Final answer:
The plague spread through infected rats and fleas along trade routes, as well as through unsafe food practices.
Step-by-step explanation:
The plague spread through a combination of factors. One of the main ways it spread was through **infected rats** that traveled along trade routes, such as the Silk Road, from Europe to Asia. These rats were bitten by **fleas**, which then transmitted the plague to humans. Another factor was the **unsafe methods** of harvesting and storing food, which allowed for the breeding of rats and fleas. Lastly, the movement of infected **fruits and vegetables** along trade routes also contributed to the spread of the plague.
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