Demodectic Mange in Dogs

Many animals have diverse communities of microorganisms inhabiting their skin. This includes helpful bacteria, fungi and yeast, and sometimes microscopic mites. These tiny arthropods feed on dead skin cells and sometimes skin secretions, but usually do no harm as they are kept in check by the immune system. However, Demodectic mange is a condition where the immune system has failed to suppress the populations of mites, which are allowed to colonize the hair follicles in large numbers. Their actions of feeding and defecating irritates the skin and may allow opportunistic bacteria to cause infection. This causes inflammation, scarring and hair loss. Contact a veterinarian if your dog develops hairless patches, even without noticeable itching or discomfort.

Demodectic mange is a condition caused by excessive populations of a normal skin mite, Demodex canis. This mite is part of the normal microscopic community on the skin and is not normally a threat to health. However, when the immune system of an animal becomes compromised, these mites are allowed to invade the hair follicles in much greater numbers, leading to hair loss and skin irritation. It can occur in several different forms affecting both young and old animals.

• Hairless patches
• Excessively oily skin
• Redness or inflammation
• Swelling of the paws
• Crusting of the skin.

• Congenital immune system deficiency
• Age related decline in immune system
• Idiopathic mange
• Drug-induced immune deficiency

Types

• Juvenile Immunodeficiency
• Localized Mange
• Adult Onset Immunodeficiency

Owners who notice their pet developing bald patches, excessive skin oiliness and irritation should see a veterinarian as soon as possible, as the condition is easier to treat if it is caught before symptoms become too severe. Demodectic mange is easily diagnosed with a microscopic examination of either a scraping of the skin, or a few plucked hairs. This will reveal the mites, eggs and larvae. Unfortunately, diagnosing the underlying condition that has allowed the mite population to expand is not so easy.

The first category of demodectic mange is hair loss in small patches most commonly located around the lips, eyes and legs. These patches may exhibit redness and scaling, and usually occur in dogs less than a year old. While this kind of mange may resolve on its own, your veterinarian can provide topical creams to make sure the condition doesn’t spread.

If this condition is allowed to spread, or the dog has an immune deficiency, this can progress to juvenile-onset generalized demodecosis. This condition is often the result of an inherited condition in which the cell-mediated immune system does not work properly to identify and combat foreign invaders. Generalized demodecosis is a severe illness causing hair loss over the entire body along with skin irritation and pustules. Fever and inflammation are often seen with this condition.

In older dogs, a similar condition can occur, but indicates either a medication or underlying condition is compromising the immune system. Cancers such as lymphosarcoma, melanoma can suppress the immune system, along with diseases like Cushing’s and diabetes. Sometimes, this condition is idiopathic, meaning no underlying condition is found, and the reason for the mange is not known.

Demodectic mange that is not related to an immune deficiency is easily treated with a number of anti-mite creams, or simply left to heal on its own. Trimming the hair around the affected areas if it is extremely thick helps with medication penetration, and benzoyl peroxide shampoo can rapidly correct the condition.

For generalized demodecosis, whole-body treatments with benzoyl peroxide or amitraz may be needed, along with anti-parasitics such as ivermectin. Note that ivermectin should never be given to Collies and Collie crosses, as it is potentially toxic. Any bacterial infections should be treated with an appropriate antibiotic.

Sometimes, anti-inflammatory drugs or corticosteroids can depress the immune system enough to allow the mite population to grow out of control. Use of the above treatments in addition to stopping the anti-inflammatory drugs is usually curative.

The outlook for dogs with immune disorders is mixed. Dogs with juvenile-onset mange may be susceptible to other diseases that can be fatal, or experience infections leading to sepsis. In general, any dog with a suspected immune deficiency should not be used for breeding. Older dogs experiencing immune deficiency due to cancer will have an outlook dependent on the cancer location and type as well as treatment pursued.

Dogs without immune disorders, or dogs being treated with anti-inflammatories usually experience a complete correction of the disorder upon treatment with topical creams and shampoos along with cessation of any immune-suppressing medications.