How did rat-proofing ships and port facilities help control plague?

Rat-proofing ships and port facilities was a critical strategy in controlling the spread of plague because it severed the primary transmission link between rodents and humans.

Historically, plague was spread globally via maritime trade routes, as domestic rats traveled on seagoing vessels and proliferated in crowded port cities. Researchers eventually discovered that the disease is transmitted by fleas that live on these rodents. When an epizootic outbreak kills the rat population, these infected fleas seek new hosts, often biting humans and transmitting the Yersinia pestis bacterium.12

By implementing massive rat-proofing measures in maritime vessels and port facilities, authorities effectively limited the movement of these rodent hosts and their associated fleas. This intervention, combined with the use of insecticides, successfully disrupted the rodent-flea-human cycle. These efforts were instrumental in ending the third plague pandemic and ensuring that plague is no longer considered an epidemic disease of port cities.1