To pervade means to be present throughout, to exist in every part of. If you have too many cats, the horrible smell of cat pee will pervade your house.
You can use pervade both for external things like smells and sickness, and for more internal things like feelings. For instance, you can say that a feeling of doom pervaded the army as they caught sight of the opposition’s superior forces. Despite efforts to prevent bullying, peer pressure and clique mentalities pervade the school environment.