How did the disease spread to humans?
Study the flow chart above on how the Black Plague infected humans:
1 - Rat infestations
In urban areas where rodents tend to live in large numbers, the plague bacteria passes between rats and their fleas.
2 - Bacterial growth
The plague bacteria multiply in the flea’s stomach and cause a blockage.
3 - Bad blood
After 10–14 days the infected rat colony dies, and the fleas turn on humans in search of fresh food
4 - Flea bite
The hungry flea bites a human and regurgitates the bacteria in its stomach during feeding
5 - Infected
The plague enters the human’s bloodstream, and symptoms manifest within three to seven days.