If it's not the puppets struggling futilely against their strings, it's the parasites eating away at their minds before they can find them to cut them down.

[ He seems oddly gentle when he says that, surprisingly. Seems he picked up on the fact Akira has... suffered somehow. He's not sure how, but he has. ]

And it wants to spread itself. A plague of the mind.

[ You don't look like one, he doesn't say. ]

It would seem to me you have your own personal parasites, Mister Kurusu, that are in need of cleansing.

[ ... In other words, you're suffering from emotional pain and you need help to carry that burden, is what he's getting at. ]