what's wrong with the 13th captain the one with the gray hair he cough's up blood and stuff sometime's in episodes?

He suffers from an illness called Tuberculosis.
Here Is a link with what it is:
link

I'm not sure but if I do remember correctly I read somewhere that he has a cancer which makes him cough blood. Though I'm not sure. In manga and in anime they keeps saying illness cause I bet they don't know what cause making him weak and cough blood suddenly.