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Summary
Demodicosis is a common skin disease in dogs. Also referred to as "red mange," it occurs as the result of a species of mites known as Demodex. Unfortunately, however, the disease state is far more complex than that of a simple parasitic infestation. That's because this disease is largely characterized by the interaction between the animal's immune system and the demodectic mange mites.
There are three recognized species of Demodex mites. While the most commonly observed is the Demodex canis, which is a normal inhabitant of dog skin, Demodex injai and Demodex cornei may also be identified.
Two different disease states are typically recognized under the umbrella of demodicosis:
Juvenile-onset demodicosis typically occurs in dogs that are under eighteen months of age. It can be further subdivided depending on whether the lesions are localized to certain spots or generalized. The generalized version is typically considered more severe. It's defined as demodicosis that a) affects the feet or an entire region of the body, b) spreads, or c) persists for six months or more. This version of demodicosis has been correlated with poor nutrition, stress, and genetics.
Adult-onset demodicosis is defined by onset only after a dog achieves maturity. It tends to occur in the case where dogs are suffering systemic diseases. Cushing's disease (hyperadrenocorticism), hypothyroidism, diabetes, and certain cancers can predispose dogs to this version of demodicosis. Alternatively, immunosuppressive drug therapies (such as corticosteroids and chemotherapeutics) can bring on this condition.
Concurrent skin diseases, such as allergic skin disease (in particular), can also influence the course of demodicosis in both its juvenile- and adult-onset varietals.
Though treatable, canine demodicosis is nonetheless considered a highly frustrating dermatologic condition due to its variable response to treatment and the often lengthy (and expensive!) course of treatment required.
Demodicosis is also a recognized problem in cats. Though much less well understood, new species of Demodex are being investigated in felines. The remainder of this article, however, will be confined to the discussion of canine demodicosis alone.
Symptoms and Identification
In dogs, the most common clinical sign observed in demodicosis patients is hair loss. Discrete spots of missing hair, a moth-eaten or patchy appearance to the coat, or sometimes even hair loss over the feet or an entire region of the body (the flanks, for example) can be observed. Other signs include:
scaling
crusts
papules (little red welts)
comedones (blackheads)
redness
darkening of the skin
thickening of the skin.
Itchiness may or may not be a factor. If the demodicosis is more longstanding, it's more likely to be itchy because of secondary infections (yeast and bacteria, typically) that may take advantage of the skin's depleted condition.
In severe cases, deep skin infections can occur. These can lead to systemic signs of illness (such as fever, lethargy and poor appetite). Ear infections, too, may result.
Demodicosis is usually diagnosed by identifying the mites via microscopy. Examining skin scrapings and/or hair pluckings is the most commonly undertaken method of mite identification.
Impression smears, acetate tape preparations, and exudate samples of the skin are also useful to test for the presence of secondary infections that may be complicating the disease process. Otic swabs are indicated in the presence of ear involvement. Culture and sensitivity may also be required in the case of deep skin or ear infections.
Any dog with generalized juvenile-onset demodicosis or adult-onnset demodicosis should be thoroughly evaluated for the presence of systemic disease. Complete blood count (CBC), serum biochemical analysis (chemistry panel), urinalysis, and thyroid testing are generally considered basic tests for these patients. Allergy testing and testing for specific immunosuppressive conditions are also recommendable.
It's important to note that different species of mites may lead to different patterns of disease.
Affected Breeds
Any breed of dog can be affected by juvenile-onset demodicosis. Some breeds, however, may be predisposed. Reports vary, but according to some literature, demodicosis appears to be overrepresented among Staffordshire Bull Terriers, German Shepherd Dogs, Old English Sheepdog, Collies and Dalmatians.
Theoretically, dogs pertaining to breeds that are predisposed to Cushing's disease (hyperadrenocorticism), hypothyroidism, diabetes, and any other disease that can lead to adult-onset demodicosis are predisposed to it. No specific breed predisposition has been outlined otherwise.
Treatment
Topical therapy typically involves the use of shampoos, dips and/or ointments.
Oral medications often include antibiotics to treat secondary infections and parasiticides to kill the mites themselves.
Treatment of the underlying systemic disease, if identifiable, is always crucial to the long-term success of adult-onset demodicosis. Discontinuing the use of any immunosuppressive drugs is essential as well.
Veterinary Cost
Because definitive diagnosis is relatively simple in uncomplicated cases of localized juvenile demodicosis, it's considered relatively inexpensive to diagnose, at typically less than $50 to $100.
Unraveling the mysteries of complicating factors, underlying diseases and perpetuating conditions common to generalized juvenile demodicosis and adult-onset demodicosis, however, can prove complex and, consequently, expensive. Given that allergy testing alone can run into the high hundreds or more, it's understandable that more difficult cases of demodicosis can seem unaffordable for some.
Treatment of localized juvenile demodicosis is also relatively inexpensive as many cases respond favorably to shampoos and antibiotics, never necessitating further intervention beyond a $50 vial of antibiotics, a $40 bottle of shampoo, and the personal investment of some at-home manpower.
Recalcitrant cases of localized juvenile-onset demodicosis, generalized juvenile-onset demodicosis and adult-onset demodicosis, however, can be far tougher to treat. As these will invariably require longer courses of potentially expensive mite killing drugs and sometimes in-hospital treatments for weeks (or months) at a time, the fees can add up. Over time, it's not unusual for owners to see expenses run into the thousands.
The cost of any underlying or exacerbating conditions must also be factored into this equation when it comes to treating most complicated cases of demodicosis.
Prevention
Prevention generally isn't considered feasible for demodicosis patients.
References
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Desch CE Jr, Stewart TB. Demodex gatoi: new species of hair follicle mite (Acari: Demodecidae) from the domestic cat (Carninvora: Felidae). J Med Entomol 1999;36(2):167-170.
Gortel K. Update on canine demodicosis. Vet Clin North Am Small Anim Pract 2006;36(1):229-241.
Holm BR. Efficacy of milbemycin oxime in the treatment of canine generalized demodicosis: a retrospective study of 99 dogs (1995-2000). Vet Dermatol 2003;14(4):189-195.
Kwochka KW, Kunkle GA, O'Neill Foil C. The efficacy of amitraz for generalized demodicosis in dogs: a study of two concentrations and frequencies of application. Compend Contin Educ Pract Vet 1985;7:8-17.
Medleau L, Brown CA, Brown SA, et al. Demodicosis in cats. J Am Anim Hosp Assoc 1986;24:85-91.
Mueller RS, Bettenay SV. A proposed new therapeutic protocol for the treatment of canine mange with ivermectin. J Am Anim Hosp Assoc 1999;35(1):77-80.
Mueller RS. Treatment protocols for demodicosis: an evidence based-review. Vet Dermatol 2004;15(2):75-89.
Robson DC, Burton GG, Bassett R, et al. Eight cases of demodicosis caused by a long-bodied Demodex species (1997-2002). Aust Vet Pract 2003;33(2):64-72.
Saridomichelakis MN, Koutinas AF, Farmaki R, et al. Relative sensitivity of hair pluckings and exudate microscopy for the diagnosis of canine demodicosis. Vet Dermatol 2007;18(2):138-141.