The Life Cycle of Plague

Plague is our first real zoonotic disease and vector born. A flea takes a blood meal from an infected, let's call it a rat because those are really common. And the amount of bacteria that is in the rat's blood directly correlates with the percentage of fleas that get infected. Within three to nine days after taking that infected blood meal, the bacteria have multiplied so much that they entirely block the esophagus of the flea.