A basic guide is that with fungal infections, the hair is pulled out easily with little resistance, and often holds flakes of skin on the bottom of the hair shafts. To my knowledge, lacerations from scratching are less common in fungal cases.
From a chemist, Nizoral can be used. I have heard that Alphosyl can be used but have no personal experience, so can't advise on how good they are. Generally, you'd aim to bathe the piggies in the antifungal shampoo once a week for 2 or 3 weeks.