
Demodex is a naturally occuring mite that lives on the skin pretty much like the mites we all have living in our eyelashes. In a normally healthy dog it would cause no problems. If the immune system becomes compromised in some way then the mites proliferate and can start to cause a problem. The immune system of a puppy can quickly become compromised by too early vaccination, too vigorous chemical worming and flea treatment, antibiotic treatment, corticosteroid treatment, poor diet along with stress. It may just be one factor or it could be a combination of factors that stress the immune system to the point where it can't handle the demodex mite and starts up with a skin condition.
Homeopathic Sulphur and Psorinum can make the body hostile to mites and could probably help once you have the condition under control but you could always ask your own vet for a referral to a Homeopathic Vet and try to solve the problem naturally..??
Many many skin conditions arise within 3 months of a vaccination event and although I suppose its difficult to prove the link between the vaccine and the skin condition, its just a bit too much of a coincidence for my liking (in fact i find the statistics for so many health problems arising within 3 months of a vaccination really alarming, and would rather seek a natural alternative if there is one)