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Overview of Demodicosis (Red Mange) in Dogs
Demodicosis, also known as red mange or “demodex”, is a common skin disease of dogs caused by a microscopic mite called demodex canis. These mites are part of the normal flora of the skin, and are present in small numbers, so the disease is not contagious. In predisposed individuals the mites increase in number causing clinical disease.
Why some dogs develop demodicosis and others don’t is not understood. It is thought to be genetic; affected dogs have an immune system defect that may be inherited, making it difficult to keep the mites under control.
Types of Canine Demodex
There are different forms of this disease: localized and generalized.
This form usually occurs in dogs younger than one year of age. There is no breed or sex predilection. Affected animals are usually healthy and have developed demodicosis as the result of a temporary illness or a stressful event.
The first sign of localized mange might be thinning of the hair around the eyelids, lips, mouth and the front legs – a typical moth-eaten appearance. Prognosis is usually very good, and most animals (90 percent) will recover spontaneously. About 10 percent usually will become generalized.
Generalized demodicosis can begin as a localized case or can present itself as an acute illness. It is frequently categorized according to the age of the dog during the initial onset (juvenile or adult). The main distinction between the two types is the result of differences in predisposing factors and prognosis.
For the generalized form, a genetically inherited predisposition to the disease has been found. For this reason, affected animals should be neutered. Both females and males have the same ability to transmit genetic predisposition to demodicosis. The generalized form of the disease is much more difficult to resolve with therapy and relapses after discontinuation of therapy are common.
What to Watch For
Clinical signs consist of demodicosis consist of numerous patches that appear on the head, legs and trunk. These patches generally develop into large areas of hair loss, and the breakdown of skin leads to the formation of crusty sores.
Diagnosis of Demodex in Dogs
Demodicosis is diagnosed by the presence of symptoms and by performing deep skin scrapings on affected areas. The mites can be seen with the aid of a microscope. The mites are present on all dogs, so alone they do not constitute a diagnosis of mange.
Treatment of Demodex in Dogs
Treatment is necessary when disease is generalized. It includes the treatment of secondary bacterial infections and eradication of the mites. Eradication of the mites can be accomplished by using an amitraz-based dip (Mitaban®) or by using systemic medications (milbemycin and ivermectin). Depending on the breed of your dog, your veterinarian will select the most opportune therapy. Some therapies are not FDA approved (milbemycin and ivermectin) even though they are effective.
It is very important that you closely follow the instructions of your veterinarian to minimize the likelihood of adverse effects. If the dip is used, your dog may need to be clipped to increase penetration and efficacy of this treatment. Adverse effects of the dip include excessive sedation, itchiness, tremors and coma. It is prudent to have your veterinarian dip your dog. After the dip, it is important for you to monitor for excessive sedation. If this occurs your veterinarian should be consulted, as there are medications that can help reverse this adverse effect. Also bathing will remove the residual medication present on the skin and hasten the recovery.
Home Care of Canine Demodex
At home you will have to administer antibiotics for several weeks to treat secondary bacterial infection. This will take four weeks if the infection is superficial, and eight to 10 weeks if the infection is deep.
You will also have to administer oral medication (ivermectin or milbemycin) to kill the mites. The average dog will require medications for a minimum of three months. Compliance is very important not to cause resistance to the medications.
If your veterinarian chooses to use the dip as form of therapy, it is important that your dog does not get wet in between dips to maximize efficacy of the treatment. If, on the other hand, other forms of treatments are used, you may have to bathe your dog regularly with medicated antibacterial shampoos to hasten the recovery and clear the secondary bacterial infections.
If your dog is a collie, Sheltie or Australian shepherd, drugs like ivermectin should never be used because they have the potential of causing life threatening side effects in these breeds (tremors, seizures, coma and death). Other breeds may occasionally have problems with this type of medications but they are usually milder. They include difficulty walking, circling, weakness in the back legs and stumbling.
Information In-Depth on Demodex in Dogs
Demodicosis is a very common skin disease of dogs caused by an abnormal proliferation of demodex mites. Each animal (including humans) harbors its own specific mite species. Demodex mites rarely cause disease in cats, horses, cattle or man and it is not contagious.
