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Spotlight on Canine Adult Generalized Demodicosis

By Dr. Karen Farver, DVM, DACVD | Dermatology

Canine adult generalized demodicosis is a noncontagious parasitic follicular skin disease associated with a genetic or immunologic disorder. It occurs when a dog, older than 18 months of age, has involvement of four or more focal areas of the feet and greater than 2 cm in diameter. This disease allows mites that are normal skin inhabitants to proliferate in the hair follicles and sebaceous glands. It causes alopecia, erythema, comedones, furunculosis, and secondary infections.

Which patients should you evaluate for Demodex?

If they have the following distribution:

  • The face
  • The feet
  • The entire body surface

If they have known detectable underlying disease causing underlying immune suppression or are on immune modulating drugs. 44% percent of dogs have identifiable causes.

Common causes including:

  • Glucocorticoids (even topicals
  • eye drops may affect local
  • periocular demodicosis)
  • Ciclosporin
  • Oclacitinib maleate
  • Chemotherapy
  • Systemic disease (e.g. hyperadrenocorticism, hypothyroidism, neoplasia, malnutrition, parasitism)

Diagnostic analysis

Work up to consider in adult onset demodicosis with no known trigger:

  • Complete blood count
  • Serum biochemical profile
  • Urinalysis
  • Heartworm and fecal tests
  • Lymph node aspirates
  • Thyroid and adrenal testing
  • Abdominal ultrasound
  • Chest radiographs

How to sample?

  • Scrape-Deep till you get capillary bleeding
  • Trichogram from around the eye
  • Sharpei’s — You may need to biopsy
  • Tape acetate preparation, squeeze for 5 seconds first

Update on Treatments

The only labeled treatment for canine demodicosis is Amitraz. Extra-labeled treatments used include doramectin, milbemycin, moxidectin, moxidectin and immidaclopramide, and ivermectin.

Recently Isoxazolines have been shown to be effective for generalized demodicosis. They are labeled for the prevention and treatment of flea and tick infestations in dogs.

This table compares the different Isoxazolines to ivermectin.

Monitoring Treatment

  1. Perform skin scrapings every 4 weeks to monitor response. Continue treatment until 2 consecutive negative skin scrapings are obtained.
  2. If there is minimal reduction in mite numbers and/or substantial eggs, larvae, and nymphs still seen at recheck, reinvestigate for the presence of underlying causes or consider an alternative treatment.
  3. If there is a low mite count, but still significant clinical disease, investigate concurrent skin infections. Secondary bacterial and yeast infections are commonly associated with canine demodicosis. therapy or have a history of multiple antibiotic courses.
  4. Relapses have been reported in 10% to 45% of patients. Monitor patients after treatment is discontinued, every 3 to 6 months the first year. The largest percentage of recurrence of disease occur within the first months after treatment discontinuation.
  5. In patients with refractory demodicosis, treatment may be lifelong.

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