How do exterminators prevent themselves from being contaminated by bugs?

Fleas are the easiest thing to transport, I will treat my clothing (legs, shoes with a flea product)...heavy roach infestations, I have been driving down the road before and find one had piggybacked on me, but they are usually easy enough to see and address...bed bugs, I avoid doing bed bug work, so cuts down on chance of transporting them.