Thanks so much for the info! I will do some reading. I always use ivermectin topically. I went back to the pet shop today and talked with the owner. She had a lot of rats this time including some more tiny babies.  She said that the rats come from different sources and you could easily see the difference between them. Fat and healthy appropriate aged ones versus thin, scraggly tiny ones. She said that a young boy raises some and sells them to her and that his mother works for a vet. I am assuming she meant the tiny ones. I told her she needs to speak to him and to contact a vet to get rid of the lice. When she asked me to show her the lice she put a sweet healthy one in my hands. While I was checking him he was bruxing and started cleaning me, then he peed in my hand. He never made it back in with the rest of the ratties. He came home with me..........Oh well.   Nancy