Symbolism, Imagery, Allegory
The rats don’t simply symbolize the plague. They are symbols of people. They die in the streets, on playgrounds, in businesses…and then people follow suit. Although they seem ominous, they are harmless parallels and portents of the human condition rather than a threat to humanity. When they thrive at the end, that is a positive sign that humans in Oran will too. Still, the reader’s indifference to dead rats is like the universe’s indifference to dead people. Bet you didn’t see that one coming.