Demodicosis, Demodectic Mange or Red Mange

Filed Under: Dogs, Parasites

Does your dog have patchy areas of hair loss, especially around the head and front legs? Are the affected skin areas red and irritated? Is your dog under two years of age? Then your pet could be suffering from demodectic mange.

Demodicosis is caused by three different species of small cigar-shaped mites which may only be detected through the aid of a microscope. Demodex canis is the most commonly diagnosed species and is confined to the hair follicle, and rarely, the sebaceous glands of the skin. Demodex injai is a larger species of mite which resides within the sebaceous glands. The third species, Demodex cornei, prefers to situate itself in the most superficial layer of the epidermis. D. cornei is 50% shorter than the adult form of D. canis. All of these mites are obligatory parasites of a dog’s skin. The entire life cycle of this parasite is spent on the affected dog.

A very small number of D. canis mites may be found on normal skin. In fact, even humans may have one or two mange mites located in their eyebrows. Demodicosis, as a clinical syndrome, results when the mites proliferate beyond the capacity of the host’s immune system to control the mite population on their skin. The specific genetic defect is as yet unknown but is believed to be an autosomal recessive gene that allows for overgrowth and proliferation of the mites.

Puppies acquire D. canis mites from their dams (female parent) while nursing in the first 2 to 3 days of life. Most cases of juvenile demodectic mange occur between three and six months of age.

Demodicosis typically comes in one of two syndromes: localized or generalized. Localized demodicosis is typically a mild condition involving only one to a few skin sites that heal spontaneously in 6 to 8 weeks. Lesions typically begin around the eyes, mouth, and over body projections on the extremities, especially the forelegs. The affected areas may vary in size for weeks to months before finally resolving. Mupirocin, also known as Goodwinol ointment®, or benzoyl peroxide gels such as OxyDex® or Pyoben®, are often used to treat the localized areas topically, although anecdotally, there does not appear to be a difference in response between treated and untreated cases.

Demodicosis is considered to be generalized when a pet has five or more localized lesions, involvement of an entire body region, or involvement of two or more paws. Generalized demodicosis tends to occur when the dog is from 3 to 18 months of age.    Affected male animals should be neutered. It is strongly recommended that intact female dogs undergo ovariohysterectomy not only due to the genetic component suspected in transmission, but also because the stress of a heat period may result in clinical relapse.

Skin pathology includes hair loss, redness, resulting in the term “red mange,” and hyperpigmentation. Secondary skin infections, or pyoderma, are characterized by nodules, erosions, bloody crusts, and draining tracts. Demodicosis may occur with or without pruritus (itching). Characteristically, the more pruritic infections will have concurrent secondary bacterial infections. Infections with D. cornei are also often more pruritic.

Demodicosis is the most prevalent cause of deep bacterial pyoderma in dogs, with the most commonly isolated bacteria being Staphylococcus intermedius. These animals may be painful, have peripheral lymph node adenopathy (swelling), have elevated temperatures, and draining tracts. Life-threatening secondary infections may develop in severe cases due to the threat of sepsis. Antibiotic therapy is typically conducted for 3 to 8 weeks.

Demodex canis may also cause a chronic ceruminous (wax producing) ear infection which may occur with or without other skin areas being affected.

A rare form of the red mange, known as adult-onset demodicosis, occurs when a dog has its first bout of demodectic mange at over four years of age. This syndrome is just as severe as the juvenile form. Adult-onset demodicosis characteristically occurs when there is an underlying suppression of the immune system in these animals. Complicating diseases such as hyperadrenocorticism, hypothyroidism, systemic diabetes mellitus, neoplasia, etc. may result in the immunosuppression necessary to induce a clinical case of adult-onset demodicosis. The administration of systemic or topical immunosuppressive drugs may both trigger cases of adult-onset demodicosis.

Demodicosis may also occur as dermatitis confined to the paws or feet, termed pododemodicosis. Old English Sheepdogs are more commonly affected with this problem than are other breeds. Demodicosis clears on all areas except the feet, requiring residual treatment in these areas.

A diagnosis of demodectic mange may be easily confirmed through a skin scraping. Diagnosis is made by demonstrating the immature or adult mites on microscopic examination. The dog should be scraped in several areas so that the mites are not missed. Hair may also be examined near lesion margins. Plucked hairs are less sensitive in picking up the mange mites but are useful when skin lesions are found near sensitive areas of the face and paws.

On rare occasions demodectic mites may be missed even on carefully conducted skin scrapings. This is especially common when taking a skin scraping from a pet with thickened and fibrotic skin due to chronic infection. Mites may also be hard to detect in certain breeds such as the Shar-Pei and the English bulldog -- especially when lichenification (thickened and darkly pigmented skin) is present in affected skin areas. If demodicosis is still strongly suspected after negative skin scrapings are conducted a skin biopsy is recommended for histological examination.

