@Cary93 Unlike bedbugs, which are visible to the naked eye, it's virtually impossible to be certain that your scabies infestation originated in your Airbnb and not another point of contact. However, on the plus side, the mites are not as difficult to get rid of. The first person that you should inform is your host; even if they deny their property being the source of your scabies, they should have a vested interest in making sure the surfaces are fully disinfected and the bedding is properly washed and quarantined to prevent the scabies being passed on to the next guests.
I don't think Airbnb admin is going to be interested in the fact that you have an uncomfortable but highly treatable parasite. If you want to alert prospective guests of this listing of your plight, you have the opportunity to do so in your review. I don't necessarily think it's a good idea to do this, because it's pure speculation on your part that the scabies came from the Airbnb and not from another source. But if the property was unclean or poorly kept in general, this would certainly be relevant to a review.