Nasus becomes very strong from level 7 with Sheen, so either shut down his early game with jungle ganks or pick specific counter champions like Darius.
He is not an infinite scaler; his power diminishes when enemy ADCs acquire 3-4 items or in teamfights past 35 minutes.
While his W can be frustrating, if you can't contain him, focus on empowering other lanes or matching his split push with Hullbreaker.