Dog Mange - Demodectic

Introduction

Demodectic mange in domestic dogs is an inflammatory skin disease caused by tiny mites of the Demodex canis species. It is also called demodicosis, demodex, red mange or follicular mange. These mites are too small to be seen with the naked eye. They normally are present in very small numbers in the hair follicles and sebaceous glands of healthy dogs. Sebaceous glands are those that secrete a substance called "sebum," which is the oily secretion coming from sebaceous gland ducts that open into the hair follicles. Sebum is made of fat and skin debris and functions to lubricate and moisturize the skin. Demodectic mange develops when the affected dog's immune system is suppressed, weakened or otherwise compromised such that it cannot keep the rise of these mites at bay.

Causes & Prevention

Causes of Demodectic Mange
Demodicosis in dogs is caused by tiny parasitic mites of the species, Demodex canis. These mites live deep inside the hair follicles and sebaceous glands of the skin of host dogs. Demodex canis mites are considered to be part of the normal flora of the skin of dogs and typically are present in small numbers without causing any noticeable symptoms. In fact, almost all puppies acquire these mites directly from their mothers within the first few days of life. The immune systems of healthy dogs usually suppress excessive proliferation of the mites, which in turn prevents any obvious adverse reactions from their presence. However, dogs with weakened immune systems can develop clinical signs of demodectic mange, because the mite population gets out of control. In other words, the immune system does not respond properly to the normal presence of the Demodex mites. It is thought that genetic influences play a strong role in a dog's development of demodicosis. This theory is supported by the fact that purebred dogs from certain breeds and bloodlines are more likely to develop demodectic mange than are other dogs.

In most cases, demodicosis is localized, meaning that it causes patchy, non-itchy hair loss on only a few areas of the dog's body. However, demodicosis can also become generalized, with hair loss and lesions (sores) across most or all parts of the dog. Generalized demodectic mange can be a very serious medical condition that unfortunately often is resistant to treatment.

Prevention of Demodectic Mange
Many authorities recommend not breeding dogs that have been affected by either localized or generalized demodectic mange, because of the suspected hereditary component to its cause. Vaccinations, heartworm infection, administration of corticosteroids and estrus (going through a heat cycle) have all been reported to potentially exacerbate Demodex infections, probably because they suppress dogs' immune systems for a period of time.

Special Notes
The precise mechanism that permits Demodex mites to proliferate in some dogs but not in others is unknown. Certainly, it is thought that genetics play a role. Adult dogs that develop generalized demodicosis usually have some underlying systemic disease that suppresses or weakens their immune system, allowing the mites to reproduce without control. In puppies, the localized form is much more common and usually resolves over time.

Symptoms & Signs

How Demodectic Mange Affects Dogs
Juvenile dogs with localized demodectic mange typically are not itchy (pruritic) and do not seem to be painful. They have mild patchy hair loss that usually appears on one or only a few places on their body. However, they do not seem to suffer at all as a result of the presence of the Demodex mites. In fact, other than the cosmetic changes in their appearance, they act and appear completely normal. When dogs develop generalized demodicosis, with widespread hair loss and sores all over their bodies, they often do become itchy and painful. If this happens, they may scratch, chew or bite at their infected areas, causing self-trauma and sores (lesions) that can become secondarily contaminated and infected by bacterial or other microorganisms.

Symptoms of Demodectic Mange
Most cases of demodectic mange usually are localized, which means that the patchy hair loss (alopecia) appears only in several limited or confined areas on the dog's body. Sometimes, the disorder becomes multifocal, meaning that there are defined areas of patchy hair loss that show up on many different areas of the dog's body. When demodectic mange becomes generalized, it is a much more serious medical condition.

Owners of dogs with demodectic mange may notice one or more of the following signs of this condition, usually in young dogs between 3 and 6 months of age but occasionally in middle-aged to older adult dogs:

Patchy hair loss (alopecia) anywhere on the body, but most commonly localized to the head, face (lips, muzzle, around the eyes), neck, front legs and/or shoulders. The patches of thinning hair are usually about 1 inch in diameter. This is commonly referred to as a "moth-eaten" appearance. Juvenile focal demodicosis typically resolves spontaneously within a matter of weeks to months, whether or not it is treated.
Generalized patches of hair loss in patches that coalesce or merge to form large areas of sores and draining tracts all over the dog's body.
Scabbing, scaling, inflammation and crusting of the skin in one or many places
Skin infection (redness, rawness, presence of pus)
Plugged hair follicles
Patchy hair loss in middle-aged to older dogs; almost always associated with some other systemic disease and/or immunosuppression
Itchiness (pruritis) (+/-; more common with generalized demodectic mange than with the localized form)
Scratching at affected areas
Skin redness (erythema)

Dogs at Increased Risk
Certain domestic dog breeds are predisposed to developing demodectic mange. According to many authorities, these include the Afghan Hound, American Pit Bull Terrier, American Staffordshire Terrier, Boston Terrier, Boxer, Collie, Chihuahua, Dalmatian, Doberman Pinscher, English Bulldog, German Shepherd Dog, Great Dane, Old English Sheepdog, Pug and Shar-Pei.

