32. Weather Fluctuations and the Plague
Fourteenth-century weather fluctuations played a key role in the Black Death’s recurrences. The plague bacterium, Yersinia pestis, thrives on fleas that are usually hosted by ground rodents such as marmots – which don’t mingle with humans. However, bouts of bad weather in the 1300s struck those rodents’ habitats and decimated their populations. So their plague-infected fleas fled to alternate hosts such as rats – which do thrive amidst human populations.
A cycle developed, driven by weather fluctuations. Bad weather kills off the usual rodents – which don’t live amongst humans – that host the fleas that host Yersinia pestis. The fleas flee to rodents like rats that live among humans. A Black Death outbreak ensues. While killing humans, the infected fleas also wipe out their rat hosts, extinguishing the plague. Ten or fifteen years later, bad weather again decimates the usual rodents that typically host the plague-infected fleas. The fleas flee to rats, whose populations by then have recovered. The rats reintroduce the flea plagues to humans, and another Black Death outbreak occurs, lasting until the rats die off.
