@Piggies&buns,
@Wiebke or someone else could tell you what to do action wise. Until then you could deep clean their cage with F10 or any other veterinarian grade cleaning solution. Also replace all hay. Wash your hands especially after holding a piggy with parasites. Fungal infections could cause dandruff in any guinea pig. Separating is not necessary if all guineas in a herd have been exposed and are all infected together and it would stress them even more. What happens if you tug on hair? When you brush the hair does none of the white spots come out? How much are they scratching? Is there a clear v shape?
Guinea Lynx :: Lice
Lice
New piggy problems: URI - ringworm - skin parasites
Hi
Static lice fix their tiny eggs to the hairs; the egg cases don't come out by brushing and the hairs don't fall out like in a fungal skin infection (ringworm fungus sits on their hair roots). There is no distinct pattern to a hay mites outbreak; it often starts in the underlayers of the hairs at the bum end because hay mites live off skin debris for which the area around the bum is prime estate, so to say but a more severe outbreak can spread all over the body and cause irregular bald patches from scratching.
What you can do mechanically - in addition to ivermectin/selamectin - is to cut off all the hairs that have egg cases on them (feel for the tiny beads if necessary). This means that the next generation of hay mites will be a lot smaller and there is also not as much space to fix eggs on. The hairs will grow back normally within a few weeks.
The problem with hay mites (we no longer use the expression 'static lice' anymore since it is both incorrect and outdated) is that they are the least harmful of the cavy specific skin parasites since they do not burrow their eggs into an increasingly inflamed skin (unlike mange mites) and that they do not suck blood (unlike cavy lice, which are the only visible skin parasite that guinea pigs have).
But because they do pick up the medical products indirectly, they can sometimes be hard to eradicate; especially the strains that come with industrial scale harvesting methods where the soil is a lot more churned up than in traditional small scale harvesting methods. If you struggle medically, then a combined treatment of medical treatment and medicated baths may do the trick but you need to plan that carefully because you always have to wait 48 hours in between any skin treatments to allow the previous one to be fully absorbed. Also be aware that most pet shop products are too low dosed to do the trick. You'll need vet strength ivermectin/selamectin and you have to be very careful not to overdose. This is why we strongly recommend to see a vet, as well as for an identification of which parasite you are actually dealing with.
Ringworm, which is a fungal skin infection, is something very different but in the initial stages and especially if the bald or bloody patches are not textbook (which is actually not all that rare), it is very easy to misdiagnose - with sometimes sadly fatal consequences. You should not get any bloody patches with hay mites, though.
