I just adopted a new boy from a girl that was in desperate need to re-home her rats - I wasn't really ready to get another rattie now, but he really needed help - so, I took him! He is scratching A LOT - ugh - she said he had no parasites and I have looked him over quite thoroughly and cannot see anything - but he keeps scratching. So, what parasites could potentially cross species to my dog and cats - not rat lice as they are species specific - obviously fleas could pass - what about mites?? And would Ivermectin (horse wormer) work for Lice, Mites or Fleas?? Please help!!