took my pug back to the vet for check up on what we thought was a skin allergy and it turns out he has demadex mange i am very upset and worried about him has anyone had any experance of this its not all over him just on his legs and chest he is haveing aludex baths at the vets weekly and then skin scrapes after the fourth bath

Don't worry, it is not nice to treat but it will clear up and it does not worry the dog too much. TBH it is better to have that than some sort of skin disorder that can't be diagnosed and therefore the treatment is very hit and miss. Only real problem is you should not breed from a dog that has had it as it is considered to be a sign of a poor immune system and can/may recur at stages throughout his live at times of stress such as if he should have to have an operation.

Most dogs are born with demodex mites.  These only cause issues if they proliferate too much.  Occasionally slight symptoms appear (usually hair loss around the eyes and small hairless lesions) when the immature dog is under stress like changing homes, a first season perhaps, the symptoms resolve without treatment as the immune system matures and no further problems arise.

If it is more generalised the dogs immune system may be faulty as opposed to immature, and these should not be bred from (in case the tendency is inherited), and the breeder should be informed so the same parents are not mated to gather or tow partners of similar breeding.