Who carried the rat plague? - briefly
Rats aboard medieval trade vessels transported the disease across continents, while their fleas served as the actual vectors of Yersinia pestis. This combination enabled rapid spread of the plague throughout Europe.
Who carried the rat plague? - in detail
The rat plague spread primarily through three interconnected agents.
- Fleas: The oriental rat flea (Xenopsylla cheopis) acted as the biological vector, ingesting Yersinia pestis from infected rodents and transmitting it to new hosts during blood meals.
- Rodents: Black rats (Rattus rattus) and, later, brown rats (Rattus norvegicus) served as reservoirs, maintaining the bacterium in their populations and facilitating its geographic expansion.
- Human transport: Merchant vessels, caravans, and overland trade routes moved infested cargo and animals across continents, allowing the disease to reach distant urban centers.
During the 14th‑century pandemic, ships departing from the Black Sea region carried infected rats in their holds. Port cities such as Kaffa received these vessels, where dense rat populations and unsanitary conditions enabled rapid flea proliferation. Subsequent inland movement relied on caravans traveling the Silk Road, where rodents hid in grain sacks and traders unwittingly spread the pathogen to inland markets.
In later outbreaks, urban sanitation failures intensified the problem. Overcrowded housing, inadequate waste disposal, and close proximity between humans and rodent colonies increased human‑flea contact. Public health measures that targeted rodent control, flea eradication, and quarantine of transport vessels proved effective in interrupting the transmission chain.
Overall, the combination of ectoparasitic insects, rodent hosts, and human-mediated transport constituted the primary mechanism by which the rat plague was disseminated across regions.