Hi!
A full course of mites treatment consists of 3-4 rounds of good quality ivermectin at the product specific interval. The first couple of rounds should take care of the itchiness. The third and fourth round of stragglers. Please contact your vet as to what product and he has been using and how soon you should treat for the repeat. You can get xeno online if your vet OK with that.
You do not need to get rid of the fleece. A good deep clean and a fleece wash at 60 C should do the trick. Most piggies have got mange mite eggs burrowed in their skin, which are usually kept under control by a fully working immune system. The ivermectin can deal with any emerging mites, but cannot kill off the eggs although regular low-dosed preventative treatment can contribute to the mites developing resistance to ivermectin. It is therefore generally better to hit the mites with a good product if and whenever you have an acute outbreak.
Hay or fur mites where the small visible egg cases are attached to the bum hairs come with hay. If you have a hay mite infestation, you need to get rid of the hay, first and foremost, but otherwise just do a good deep clean and high temperature wash. Some of the new strains that obviously come with imported pet shop hay in the last couple of years seem to be much more resistant to treatment than those that usually come with untreated cheap farmers hay in autumn. Hay mites are the least bothersome for the guinea pigs while mange mites are the worst.
