There are a few demodex mites that can cause canine demodecosis. The most common is Demodex canis. Another is Demodex injai. Demodex canis is a normal inhabitant of the skin of healthy dogs and resides in hair follicles. The mite spends its entire life cycle on the dog and it is not considered to be contagious. Dogs become colonized with this mite shortly after birth by direct transmission from the mother to the puppy. Under normal conditions, the presence of low numbers of mites does not cause lesions or disease. However, certain genetic factors and/or impaired immune system function may result in proliferation of mite numbers in hair follicles and cause lesions and hair loss. Clinical signs and lesions associated with a proliferation of mites are variable. These include hair loss (alopecia), red skin (erythema), papules (red bumps), pustules (pimples), hemorrhagic bullae (purple-red blisters), crust, scale, or even nodules. Itch is not typically a feature of canine demodecosis unless there is also secondary bacterial infection affecting the skin.
Canine Demodex Diagnoses
Skin scrapings or hair pluckings are performed when there are lesions indicative of demodecosis. Collected material is evaluated for mites using a microscope. If present, mites are generally easy to recover with this in-hospital diagnostic test. Rarely, biopsies are needed to detect the presence of demodex mites.
We characterize canine demodecosis based upon age of the dog and extent of lesions. Characterization dictates how we treat and monitor patients.
- Juvenile-onset demodecosis is diagnosed when a dog is less than 1 (2 for some breeds) year of age at onset of clinical signs. Most of these dogs develop lesions between 4 and 12 months. In addition to genetic and immunologic factors, we consider the nutritional status, presence of parasites, stress, heat cycles, and the possibility of other underlying diseases that can result in mite proliferation.
- Adult-onset demodecosis is diagnosed when the first clinical signs of the disease occur after the age of 1-2 years. For these dogs, we recommend diagnostic tests to look for underlying conditions such as hyperadrenocorticism (excessive cortisol production by the body), hypothyrodism, other systemic diseases, neoplasia/cancer, current chemotherapy or other immunosuppressive (steroid) therapy.
- Localized demodecosis is diagnosed when there are few lesions limited to a few body sites.
- Generalized demodecosis is diagnosed when there is widespread disease involving several body sites, any number of paws, or a whole body region.
Canine Demodex Treatment
Localized juvenile-onset demodecosis is monitored without additional treatment, as it may resolve with time. All other forms of demodecosis are usually treated. Additional recommendations include spaying and or neutering the pet, deworming if indicated, ensuring a good plane of nutrition, and treating secondary infections. Heartworm testing may be needed depending on the course of treatment. Treatment of demodecosis most commonly uses one of the following in the United States:
- Mitaban (Amitraz) dips are the FDA approved treatment. Dips are performed every 2 weeks in hospital by trained staff and under observation of a veterinarian. Shaving of the hair coat is required unless the coat is short and thin. Your veterinarian will discuss pros, cons and potential side effects of this treatment for your dog. There are two antidotes for this medication, yohimbine and antipamezole.
- Ivermectin 10 mg/ml (1%) liquid is administered once daily by mouth at increasing volumes until a therapeutic dosage is reached. The dosage effective for demodex is much higher than the dosage used to prevent heartworm. Use of ivermectin for the treatment of canine demodecosis is an off-label usage of this product in the dog. Heartworm testing is needed and informed consent is required. The veterinarian should discuss pros/cons and potential side effects of this treatment for your dog. Some breeds cannot be treated with this product. Side effects of this drug when used in an off label fashion such as this, may be dose-dependent or idiosyncratic. The side effects include: depression, anorexia, vomiting, diarrhea, weakness, muscle tremors, ataxia, collapse, dilated pupils, optic neuritis and blindness (usually temporary). There is no specific antidote for ivermectin toxicity. The drug must not be administered to Collie breeds, Collie-crosses, or any dogs of herding breed unless they are confirmed to be unaffected with the MDR-1 genetic mutation via specific genetic testing. Side effects may be seen in other breeds.
The aim of treatment is remission. Remission is achieved when there are 2 consecutive appointments at which deep skin scrapings looking for the presence of mites are completely negative. Treatment is then continued for 4 additional weeks and discontinued. Once in remission, the dog is reevaluated every 3-6 months for deep skin scrapings. If skin scrapings are negative for 1 year after treatment, the dog is considered cured. Relapses occur and are usually recognized in the 3-6 months after treatment is discontinued by the emergence of new lesions on the skin.
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