Answer :
The answer is a. the fact that Oedipus killed his father and married his mother
The "disease" that Oedipus is referring to is the fact that Oedipus killed his father and married his mother. Oedipus is well aware of his troubles are only his and that he is the only one who can sustain them. This king in disgrace was unable to escape his terrible destiny and has to face the horrible consequences. His power comes to an end.