Final answer:
The plague was primarily spread through fleas that infested rats, which then bit humans. Direct contact with infected individuals or unsanitary living conditions also contributed to the spread of the plague.
Step-by-step explanation:
The plague, also known as the Black Death, was spread primarily through fleas that infested rats. When an infected rat died, the fleas would look for new hosts, including humans, biting them and transmitting the bacteria responsible for the plague. The bacteria, Yersinia pestis, could also be transmitted through direct contact with bodily fluids or tissues of infected individuals. Additionally, overcrowded and unsanitary living conditions in cities facilitated the spread of the disease.
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