Orochimaru is afraid of Itachi. I forget the chapter, but one of the first times that we see Orochimaru and Kabuto after the failed assault on Konoha, Kabuto mentions to him that even if they can't get Sasuke, there is another who possesses the Sharingan.

Orochimaru responds...and this is unmistakable...'No, he is stronger than I am.'

Definition Horse's Mouth.