However, some cats and dogs cannot control the numbers of mites, and the mite population grows out of control. This inability to control the mite population probably relates to an abnormal immune system, which can have many causes. Some examples are:
1. An inherited weakness
2. Hypothyroidism (low thyroid hormone)
3. Excessive cortisone (steroid) production or use
6. Unknown causes (idiopathic)
When generalized demodicosis occurs in young dogs (< 6 months) it is probably an inherited condition (even though the parents may not have exhibited the disease). In cats and older dogs, it may result from internal diseases affecting the immune system. It is important to perform tests to help find the cause.
Localized demodicosis occurs as one or many small, round, red, scaly occasionally itchy areas of hair loss. This form of the disease usually resolves with topical treatment, but in dogs it can be hereditary and may progress.
Any area of the body may be affected; however, the face, forelegs and feet are the most commonly affected areas in dogs and cats. Cats also tend to be affected on the abdomen.
In dogs, a chronic demodectic pododermatitis affects the paws and may occur with or without the rest of the body being affected. This is an extremely difficult form to treat or cure.
Many times demodicosis is complicated by a secondary skin infection. In these cases, cultures and long-term antibiotics are needed.