Transmission of the mites is by direct contact only. That is, the mother and puppy must be physically touching, as the parasite cannot survive off of the animal. This is important because it means the kennel or bedding area does not become contaminated and therefore the environment need not be treated. Lesions, if present, usually appear first around the puppy's head, as this is the area most in contact with the mother. Virtually every mother carries and transfers mites to her puppies.
Most puppies are immune to the mite's effects and display no clinical signs or lesions.
A few are not immune and it is these that develop into full-blown cases of mange. Most lesions in either form develop after four months of age. The lesions and signs of demodectic mange usually involve hair loss, crusty, red skin and at times a greasy or moist appearance. The mites prefer to live in the hair follicles, so in most cases hair loss is the first noted sign. Usually hair loss begins around the muzzle, eyes and other areas on the head.