Can fleas and ticks affect other pets or people?

Yes, because they're all going to go to whatever is the most available food source. If you bring in a stray cat with fleas and you have other pets that you haven't had on flea prevention, it won't take more than about three days before everybody is infested. They can also affect people, but humans don't have a lot of hair, so we don't have a whole lot of ability for them to create skyscrapers on us.