tl;dr "Theoretically, yes [you can catch diseases from the toilet seat], but the risk is vanishingly low," says Jill Roberts, a professor of public health and microbiology. Also covering seat in toilet paper doesn't really work against germs.

I carry a small bottle of 70% isopropyl alcohol so I can wipe down the toilet seat. Feels cleaner than just using a paper seat cover that shifts around.