You should try tea tree oil. It will take care of whatever it is. It could be lice, but unlikely if you can't see them. Mites usually leaves scabs and pin holes. Fungus is also really easy to get from dirty bedding and them laying in it or laying under the water too much. Tea tree oil is much safer for your pigs. Apply several drops and massage into coat. Let soak several hours then bathe them using twice as much tea tree oil as shampoo (just mix in hand). Clean cage and wash everything. Day 2 massage morning and night into coat. Day 3 massage in coat in morning and bathe again at night. Now wait 1 week and bathe again, 1 more week and bathe again, and finally 1 last time a week later to make sure everything is gone (eggs, fungus, mites, etc). Found at health food stores or online. No toxicity as long as they don't drink it (which they shouldn't be). Says it can irritate the skin of small children, but I have never had the pigs have a problem. However, if irritation develops you can rub primrose oil into their coats to soothe.