We don't treat our rabbits for fleas in the winter because we don't [take them out](https://pets.stackexchange.com/questions/925/how-do-i-get-rid-of-fleas-on-my-rabbit/1016#1016) in the winter.  Sometimes in the winter we will take them to the pet store or other locations where cats and dogs are also present.  

What risk, if any, is there of rabbits having a problem with fleas from a cat or dog?