I will just copy and paste what I found on a Tool FAQ. I don't think they've done "Ticks & Leeches" before but the FAQ is fairly old.
Why haven't they played "Ticks & Leeches" live yet?
"All of the songs with lyrics from "Lateralus" have made it onto setlists so far except for this one. Maynard recorded vocals for this song after all the others, and threw his voice out completely for a few days as a result of the screaming. In Oor Magazine (May 2001), he says "the band can hassle me all they want about Ticks & Leeches, I won't do it live. Three weeks it cost me. I couldn't sing a high note."
Either way all correct points. And yes I will edit the "encore" part out b/c yes that is correct they don't do encores.