacteria is weaker.

It seems much more likely to me that humans are stronger (on average).

Durring the Black Death more than half the population in Europe died. This means that everyone, Every single person alive at the time was exposed to the disease. So every person who who was vulnerable to it died, while every person who had resistance survived. After the Black Death finally burned itself out all the survivors possessed resistance. These survivors passed their resistance down to us.

It's basic natural selection.


 

Offline Don_1

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Is yersinia pestis weaker?
« Reply #1 on: 25/10/2011 11:34:36 »
Take a look at this recent article from the BBC http://www.bbc.co.uk/news/health-15278366
 

Offline krool1969

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Is yersinia pestis weaker?
« Reply #2 on: 25/10/2011 19:50:15 »
interesting but it says nothing about why the Black Death is less virulent today. I think there are several reasons but hygiene and gentic resistance are the most important. Everyone alive today are descended from the survivors of the Black Death thus everyone today is at least somewhat resistant to the disease.
 

Offline CliffordK

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Is yersinia pestis weaker?
« Reply #3 on: 25/10/2011 20:20:34 »
Take a look at this recent article from the BBC http://www.bbc.co.uk/news/health-15278366
It does indicate that Yersinia Pestis has had some genetic drift over the centuries. 

The question is how the plague reached Europe.  Where did it come from?  Did it make a jump from an animal species to humans, or was it endemic to a small remote human population, only released by the increased trade of the Renaissance?  Anyway, it is likely that it was a novel bacterium to a large number of people during the Renaissance.  The article is a bit unclear, but other earlier plagues may have been a different bacterium.

I'm going to go with a combination of less virulent bacterium, better treatment for the infections, better hygiene, and some genetic immunity.  Buboes, for example, are rare in Western Civilization.
 

Offline chris

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Is yersinia pestis weaker?
« Reply #4 on: 25/10/2011 20:28:27 »
Just to correct a minor inaccuracy posted above, we didn't speculate that the bacterium was weaker today than it had been historically. In fact what we said is that one theory to account for the apparent enhanced historical virulence compared with strains of Y. pestis circulating today is that the bug behind the Black Death may have been subtley different in some way. This theory was actually dismissed by the new findings that we reported on, which show that the genome of the Black Death strain is nearly identical to that found today. For this reason, scientists speculate that perhaps a co-infection, a genetic vulnerability, living conditions, climate or a disease factor such as the flea vectors that spread it were behind the virulence of the pandemic episode that struck 14th Century England.
 

Offline krool1969

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Is yersinia pestis weaker?
« Reply #5 on: 27/10/2011 02:47:13 »
Take a look at this recent article from the BBC http://www.bbc.co.uk/news/health-15278366
It does indicate that Yersinia Pestis has had some genetic drift over the centuries. 

The question is how the plague reached Europe.  Where did it come from?  Did it make a jump from an animal species to humans, or was it endemic to a small remote human population, only released by the increased trade of the Renaissance?  Anyway, it is likely that it was a novel bacterium to a large number of people during the Renaissance.  The article is a bit unclear, but other earlier plagues may have been a different bacterium.

I'm going to go with a combination of less virulent bacterium, better treatment for the infections, better hygiene, and some genetic immunity.  Buboes, for example, are rare in Western Civilization.

I think it's well known that the disease came from Asia via trade through the Mediterainan. One vector of spread was warfare which helped it spread faster.
 

Offline cheryl j

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Is yersinia pestis weaker?
« Reply #6 on: 28/10/2011 08:22:39 »
Survival may have also been affected by how you caught it, whether directly from the flea that transmitted it, or from another person. A person with oozing boboes or the respiratory form of plague might deliver a much higher dose of it to the next person than a flea would.

Some zoonotic bacteria can actually become more virulent after being passed a few times through a different animal host than the one it normally infects, but I dont know if this is true of Y. pestis.
 

Offline krool1969

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Is yersinia pestis weaker?
« Reply #7 on: 17/11/2011 05:40:07 »
Survival may have also been affected by how you caught it, whether directly from the flea that transmitted it, or from another person. A person with oozing boboes or the respiratory form of plague might deliver a much higher dose of it to the next person than a flea would.

Some zoonotic bacteria can actually become more virulent after being passed a few times through a different animal host than the one it normally infects, but I dont know if this is true of Y. pestis.

This would support my idea that ALL the survivors of the plague were highly resistant to the bacteria. The most likely meathod of contracting the disease would be from caring for a loved one who was suffering from it. Washing wasn't highly practiced so most people probably went directly from caring for the sick to preparing food. If you do that then it's very unlikely you're going to get it at all.
 

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Is yersinia pestis weaker?
« Reply #7 on: 17/11/2011 05:40:07 »

 

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