Peeps

Peeps (also Parasite Positive) is a 2005 novel by Scott Westerfeld revolving around a parasite which causes people to become cannibalistic and repelled by that which they once loved. It follows the protagonist, Cal Thompson, as he lives with this parasite and tries to uncover a possible threat to the whole population of the world. The apocalyptic threat to the world that begins in Peeps continues in The Last Days, which features some of the same characters.