Lots and lots, but also we are immune to a lot of them, either naturally or from vaccination. Also, most of us have good sanitation.
If your relation caught worms from eating a shop sandwich, it most likely was from what was in the sandwich or because the person did not wash their hands after touching their bum. Either way, I believe most people wash their hands more frequently than most dogs do. You may disagree.
Dogs and cats don't live on farms.
No I do agree. As I said earlier we were told to wash our hands and do not put them in our mouths and you are correct about the sandwich (human to human).
Regards people. Nearly all the diseases we catch are from other people and not from animals. In fact very few are from animals.
Lots of dogs and cats live on farms. They are an important part of a farm.