Don't let the bed bugs bite!

We have several rental properties. A few weeks ago we got a call that one of the tenants is having a bed bug infestation. Apparently, this is our responsibility, as the landlords, to have this eradicated. So, we spent several hundred dollars (of our own money) to have them exterminated with a special heat treatment that ensures they kill them all. After being in this business for several years, we've found that it's better to go ahead and spend the extra money to get the job done right the first time, instead of going the cheap way, and having the problem come back. You always end up spending more in the long run when you go the cheap way. I am really concerned about this bed bug epidemic going on. I know they say that it's not an issue of clean vs dirty. That even the fanciest of homes, hotels and stores can have bed bugs. I'm really concerned about it being a recurring problem though, that we have to keep paying for, because our tenants aren't taking the proper precautions. They say that you get bed bugs from a store or a suitcase or a hotel, or something like that. Bed bugs are brought in, by people, from the outside. I'm just wondering where this stops. What if a family in one of our homes were to, say, pick up lice from a kid at school? Now there are bugs in a home of ours. Do we have to pay to get rid of the lice in the family's hair? What if those lice spread to the carpet? Are they now on the home and it's our responsibility to exterminate? What if a tenant brings in a dog with fleas, and those fleas get in the tenants beds? Is it now our responsibility? Where does it stop?