After killing his family he went to a bar, got drunk, a bunch of gorgeous women saw this new hotness, banged 'em all and somehow got an STD.I remember watching it on the anime, but i never really remember what his illness was.
Was it elaborated? or it a mystery?
Honestly, I just think it was the overuse of the MS powers. The other MS wielders didn't get it either because of a quick transplant(Madara and Sasuke), having aided by Senju DNA(Obito) or awakening it recently and losing it(Kakashi).
Madara was coughing up blood in the anime when he went blind. But tht was itachis illusion