I am not sure, most people say coming from us. But could be coming from the source of infection as well. For you the dog? Me I got the dose in this house from water standing on my roof. I have seen the white fibers growing in the sewer and I had a bad flood in the basement. I still see fibers in the air in the basement if it is moist.
The cleaning really helps, DE spray ( 40% water 40% alcohol and 20% dishsoap and as much de as you can get to dissolve in a chapin type sprayer ) It did not harm anything I sprayed and I sprayed it everywhere walls, furniture, floors. Wear a mask. Once it is dry it will not go airborne. It stops them but does not kill them. Some people use air filters ( check fungis posts ). I use menthol and close the room off. Airs out quick with a fan. Vacuuming with hepa helps a lot too.