Replacing non-adjecent variables

Suppose I have an expression of the form $ exp=a\,b\,c\,d\,+\,e\,f\,g\,h$ where all the letters represent real numbers, and I want to replace $ a\,c$ in the first term by $ w\,x$ and $ f\,h$ in the second term by $ y\,z$ , so Mathematica will actually evaluate $ w\,x\,b\,d\,+\,e\,g\,y\,z$ . How do I do that?