The koalas cackled with sadisitc glee. Their genetically engineered, fast-spreading retrovirus, "Herpes Maximus" would soon rid all of Australia of those pesky humans, leaving them Supreme Overlords over their arch enemies: the kangaroos. Of course, "Pouch Fever" would soon take care of those hyperactive bastards too.
BWAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!