The Black Death: Do Fleas Really Deserve All the Blame?

The Black Death was one of the most devastating events in history.   Originating from central Asia, it is believed to have traveled along the Silk Road until it reached the Crimea around the mid-1340’s.  From there it spread to become a pandemic in the truest sense of the word.  The Black Death was responsible for the deaths of an estimated 30-60% of the European population, and as many as 100 million deaths worldwide.   You all probably know this much already.  You also probably know that this was vectored via the Oriental rat flea (Xenopsylla cheopis) living on black rats that made their way on merchant ships in the Mediterranean initially and then ventured north.  The Oriental rat flea is a nasty bugger, vectoring not just the plague (Yersinia pestis) but also Rickettsia typhi, and tapeworms.  But what if we can scratch one of those off that list?

Oriental Rat Flea

Skeletons unearthed a year ago during a work on a new rail line in London are shedding new light on some of our well established ideas regarding our not-too-distant past.  The bones were believed to be from a cemetery of plague victims.  Molars were removed from the skeletons and DNA then extracted from the teeth.  The plague bacterium was found in several of the teeth, indicating these individuals were exposed to and most likely died from the Black Death.  These results are not unexpected, of course so researchers continued to “dig”.  Archaeologists, geologists, historians, physicists, and microbiologists worked to better understand the circumstances surrounding these individuals lives and deaths.

They were generally poor people showing clear signs of malnutrition, and a history of hard labor.  One may have even been a vegetarian later in their life, possibly indicating a shift to monastic life at some point.  Not completely surprising considering the land was at one time part of a monastery.  These plague victims didn’t come from the same time period either.  With radiocarbon dating indicated the graveyard was used multiple times between the earliest outbreaks (1348-1350) and later ones in 1361 and the early 15th century.  Archaeologists are planning on more digs as they estimate the total number of bodies may number anywhere in the “low thousands”.

Black death researchers extracted plague DNA from 14th century skulls found in east London. Photograph: Philip Toscano/PA

But that’s not the whole story, not by a long shot.  I may be an history buff but I’m also a buggy person right?  So why would I be blogging about this if there were not some new interesting entomological tidbits to be shared?  Because I’m bored, yeah….fascinated with dead things, yeah…but there is buggy stuff to share!  Traditionally the belief has been that the Black Death was spread via the Oriental rat flea, as stated earlier.  But evidence derived from those teeth suggest that this may not be the case; or at least not always the case.

When researchers compared the genome from the molar-derived bacterium with that of more recent plague victims they found the genome largely unchanged.  The recent outbreaks of the plague such as in Madagascar last year saw the majority of deaths from a pneumonic or pulmonary plague.  This new information suggests that the transmission of the plague was likely not just via the rat flea but also likely the pneumonic strain.  This is a more virulent strain of the bubonic plague.  Exposure to the plague from the rat-borne fleas is treated with antibiotics and has a higher survival rate than its cousin.  The pneumonic form, acquired via inhalation and human-human contact, is very highly fatal with death typically resulting within 24 hours of exposure if not treated.  The 60 deaths attributed to the pneumonic plague (84 deaths in total) were believed to be spread in part because of increasing political turmoil in the area resulting in poor hygiene and a decline in living conditions.

This mirrors much of what is believed to have happened during the Black Death.  Political and social instability, significant decreases in living conditions and healthcare availability created a perfect storm of underlying problems.  Perhaps the rat flea gets a bit of a reprieve.  Initial introduction via the rats is likely to have occurred with the more virulent strain of pneumonic plague taking over and doing the most damage.

Research continues and I look forward to hearing about it.

 

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