Black Death Rat-Flea Transmission Chain

Timeline

1. 1321–1330Central Asian steppe and northern slopes of the Tianshan · Central AsiaIn the early 14th century, mass mortality reports appeared along Central Asian trade routes and around military camps; later scholars regard these as precursors to active plague reservoirs and the expansion of rat-flea populations, preparing conditions for the plague's westward spread overland.
2. 1347–1351Mediterranean ports—Western European cities · Western EuropeThe plague bacterium, transmitted by bites of infected fleas, caused bubonic plague; high rat density in port warehouses and slums accelerated person-to-person spread. Within four years, Europe lost between one-third and one-half of its population, and urban and rural social structures, labor service, and religious life were transformed.
3. 1500–1700Italian and Southeastern European cities · ItalyAfter the Black Death, Europe still experienced periodic plague outbreaks; cities implemented epidemic prevention measures such as quarantine ports, isolation stations, and rodent control. The flea-rat-human transmission chain was only gradually broken after sanitary conditions improved in modern times.