Shampoos containing benzoyl peroxide provide follicular flushing and excellent antibacterial activity. Following shampoo, the only drug approved for the treatment of demodicosis is Mitaban®, available from Pfizer Animal Health, or Ectodex®, both of which are amitraz dips that are applied topically and not rinsed off. These dips are given at two week intervals. Cure rates with amitraz range from 60% to 80% in juvenile-onset cases but up to 94% of all affected pets may be cured with intensive treatment, extended treatment regimens, or residual dips. The average treatment time to clinical and microscopic remission typically takes a course of six dips. The most common cause for treatment failure is premature cessation of therapy, bathing or swimming between dip treatments, and the concomitant use of glucocorticoids or other immunosuppressive drugs.

The side effects of amitraz treatment may include depression, ataxia, diarrhea, bradycardia (slow heart rate), a below normal rectal temperature, and hyperglycemia. A transient erythematous rash has also been observed. Treatment with Atipamezole at a dose of 50µg/kg given intramuscularly can reverse these signs of toxicosis within 10 minutes or the dip may be washed off and the pet will gradually return to normal.

Just recently a new spot-on flea and tick formula containing metaflumizone and amitraz, sold by the name of ProMeris®, is available from Pfizer for the treatment of demodectic mange. When used topically every 14 days, juvenile-onset demodectic cases showed a 92.3% reduction in mite numbers. The largest complaint with treatment has been the product’s odor. Other side effects may include a transient lethargy, vomiting, diarrhea, or allergic skin reactions.

Although not approved for the treatment of demodicosis, ivermectin and milbemycin have both been used to control chronic generalized demodicosis. Animals must be heartworm negative before beginning treatment. Ivermectin-sensitive dogs, such as herding dogs, should not be treated unless they have been determined not to have the MDR1-1 genotype in their genetic makeup. Animals with the MDR1-1 gene will develop a severe neurotoxicosis after just one dose of ivermectin. Testing for the MDR1-1 gene is available through Washington State University’s Veterinary Clinical Pharmacology Laboratory. Dog breeds sensitive to ivermectin will generally tolerate milbemycin oxime. Treatment with ivermectin and milbemycin for demodicosis is considered to be an extra-label usage and is typically reserved for those pets who do not respond to amitraz dips.

Another recently available product, Advantage Multi®, developed by Bayer Animal Health, is being marketed for heartworm prevention as well as for flea and intestinal parasite control. This product was tested on demodex mites and found to be very effective topically in the elimination of the parasite. Again, pets should be found to be heartworm negative before starting treatment with this drug and are advised that the use of this drug in mite control is considered to be an extra-label use.

For the treatment of demodectic otitis (infections of the ear) a 0.1% solution of milbemycin oxime, marketed under the trade name MilbeMite®, is available from Novartis Animal Health, but again this is considered to be an extra-label usage. Pododemodicosis and demodectic otitis may both be treated with an extra-label mixture of amitraz and mineral oil utilizing one part amitraz to 9 parts mineral oil, or a 1:10 dilution.

If all other treatments fail, several EPA registered pesticides that are not approved for treatment in the dog have been tried. One of the oldest treatments is to mix up a 3% solution of trichlorfon, available from Miles Laboratories. The solution is then applied to one-third of the animal’s body on a rotating basis by painting the mixture on. Severe toxicities characteristic of an organophosphate poisoning may occur.

Typically two consecutive skin scrapings with negative results two weeks apart are considered necessary to discontinue treatment for Demodex. A pet is deemed cured if no relapses are shown to occur with 12 months of discontinuing treatment for the mites.

The breeds with the highest frequency of demodicosis cases include the following:
Shar Peis, West Highland white terriers, Scottish terriers, English bulldogs, Boston terriers, Great Danes, Weimaraners, Airedale terriers, Alaskan Malamutes, and the Afghan hound. Any breed other than a hairless variety may develop demodicosis.

References:

Georgi, Jay and Marion Georgi. Parasitology for Veterinarians. W.B. Saunders. 5th Edition. 1990. Pp. 66-67.

Moriello, Karen. Clinical Snapshot. Compendium Continuing Education Veterinarians. Vol. 30(7), July 2008. Pp. 370 and 403.

Rosenthal, Marie. “New Option for Treating Canine Demodectic Mites.” Veterinary Forum. May 2009. Pp. 22-25.

Tater, Kathy, and Adam Patterson. “Canine and Feline Demodicosis.” Veterinary Medicine. August 2008. Pp. 444-461.

Scott, Danny, and William Miller, et al. Muller & Kirk’s Small Animal Dermatology. 5th Edition. W.B. Saunders Company. 1995. Pp 417-432.

Mueller, Ralf. “Demodex Canis Control in Dogs.” NAVC Conference, January 2008.
Pp. 13-17.

Poisker, Ronald, DVM. “Severe Deep Pyoderma Secondary to Generalized Demodicosis.” Veterinary Forum. August 2007. Pp.20-21.

Topics: demodectic mange, mange

Symptoms: hair loss, irritated skin, itching, scratching

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