This thread is what I wanted to ask about. I had noticed more shedding than normal on the lower back of one of my piggies, above her grease gland, with quite heavy dandruff. I took them both to the vet and he combed some of the dandruff out and looked at it under the microscope. he said it was eggs of
Cheyletiella parasitivorax
--- also known as "Walking Dandruff" see
Guinea Lynx :: Fur Mites. Anyway, he gave ivomec by injection, (he wouldn't do it any other way, but he's very knowledgable so I trust his opinion) to be repeated 2 weeks later, with the cage being disinfected in 7 days' time. He reckoned that they came in on the new batch of hay that we just started, which I am so pissed about since it's a 50lb box of Oxbow timothy. I can't risk assuming it was the last of the old box that was to blame, sine if I keep using the new stuff, even discarding the top few inches, there's the risk of further problems. At the same time the new bag I bought might also have mites, just through bad luck. It's impossible to be sure what caused the problem, but the new hay, which they've had for a few days seems probable. He also gave me shampoo to lift the dandruff off the skin, 50.00 x Seleen, which is applied to dampened fur on their back, left for 5-10mins and then rinsed off.
GL recommends ivermectin for these kind of mites and mange mites, so I wouldn't necessarily assume that the gel your vet used cured the problem. Do you know what the gel was?