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Student Question: The Plague

Dan Lyndon

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We recently held a gifted and talented day with an outside speaker / facilitator and the topic that we were looking at was about genetic disease and DNA. However we somehow got onto discussing diseases such as the plague and one of the students asked this question:

Is it true that the bubonic plague might not have been spread by fleas after all?

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Susan Scott and Christopher Duncan have been arguing for several years that the Black Death of 1347 was really a strain of Ebola or Marburg viruses (Biology of Plagues: Evidence from Historical Populations - 2001 and Return of the Black Death – 2004). This claim was publicized in a recent edition of BBC Timewatch (October, 2004). As one reviewer pointed out, the message of the programme was that “it could be merely lying in wait, ready to strike again”. This was an example of sensationalist tabloid television that is so common on BBC in recent times.

The programme makers correctly explained how people caught the bubonic plague. The pestis bacterium establishes itself in the flea's stomach where it multiplies rapidly until the organ is completely filled. The flea's stomach eventually becomes blocked. The infected fleas now becomes ravenously hungry because no blood can enter its stomach. To obtain more food it has to regurgitate some of the blood in its stomach. The plague bacilli now enters the rat. The rat will eventually die of the plague. When this happens the flea has to find a new host. It will try to find a rat but if none are available it will find another animal. Failing that, it will bite the nearest human being. In virtually every case the cause of infection is from animal to man. It is fairly rare for bubonic plague to be spread from person to person.

Therefore, Timewatch argued, you would always find dead rats during the outbreak of the Black Death. They quoted sources that suggested that rats were not always present. This can be explained. Most experts in this field would have been willing to explain why these rats were not found during certain periods of this disease. However, the filmmakers dishonestly did not call on these experts and relied on those who supported the Ebola virus theory.

What happened is that during the summer of 1347 the world was ravaged by the bubonic plague. This was indeed passed by rat fleas. However, during the winter, the bubonic plague developed into pneumonic plague. This is when the pestis bacterium becomes localised in a person's lungs. The victim of pneumonic plague will begin to cough up blood. The plague will now spread directly from human to human by 'droplet' infection. This is the deadliest bacterial disease known to humankind and virtually everyone who catches the disease will be dead in four days. Most people died during the Black Death of pneumonic plague, not bubonic plague. Pneumonic plague has nothing to do with rats and that is why they were not in evidence during this outbreak.

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  • 5 years later...

One irony of the Great Plague of 1666 - which itself is said by some sources and documentaries to have been a mutated version of the 'lying low' 1348 Black Death pandemic centuries before- was that to prevent the worsening of the illness, was London Mayor's desperate decision to order a cull of the "culprits"- cats and dogs.

As we know today, it was the flea-infected rats that were the cause, and that the canine/feline cull was exactly the wrong decision, as those animals were likely to have lessened the spreading of the infected rats. As it was, the rats were allowed to spread to other areas unchecked.

Edited by John Wilson
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