Plague and Rats (Plague and Rye redux).
Entry posted by Pertinax
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Primus Pilus kindly sent me a copy of "Justinian's flea"
http://www.amazon.co.uk/Justinians-Flea-Pl...2722&sr=8-1
Which I intend to review in full shortly.I have however been receiving pms from forum members regarding both the Antonine and Justinian episodes, and I now wish to give a short summary of additional information regarding possible causation.
Of the fascinating transformation of Yersinia psuedotubercolosis into Y.pestis (the actual "plague") I will leave you to discover from the book , save to mention that bacteria are (unknowingly) smart , and they will achieve their mission!
My previous blog entry ""Plague and Rye" (just scroll back a little way) expounds on the plausibility of Ergot of Rye predisposing a population to auto immune deficiency , thence making any aggressive viral incomer more effective in its epidemic effects (or indeed tipping gross morbidity into epidemic status). Ergotism flourishes when grain suffers a cool damp summer, and is compounded by poor storage (lack of ventilation) and processing of infected grain. Remember that Ergot was not even recognised as a parasitic fungus till very late in the history of cereal production.
The vectors that brought the Justinian episode to a head are quite remarkable, but most crucially the enabling factor that lead to a "critical mass" of black rats as the instruments of contagion was cool, damp, summer weather. So ergotism and rat population both thrive in such circumstances, an unhappy coincidence especially as they are also related to the storage of grain in proximity to population centres. Most unhappy indeed because humans are not actually the desired host for the parasite flea, the rat is its most desired target .The flea that hosts Y pestis is Xenopsylla cheopsis, and was so chosen because it is easily blocked by pathogenic bacteria, ie: it fails to digest harvested blood, goes into a biting frenzy and dies.this is of course the desired vector operating most efficiently from the Y pestis point of view, propogating its sisters in the medium of rat blood.
Not any old rat of course but particularly Rattus norvegicus (black) as opposed to Rattus rattus (brown).Now R norvegicus hitched its way from India with ocean traffic delivering pepper, but its favourite food is grain, and it does not care to move far in search of it (being a coastal type) , so a comfortable grain ship moving from Egypt to Byzantium was in essence a mobile home with all mod cons.Now X cheopsis didnt originally care for R norvegicus, it actually jumped ship from the egyptian nilotic rat for reasons unknown (tasted sour perhaps?).The chain of causation grows ever more complex.
The problem for humans is if a very abundant rat population is parasitised by the flea containing the plague bacterian, and it is too efficient in killing its hosts The flea is fooled into thinking it is starving by action of the plague bacteria, (a coagulant in its gut does not allow it to digest harvested blood). the flea is impelled to bite more to seek blood .This is fine if the biting is just done to rats, they are smitten with plague,( they die-that being the apotheosis of the bacterian), but not until the fleas have also breed to maintain a reservoir of the virus.Sadly when rat populations hit demographic peaks, having an abundant supply of grain in a concentrated area (Byzantium say) , fleas can then "jump off" searching for hosts and land on (and bite) humans. This is the only method of contagion , one cannot cough bubonic plague onto another human for example. So a huge die off of infected rats leaves humans grossly susceptible to contagion, if weakened by ergot poisoning the fatality rate exceeds the basic likely plague fatality rates considerably.
The book itself is not just about this episode, though the impact of the Justinian plague on the course of world history is enormous.
Post Scriptum:
The three versions of the plague depend on how it affects a person: Bubonic plague is the most common form and results in flu-like symptoms and the swelling of lymph nodes in the neck, armpit or groin into large, painful cysts called buboes.That is the form that the event in Justinians reign took. Pneumonic plague is the least common but most dangerous form of plague. In this form of pneumonia, plague bacterium gets into the lungs of the victim, causing the coughing up of bloody sputum. Septicaemic plague occurs primarily as a secondary disease, Gage says, when pneumonic or bubonic plague is left untreated and the bacterium gets into the victim
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