The mite causing disease in the dog is called Demodex canis. These mites live in the hair follicles and sebaceous oil glands, feeding on cellular debris. The mites, once off the dog, do not live for very long – only about an hour. The entire life cycle of the demodex mite consists of 25 to 30 days and is completed on the host. Four stages of the life cycle may be evident in skin scrapings. They include spindle-shaped eggs, six-legged larvae, eight-legged nymph, and eight-legged adult.
The pathogenesis of the disease states associated with the proliferation of demodex mites is not completely understood. Most animals harbor very low numbers. In affected animals, the mites proliferate in very large numbers within hair follicles.
Symptoms of Demodex
Juvenile Onset Demodicosis
The juvenile onset version is further classified into localized and generalized. Prognosis and therapy varies for each condition. Several dogs breeds have a higher incidence of demodicosis including Afghan hounds, Boston terrier, boxer, Dalmatian, Chihuahua, English bulldog, Doberman pinscher, American pit bull terrier, German shepherd dog, Old English sheep dog, pug, Shar-Pei, American Staffordshire terrier, collie, and the Great Dane.
Prognosis is good because over 90 percent undergo spontaneous remission in three to eight weeks in spite of therapy. Only 10 percent become generalized.
This form is a much more severe form than the localized form and affected dogs have a genetically inherited predisposition for the disease.
Relapses are common and prognosis is guarded. However, up to 50 percent of these cases may still recover spontaneously without antiparasitic therapy provided that the secondary bacterial infection is addressed, as bacteria may be immunosuppressive.
Both sexes should be neutered, even if the disease cleared spontaneously without treatment.
Adult Onset Demodicosis
Demodicosis is secondary to another disease or immunosuppressive therapy. Conditions commonly associated with adult onset demodicosis include endocrine disease like hypothyroidism and Cushing’s syndrome, metabolic disease and cancer such as lymphoma.
Demodicosis can also be triggered by prolonged steroid therapy. This is the most common cause of adult onset demodicosis.
Prognosis of adult onset demodicosis depends on the nature of the underlying diseases. In some cases (up to 50 percent) no underlying disease is detected at the time of diagnosis, as demodicosis may be the first sign of immunosuppression.
Diagnosis In-depth of Canine Demodex
Diagnosis of demodicosis is based on clinical presentation and positive deep skin scrapings.
The skin should be squeezed and several skin scrapings should be done in the same direction of the hair growth until capillary bleeding is obtained. Hair plucking may be a suitable technique in some dogs in which skin scrapings may not be positive in spite of suggestive clinical signs.
Folliculitis, perifolliculitis and a pyogranulomatous infiltrate are commonly found on histopathology.
Treatment In-depth of Canine Demodex
The mixture (1 vial/2 gallons of water) should be prepared fresh every week and should not be stored and re-used for additional dips. Treatments should be completed in a well ventilated area and gloves must be worn when administering therapy.
Dogs with medium/long hair coat should be clipped. Dogs should be bathed before the dip. A follicular flushing agent is recommended (benzoyl peroxide shampoo) to increase the efficacy of the Mitaban® dip.
Most dogs require six to nine dips to have negative skin scrapings. Therapy should be continued until three consecutive negative scrapings are obtained. Dogs should not be allowed to get wet in-between dips. Dogs should not be sedated the same day of the dip.
Use 25 to 50 percent strength in toy breeds as they are at increased risk for adverse effects. Adverse effects include depression, anorexia, vomiting, itchiness, low body temperature, staggering, slow heart rate, sedation, high blood sugar level and death. Yohimbine can be used as reversal agent for amitraz toxicity. Use label dose or 2 label dose subcutaneously pre- and/or post-dip.
Mite counts should be recorded and animal should be re-scraped in the same sites and new lesions every 30 days. Treatment should be continued at least 30 days beyond last totally negative scraping.
Dogs should be scraped one month after discontinuation of therapy. It is important to remember that besides the eradication of the mites it is vital to address the secondary bacterial skin infections and ensure that no concurrent diseases exist that could impair the ability to respond to treatment.