The novel “The Brains of Earth”, also published as “Nopalgarth”, by Jack Vance was published for the first time in 1966.

Paul Burke’s life changes when he receives an envelope containing a metal disk that floats in the air. When he receives a phone call from the sender, he ends up involved in an interstellar affair with an encounter with an alien named Pttdu Apiptix. L’alieno transports him to the planet Ixax to obtain his help to end a war that devastated his planet for a century.

Pttdu Apiptix explains to Paul Burke that the terrible war ravaged Ixax after the discovery that the inhabitants were infested with psychic parasites they called Nopals and that they also infest humans. To detach the Nopals from someone it’s necessary to use a machine that causes excruciating pain and the treatment must be repeated every month to prevent the parasite from re-attaching. Burke must find a way to subject humans to the same treatment or they will be exterminated.