Demodicosis is an inflammatory parasitic disease characterized by the presence of greater than normal numbers of demodex mites in the hair follicles and on the skin. The reason for this proliferation is poorly understood but a genetic defect in the T-cell portion of the immune system is suspected. 

There are two forms of demodicosis:  

• Localized

Localized demodicosis lesions are typically characterized as focal areas (3 or less and in one region) of mild erythema (redness) with partial alopecia (hair loss) and variable amounts of scale. The most frequently affected areas of the body are the periocular (around the eye) and perioral (around the mouth) regions with the forelegs and the trunk as the second most common sites. Most localized demodicosis cases are mild and regress spontaneously; however, approximately 10% of cases will progress to the generalized form.  

• Generalized

The generalized form is characterized as juvenile onset (dogs less than one year of age), adult onset, and pododemodicosis (affecting the paws). Generalized demodicosis can be quite severe and the lesions exhibit erythema (redness), alopecia (hair loss), crust formation, scale, and exudation. Pruritus (itchiness) is variable. Some dogs may have pododemodicosis (paws) only without involvement of other sites. Secondary pyoderma (bacterial infection) is a consistent feature of generalized demodicosis.

Treatment

• Localized Demodicosis

Treatment of localized demodicosis is not always necessary as the majority of cases will spontaneously resolve. Treatment will not prevent progression to the generalized form. The general health status of the patient should be evaluated (ie. intestinal parasitism, diet, etc.) to ensure that underlying abnormalities or conditions do not contribute to the animal's predisposition to demodicosis. Topical therapy is frequently used for localized lesions.

• Generalized Demodicosis

Therapy for generalized demodicosis requires dedication over an extended period of time. In many cases, only control of the disease may be established rather than a complete cure or resolution. The following steps may be recommended for the treatment of generalized demodicosis:

• Shave the pet (long haired pets) if the skin is markedly crusted and exudative
• Gently remove all heavy crusts from the skin
• Protect the eyes with ophthalmic ointment
• Shampoo the dog with a benzoyl peroxide shampoo and / or soak in a whirlpool bath with an antiseptic solution
• Towel dry
• Repeat once or twice weekly
• Systemic antibiotics should be given for an extended period of time 
  
  

Medical Therapy Options

• Ivermectin - currently approved as a heatworm preventative, it is also used at a higher dose to treat demodicosis. This medication has been reported to cause side effects in some breeds (Collie, Sheltie, Old English Sheepdog).
  
  Side effects include tremors, muscle weakness, dilated pupils, vomiting, diarrhea and seizures. The use of Ivermectin (in breeds other than those recognized as being sensitive) is common practice in veterinary dermatology. Ivermectin is considered one of the most effective forms of therapy in the treatment of demodicosis. Testing for Ivermectin sensitivity can be done in advance of prescribing therapy.  
  
  The dose is often lowered (test dose) during the first week of therapy to allow the opportunity to observe for adverse reactions. The dosage is adjusted upward if no ill effects are observed. 

• Mitaban dips (Amitraz) - a dip that is applied topically to the skin on a weekly or every other week basis. Small dogs may experience marked lethargy for 12 to 24 hours after application. The dip should be applied in a well-ventilated area. It is often difficult to effectively apply the dip to certain affected areas such as the face. This dip is not readily available in the U.S.

• Promeris spot-on (Amitraz) - similar side effects as noted with the topical dip (Mitaban), although there have also been reports of Pemphigus like reactions secondary to the use of this product. It is no longer readily available.

• Interceptor (milbemycin) - a medication commonly used for the prevention of heartworm disease. Ivermectin sensitive breeds often tolerate this medication. Side effects are similar to Ivermectin (depression, ataxia (wobbly gait), seizures).

LymDip (lime sulfur dip) - this protocol is the treatment of choice for cats (not dogs). Lime sulfur dips are very safe yet quite messy and malodorous. Cats must be prevented from licking the fur while wet from the dip as it may cause oral irritation.

Bravecto, Advantage Multi, etc.: the list of potential medications seems to change monthly

Prognosis

Prognosis depends on a number of factors including the severity of the condition, age of onset, duration of disease, and presence of underlying disease. Adult onset demodicosis is often difficult to treat and may require long-term therapy. It is recommended that affected young dogs be eliminated from the breeding population (castration / spay) to prevent any hereditary propensity.

Follow Up

Monthly or every-other-month recheck appointments are important to monitor the progress of the disease. It is essential to perform frequent skin scrapings and / or trichograms, as many dogs may look “cured” and still have mites that are microscopically visible. It is often recommended that the pet be treated for at least one month after a negative sample.

Contributed by:  Karen Helton-Rhodes, DVM, Diplomate ACVD

Illustration reprinted with permission by the copyright owner, Hill’s Pet Nutrition, Inc.