Originally Posted by lionwajih
As far as as I remember at one stage Black Zetsu said, "He Poisoned Itachi".
Nothing was ever said that Itachi was poisoned. Itachi was suffering from an unknown, and fatal, disease. Zetsu pointed out that Itachi seemed out of it (that could be due to Itachi holding back, too) and he was coughing up blood. Besides, who would poison him? Sasuke seems too proud (or insane) to use such tactics.