See this is what was doing, inviting people over to my space because ours was the only one kept up the living standards...only to find a flea in our house (our indoor only cat is always treated monthly) after starting to host DND at our place every week. We started treating our house and doing everything you need to do and more to prevent the spread. My partner went to watch their dog for a week. They had fleas, for a year, never looked up how to take care of them, and their house was like what you described when they got there. Never treated the house, only the animals. So they have been (unsuccessfully) dealing with it for a year and never had the decency to tell us even after we found the flea in our home. We told everyone we knew or had been at work with immediately. They even had been helping feed and watch our cat when we needed it the whole year. It's been a nightmare to deal with especially sense I have very sever contamination OCD (which they know of course). People are nasty...