What is demodectic mange?
Mange is a parasitic skin disease caused by microscopic mites. Two different mange mites cause this skin disease in dogs. One lives just under the surface of the skin (sarcoptic mange), while the other resides in the hair follicles (demodectic mange). Although the mites have similarities, there are also important differences. It is important not to confuse the two types of mange because they have different causes, treatments, and prognoses.
What causes demodectic mange?
Demodectic mange is caused by a parasitic mite (Demodex canis or Demodex injal) that lives in the hair follicles of dogs. Under the microscope, this mite is shaped like a cigar with eight legs. Demodectic mange, sometimes just called "demodex" or “red mange,” is the most common type of mange in dogs.
All dogs (and many humans) have a few of these mites on their skin. If the body's immune system is functioning properly, these mites cause no harm. Demodectic mange usually occurs when a dog has an immature immune system, allowing the number of skin mites to increase rapidly. This disease occurs primarily in dogs less than 12 to 18 months of age. As the dog matures, its immune system also matures.
Adult dogs with demodectic mange usually have weakened immune systems. It may occur in older dogs because the immune system declines with age. Dogs with a weakened immune system due to illness, malnutrition, or certain medications are also susceptible.
Is demodectic mange contagious?
No, demodectic mange is not contagious to other animals or humans. Demodex mites are transmitted from a mother dog to her puppies during the first few days of life and are found on the skin of virtually all dogs. Because these mites are a normal inhabitant of canine skin, exposure to a dog with demodectic mange is not considered dangerous for a healthy dog. Demodectic mange develops when a dog’s immune system cannot keep the mite population under control, allowing the mites to multiply excessively.
Why doesn't the immune system mature correctly in some dogs?
The development of the immune system is influenced by genetics. As a result, an affected dog often has littermates that are also affected. Owners of littermates should watch for signs of mange in their puppies. Because the generalized form of demodectic mange may due to a genetic defect in the immune system, affected dogs should not be bred, and the parents of the affected dog should not be bred again.
What are the signs of demodectic mange?
Dogs with demodectic mange experience patchy hair loss, often without severe itching.
- Localized demodex causes hair loss, commonly on the face and front legs.
- Generalized demodex causes hair loss in many different areas of the body, especially the paws.
Although demodex overgrowth doesn’t tend to cause itching, itching may occur if dogs develop skin infection secondary to the overgrowth.
How is demodectic mange diagnosed?
Your veterinarian will take deep skin scrapings and examine them under the microscope to diagnose this disease. If higher-than-normal numbers of Demodex mites are found in the skin scrapings, the diagnosis is confirmed. Occasionally, demodectic mange is diagnosed through a skin biopsy, particularly in dogs with chronic skin infections that have not responded appropriately to treatment.
How is demodectic mange treated?
Demodex mites are killed effectively by several oral or topical anti-parasitic treatments, including:
- Isoxazolines, such as afoxolaner (Nexgard®), fluralaner (Bravecto®), sarolaner (Simparica®), and lotilaner (Credelio®)
- Macrocytic lactones, such as moxidectin (Advantage Multi®), ivermectin, milbemycin oxime, and doramectin (Dectomax®).
In some cases, these medications are used off label, which means they are not approved for demodicosis treatment but are accepted as being safe and effective. In some cases, your veterinarian may choose one product over another based on the risk of your dog having a multidrug resistance mutation (ABCB1 or MDR1). This genetic mutation may make your dog more sensitive to side effects of certain products.
Treatment for demodectic mange used to primarily involve cleaning the dog with special shampoos containing benzoyl peroxide, which helps to flush out and open the hair follicles, and then “dipping” in a strong insecticide called amitraz. This treatment is used much less frequently now, because of the potential side effects and the development of safer medications.
In some cases, especially dogs with generalized demodectic mange, secondary skin infections complicate the condition and require antibiotic or shampoo therapy. These skin infections often cause red, inflamed skin, so demodectic mange is often called “red mange.” Your veterinarian will determine if your dog has a skin infection in addition to demodectic mange.
What is the prognosis?
Treatment of demodectic mange is generally successful. However, if the immune system is weakened, neither the mites nor the infection may respond to treatment. With generalized demodicosis, successful treatment may take a long time and may require regular skin scrapings to assess treatment progress.
A dog with demodectic mange may have relapses until they are 12 to 18 months old because the immune system does not mature until that age. In addition, dogs with suppressed immune systems may be susceptible to relapse. It is important to treat as soon as a relapse occurs to minimize the possibility of developing uncontrollable problems. Relapses usually occur three to six months after treatment is discontinued.
