Final answer:
The plague primarily spread within families through fleas that infested rats and transmitted the disease when biting humans.
Step-by-step explanation:
The plague, also known as the Black Death, primarily spread to the rest of the family through fleas that infested rats. Rats were common in households, and these fleas would bite the rats and become infected with the bacteria that caused the plague. When the fleas bit humans, they would transmit the disease to them. Close contact with infected individuals or sharing living spaces with them would further facilitate the spread of the plague within families.
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