Diagnosis & Tests

How Demodectic Mange is Diagnosed
The most reliable way to diagnose demodectic mange is by taking multiple skin scrapings. Of course, the veterinarian will first get a history from the owner about the dog's health and symptoms and then will conduct a thorough physical examination. Skin scrapings are just what they sound like: physical scrapings of the areas of patchy hair loss. The veterinarian will squeeze the affected areas to encourage the mites to come out of the hair follicles. He then will use a sharp sterile scalpel blade to scrape fairly deeply into at least 4 or 5 of those sites, to the point of drawing a small bit of blood. The samples of the scrapings will be placed onto glass slides and examined under a microscope. Demodex mites usually can be readily identified through this process. They have a unique shape, size and profile that are easily recognizable microscopically. It is important to examine scrapings from several different locations, because each patchy area may not have the same number of adult mites proliferating at any given time.

In some cases, the veterinarian may recommend taking actual skin biopsies instead of superficial skin scrapings to confirm a diagnosis of demodectic mange. For example, this is commonly done in Shar-Peis, because of their thick, coarse skin. Skin biopsies may also be recommended for dogs whose feet are affected by the mites (this is called pododermatitis).

Special Notes
Adult dogs that present with signs of demodectic mange should also be evaluated for evidence of systemic disease. A systemic illness is one that affects or pertains to the body as a whole, as opposed to one that affects only certain organs, areas or body systems. Typically, the search for systemic disease will involve a urinalysis, routine blood work (a complete blood count and serum biochemistry profile), abdominal and thoracic (chest) radiographs (X-rays) and screening tests for thyroid, endocrine and other metabolic disorders. More advanced testing may also be appropriate.

Treatment Options

Treatment Options
Demodicosis can be challenging to treat, under even the best of circumstances. The therapeutic goal is to resolve the hair loss, scaling, crusting, redness, rawness and other skin symptoms associated with the condition. The key to a good outcome is early identification of the problem and consistent treatment with oral and topical products. Many if not most cases of localized juvenile demodectic mange will resolve spontaneously as the puppy's immune system matures, with or without treatment. Over time, the immune systems of most healthy dogs are able to suppress abnormal proliferation of Demodex mites. Still, most owners of dogs identified as having demodicosis choose to treat their dogs rather than simply hope and wait for the infestation to resolve.

There are several ways to treat demodectic mange. Currently, daily doses of oral ivermectin, milbemycin or moxidectin, and/or frequent periodic dips with Amitraz (brand name Mitaban), continued over a number of months, are the treatments of choice. Not all of these treatment protocols are officially labeled or approved for use in dogs with this disorder. Benzoyl peroxide gels and shampoos can be helpful to loosen the hair follicles and flush out the mites from specific patchy areas. The affected skin areas should be clipped or shaved to facilitate penetration of the medication into the hair follicles. Monthly skin scrapings will help the veterinarian and owner monitor the dog's response to treatment. Most authorities recommend continuing treatment until the animal no longer has any obvious signs of mange, and then slowly weaning them off of the oral and/or topical medications over a period of 30 to 60 days additional days.

Oral vitamin E supplementation has been described as an adjunct to standard therapy, although there is no reliable scientific evidence proving that it helps to resolve cases of demodectic mange. If dogs develop secondary bacterial skin infections (pyoderma) as a result of demodicosis, the veterinarian will prescribe a course of antibiotics until the infection is resolved. Corticosteroids, which are often used to control severe itchiness, probably should not be used in dogs with demodectic mange, because they function in part by suppressing the animal's immune system. Of course, new treatments are always under development. Owners of affected dogs should consult closely with their veterinarians to be sure that they are receiving the most up-to-date therapy that is available.

It is important for owners to recognize that treatment with ivermectin can have some potentially serious adverse side effects. Most of these are neurological in nature and include weakness, disorientation (ataxia), excessive salivation, collapse, coma and possibly even death. Collies and Collie crosses have a greatly increased risk of having bad side effects from being treated with ivermectin. Amitraz (Mitaban) can also have unpleasant side effects, including sedation, drowsiness, lethargy, depression, itchiness (pruritis), vomiting, diarrhea, dizziness, hyperglycemia and a staggering gait.

Prognosis
The prognosis for dogs with demodectic mange is quite variable. As treatment progresses, if skin scrapings reveal an increasing number of dead mites and a decreasing number of juvenile mites, the outlook is promising. Young dogs with localized juvenile demodicosis typically have quite a good prognosis and, with or without treatment, usually recover with no adverse repercussions from the condition. Adult dogs that develop demodicosis are much less likely to recover spontaneously and tend to have a more guarded prognosis. Approximately 10% of affected dogs will never be cured and will require medical management for life. However, if the owner is willing to commit the time, energy and cost of intensive treatment for a dog with demodectic mange, that dog probably will be able to live a full, content and happy life without suffering many if any adverse consequences from the mites.