Only thing I can contribute is that one of my sister's cats had flea anemia and had to be put down. She had 5 or 6 cats at the time, and could flea treat all but 1. I don't know how often she flea-bombed, but I doubt it was very often. She called me one day because she was worried about him, the way he was crying, and I heard him in the background. My first thought was, because he's male and she feeds dry (supposedly most of the cats "don't like wet"), he had a urinary blockage, and I told her to get him to the vet ASAP, which she did.
They tried to treat him, but overnight he began having seizures. They called her and she told them to let him go.
But I don't know what other signs/symptoms he might have had, or how much (if any) scratching my sister saw from him or any of the other kitties.
I'd tell her to do the paper towel test with all the others to see if anything is spreading around.
Good idea, and couldn't hurt. If nothing else, it confirms or rules out any fleas on the animal.