Well, I have no experiance here, but I have Zapped my cat with no negetive results. She is not a large cat either and I Zapped her for only 3 minutes instead of 7. I did not do all 3 sessions. Her mites went away within a couple of days, so it must have worked! If I were you, I would try it, though you should do so being careful not to over do it and paying attention to any signs of exhaustion and weird behavor in your pets. Maybe try only 1 minute to start, and see how things are in a couple of day. Rats are probably hardier then kittens, and I don't know if I would zap a kitten unless it was desperate. Colloidal Silver
might be your best bet if Zapping doesn't work out.