Did you actually read post #6? That's the post in which I said of myself, "As a non-expert in medicine", and speaking of germs/viruses/bacteria, etc, "we non-experts can't tell the difference". I added, "I could not begin to refine those fairly crude ideas". I genuinely have no idea what an autoimmune disease is, and did not know what Systemic Lupus Erythematosus was until I googled it.You mentioned germs, virus, bacteria.
I know nothing about how doctors classify 'illnesses' and 'diseases', and admitted this. I have much in common with 95+% of the population in that respect. I wrote as someone who knows something about English, but next to nothing about medical terminology. The main point of what I wrote was this: I am simply making the point that, in BrE at least, the two words are not often interchangeable.
Do you have a problem with that?