He was infected and that seemed to be slowly killing him.

He grunted in pain, trying not to give in to his impulses and not succumb to Las Plagas.

You helped him walk quickly towards Luis' laboratory while he had his hand on his heart. He was in a lot of pain and you knew it.

You felt the blood drain to your feet as after several gasps, his eyes rolled back and he almost fell unconscious to the ground.