Is there a word for thinking of something as a disease?
Solution 1:
There is a word "pathologise". If, for example, I try to explain someone's criminal behaviour in terms of the person's psychological state, and their deep-seated emotional needs, then I am "pathologising" behaviour that the authorities may look upon in a legal or moral way.
Americans would presumably spell it with a Z.
Is that what you are looking for?
Solution 2:
James’s influence is contagious:
(of an emotion, feeling, or attitude) likely to spread to and affect others.
(Lexico)