My Dog Is Itchy After A Visit To A Relative's

My dog is itchy after a visit to a relative's where they suddenly brought up fleas. He's never had them and I can't find any. However, there are blood flakes in his fur on either side of his anus. He started scooting after I treated his underside with apple cider vinegar. I've seen pics of flea dirt and this doesn't look the same. I've also been applying coconut oil with a couple drops of oil of oregano to the areas where he's itchy. I have a photo of the blood flakes which I've only found on his hind quarters.