My recent rescue, Sonny, had very bad flea and parasite infestations and was on Pancour, Metronidazole, and Drontal. He's had two doses of Frontline, mostly recently two weeks ago. He has become increasingly itchy and scratchy and whiney. I keep combing him with a flea comb and see no live fleas. I just took a picture of some fur I combed that contains black specks--can you guys tell me what these are? Are they flea dander, or some kind of mites? I'm trying to avoid another expensive vet bill (though of course I will take him if the itching doesn't settle down soon).