The scourge of Y. pestis re-emerges and persists from 1361 to 1879
The plagues of Europe between the years of 1361 and 1815 are blamed for the deaths of nearly one third of Europe's population. During this 500-year period, plague reappeared every 20–30 years across Europe but in a spatially non-contiguous manner. The plague of 1361 was as lethal as the 1347–1353 primary wave of the medieval Black Death (mBD). Records of mortality in the primary wave of the mBD indicate large cities, ports, and capitals struggled with the plague longer than smaller cities and towns. Bubonic plague, historically accepted as the cause for the epidemic outbreaks of medieval Europe, is spread via a rat flea as a vector. However, analysis of historical records suggests that a rat-flea-human method of transmission is unlikely for the plagues of medieval Europe. In Kazakhstan, plague persists and spreads across the landscape once gerbils reach a gerbil-density threshold, and occupied gerbil burrows form local clusters.