Rats as Plague Carriers?

By Dalton Fountain

“Rats roaming the sewers, some of them dying, heralding the plague”
Drawing by A.L. Tarter, 194-. Iconographic Collections
Wikimedia Common

The issue of the plague didn’t end in the Middle Ages. Plague was still a threat in 19th- and 20th-century London. People in the 20th century understood that rats and plague were linked, because rats carried fleas which in turn carried Yersinia pestis, the bacteria that causes plague. (Ecology and Transmission).

How did the MOH in London deal with rats?

One of the reports mentions the rats to be the source of the plague and that they must destroy all the rats (Poplar 1910). While in another report from the same year they talk about how they came to recognize that it was not the rats that were carrying the plague but the fleas on them and gives examples to prove it (Stoke Newington 1910). In the reports we can see that they even knew that the fleas carried the bacteria that caused the plague as well as what caused them to get the plague (Acton 1901). Because they recognized the role of rats in spreading the plague, they worked to eradicate rats in mass numbers in attempts to prevent the plague from appearing (Port of London 1912). The medical officers of the period even tried to capture rats for study of the disease and sent letters to mayors asking them to inform him if they found any neighborhoods infested (Poplar 1911).

“A rat stowing away on a ship, carrying the plague further”
. Drawing by A.L. Tarter, 194-. Iconographic Collections
Wikimedia Common

One way that rats were transported in the time period was through ships and port cities like London. In the reports we can see that they exterminated rats whenever they found them on ship out of fear of them bring or spreading the plague (City of London 1919). Towns and ports took great precautions against the rats and the risk of them spreading the plague. One report describes how medical officers would board the ship and take into account the amount of rats and how many were infected, even marking the number of each color rat to try and see if there was a correlation between a certain rats’ fur color and them carrying the plague (City of London 1930).

In order to prevent the rats from spreading the plague they made a new job for people to perform: rat searching. Rat searching was where someone would patrol his “district” and would monitor the rats by the labels on their legs they would place to determine if they were infected (Port of London 1929). Furthermore they found ways to tell if a rat was infected by the plague just by their appearance, such as them being dazed, confused and convulsing (London City Council 1900).

The medical officers of the time also had steps that people should follow to dispose of dead rats if they should find the to prevent the chance of it spreading the plague. The method was to pick them up with preferably tongs so as to have no skin touching it then burning the body one sure way to stop the diseases spread (Hanover Square 1900). In one British medical journal it talks about the safety measures they would take on suspected ships to prevent the rats from escaping. they went as far as to placing guards to watch the ropes the ship used to stay at the dock (Shipborne Rats and Plague).

People did many things to prevent the rats and the fleas from entering the city and possibly spreading plague. The medical officers even captured them to observe and experiment on. For the time period these were incredibly effective measure that they took to prevent the “carrier of the plague” from spreading their disease around England.


  1. Acton 1901
  2. City of London 1919
  3. City of London 1930
  4. Hanover Square 1900
  5. London County Council 1900
  6. Port of London 1912
  7. Port of London 1929
  8. Poplar 1910
  9. Poplar 1911
  10. Stoke Newington 1910

Secondary Sources

  1. CDC, Plague and its Ecology and Transmission
  2. “Shipborne Rats And Plague.” The British Medical Journal 1, no. 2105 (1901): 1100.