I went to our local pet shop and they advised me that it could be a recurring problem as the lice live in the hay/straw used for food and bedding. I asked if there was anything I could do to prevent it, but they said not.
So, I've taken it upon myself to solve the problem!
(sorry if this seems a really obvious solution!)......
Basically when I buy hay/straw now I put the entire bag in our freezer and leave it for about 24 hours. When you take it out again it will be cold, but after a short while it will be edible again. The freezing process kills any lice that may be present in the hay/straw. This has worked really well so far, my guineas haven't had any more lice since.
Just thought I'd share this, and I hope it helps!
