Canine demodicosis: Serious disease requires aggressive therapy - DVM
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Canine demodicosis: Serious disease requires aggressive therapy


DVM360 MAGAZINE



Photo 2: Focal area of demodex in the medial canthal skin of a young Labrador Retriever.

Photo 3: Focal area of erythema and alopecia on the muzzle of a German Shepherd with focal demodex.














The diagnosis of demodicosis is made by squeezing the affected skin, then performing deep skin scrapings or hair plucks to observe them in oil under low power.

Occasionally skin biopsies are necessary in cases of mites that reside deep in hair follicles or sebaceous ducts. This most often occurs in the Shar pei and when demodex of the feet are present (either one foot or all four may be affected). Also advisable is a complete blood count, serum profile, urinalysis, fecal exam and heartworm test with possible thyroid panel, ACTH stimulation test and chest/abdominal radiographs if dealing with adult-onset disease.

Treatment options for juvenile- or adult-onset demodicosis include steroid avoidance either systemically or topically, bathing in a follicular flushing shampoo such as benzoyl peroxide, and antibiotic therapy for the concurrent bacterial pyoderma.

Total body clipping may be required in long-haired dogs to facilitate dipping if that method of treatment is elected. One of the acaricide treatments below may be used (do not combine therapies):

  • Amitraz dips: The only FDA-approved therapy for generalized demodicosis. Amitraz is an alpha-2 agonist, monoamine oxidase inhibitor (MAOI) and prostaglandin inhibitor. The dip should be diluted according to manufacturer's directions, for example, one bottle/2 gallons water (0.025%). Biweekly applications in one study resulted in a 22 percent cure rate versus a 78 percent cure rate using weekly applications. The dips should be continued until negative skin scrapings followed by two to four dips beyond that. There is minimal increased efficacy with increasing the concentration when compared with adverse side effects. (A French study used a 1.25% concentration weekly and was 100 percent effective in patients refractory to previous amitraz therapy). The dips should be preceded by a follicular flushing shampoo such as benzoyl peroxide without bathing between dips. Side effects include sedation, bradycardia, polyuria, hypothermia, hyperglycemia and hypotension. Avoid amitraz use with concurrent MAOIs such as doxepin or antihypertensives. Pruritus and erythema following a dip is usually the result of the mites dying off. A fecal analysis may contain many dead demodex mites. Reactions to amitraz should be treated supportively. Yohimbine has been used preceding dips in some sensitive individuals. Owners performing the dips should wear gloves and aprons, and dip the pet in a well-ventilated area. The dip should be discarded after use. Owners who are pregnant, diabetic, on antihypertensives, antidepressants or cardiac medications should not perform the dips. In patients with demodex pododermatitis, an amitraz in mineral oil solution consisting of .13%, .5% or 2% has been used topically daily or every three days with the solution being made fresh daily. One formulation that is suggested is lcc amitraz in 29cc mineral oil.
  • Milbemycin: Independent studies by Drs. Reedy and Scott (1992) used milbemycin administered daily at 0.5-1mg/kg BID with a 60 percent cure rate. Milbemycin was used from 30 days to 90 days after a negative skin scraping. A low-dose protocol found a 76 percent cure rate but 75 percent relapsed within the first year of treatment. A high-dose protocol found a 96 percent cure rate with 29 percent relapsing within one year. It is currently unknown how long after a negative skin scraping to continue therapy. I use milbemycin 0.5mg/kg BID until 60 days past a negative scraping. The patient must be heartworm negative before starting therapy. Milbemycin is found to be useful in breeds where ivermectin is contraindicated, such as herding breeds, in dogs with pododemodicosis or excessive skin folds that may be difficult to treat with dips, or where amitraz is contraindicated. Caution should still be used in herding breeds and in any breed using milbemycin. I had a geriatric Yorkshire Terrier that developed head tremors on the 0.5mg/kg BID dose. Reversible head tremors also occurred in a Shetland Sheepdog at 1.7mg/kg/day and two dogs (breed unknown) had reversible ataxia at 3.4mg/kg/day.
  • Ivermectin: The beneficial effect may be from stimulation of GABA (an inhibitory neurotransmitter) or an immunostimulatory effect seen in mice. The dose range from 200ug/kg to 800ug/kg orally daily has been used after first testing negative for heartworm. The daily dose is administered 30 days to 60 days past a negative scraping. Ivermectin should not be used in Collies, Shetland Sheepdogs, Old English Sheepdogs, Australian Shepherds or herding mixes. Some say "if white feet, do not treat." Use ivermectin with caution and always start at the low end of the dose range (200ug/kg/day). Geriatric dogs regardless of the breed may be more sensitive to the side effects of ivermectin. Side effects include lethargy, wheals, ataxia and mydriasis. Adverse effects may not occur until two days to three days after administration. Many veterinarians believe if it occurs within four hours, the side effects may be more severe. In patients on long-term ivermectin, chronic toxicity may develop with prolonged daily use because of the drug's long half-life.


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