Mange is a parasitic skin disease caused by microscopic mites. Two different types of mange mites are significant in dogs. One type lives just under the surface of the skin, while the other type resides deeper in the hair follicles. Although both types of mites share some similar characteristics, there are also important differences. It is important not to confuse the two types of mange because they have different causes, treatments, and prognoses.
Demodectic mange, sometimes just called “demodex,” is the most common form of mange in dogs seen at the Animal Clinic at Thorndale. It is caused by the demodectic mange mite, a parasite which lives deep in the hair follicles of affected dogs. Under the microscope, this mite appears shaped like an alligator or cigar with 8 legs. All dogs (and many humans) have a few of these mites on their skin. As long as the body’s immune system is functioning, these mites cause no harm. We see both localized (small patches of skin affected) and generalized (much of the body affected) forms of Demodex. Young puppies with just a few small patches often outgrow demodex with minimal treatment. The puppy’s immune system develops and takes over. As you might imagine, the generalized form is much more difficult to treat, especially when seen in adult dogs whose immune system should already be well developed.
Contributing Factors
A young dog with demodectic mange usually comes from a litter containing other affected puppies. This is because development of the immune system is under genetic control. Owners of littermates should be put on the alert to watch for it. Because the disease is due to a genetic defect, affected dogs should not be bred. Also, parents of the affected dog should not be bred again. In general, this form of Demodex in juveniles is more manageable than the form found in old dogs. In young dogs, it is often found on localized areas of the skin.
In older dogs, demodex is often a sign of a serious underlying immune disorder. This form is often more difficult to control unless the specific cause of failure in the immune system can be identified and treated.
Prevalence
Demodectic mange is a common parasitic skin disease of dogs. It is primarily seen in dogs less than one year of age. It occasionally appears in senior dogs, which may be a symtpom of another disease process.
Causes/Transmission
Demodectic mange most often occurs when a dog has an immature immune system, allowing the mites to grow rapidly. Consequently, this disease occurs primarily in dogs less than 12-18 months of age. In most cases, the immune system matures as a dog grows. When we see the disease in adult dogs, we can usually make the assumption that the dog has a defective immune system.
Since the mite is found on virtually all dogs, exposure of a normal dog to one with demodectic mange is not dangerous. The dogs own immune system has to be inadequately functioning for the mite to flourish. The other type of mange, called sarcoptic mange, is highly contagious between dogs. Sarcoptic mange is also very itchy.
Clinical Signs
Surprisingly, a dog with demodectic mange does not itch severely, even though it loses hair in patches. Areas of bare skin will be seen. Hair loss usually begins on the face, especially around the eyes. The appearance is often referred to as “moth eaten”.
When there are only a few patches of hair loss, it is termed localized demodectic mange. If the disease spreads to many areas of the skin, it becomes generalized demodectic mange. Generalized demodex is much more difficult to treat.
Diagnosis
Diagnosis is made by a deep skin scraping and hair pluckings that are examined under the microscope. Usually, large numbers of mites are found. The other mange, sarcoptic mange is often difficult to diagnose on skin scrapings because a few mites scattered around can cause perfuse itching. The odds of obtaining mites on a skin scraping is about 30% for sarcoptic mange. When found, the two types of mites appear very different on the microscopic exam.
Treatment
The localized form is usually treated with topical medication. The generalized form requires shampoo therapy and a special dip or oral medication. Shampooing with special cleansing shampoos helps to flush out the hair follicles prior to dipping. Dipping with a chemical call Amitraz is often used in the generalized form. Dipping needs to be done on regular prescribed intervals until at least two successive scrapings for the mites are completely negative. In some cases, it may take over a year to clear the mites. Oral medications, commonly used in heartworm prevention, but at a much higher and more frequent dosing, can also be effective. All medications used to treat demodectic mange have potentially serious side effects. Careful attention to the prescribing directions is necessary to keep both the owner and the dog safe.
For dogs with generalized demodectic mange, secondary skin infections may represent a complicating factor requiring antibiotic therapy. Dogs with skin infections have very red, inflamed skin. This is the source of the term “red mange.”
Because the immune system does not mature until 12-18 months of age, a dog with demodectic mange may have relapses until that age. It is important for retreatment to begin promptly to minimize the possibility of developing uncontrollable problems. Demodectic mange may also occur in very old dogs because function of the immune system often declines with age. Dogs who have immune suppression due to illness or medication are also candidates for demodectic mange.
Prognosis
Treatment of the localized form is generally successful. Treatment of the generalized form is also usually successful. However, if the immune system is defective, neither the mites nor the infection may respond to treatment. Owners need to be aware that in the generalized form, remission may only be partial, or recurrence after an apparent cure is possible.
Transmission to Humans
Canine demodectic mange is not contagious to humans.
Precautions Handling Amitraz Dips to Treat Demodex
The dip commonly used for demodectic mange contains the insecticide amitraz. Its use requires some caution because it is a strong insecticide that can have some side effects to your dog and to you if it is not used properly. Your dog may experience vomiting and sedation for 24-36 hours following each application. If so, those problems will usually be self-limiting. If this occurs, the dip should be diluted with 25% more water the next time it is used. Since each dipping results in the development of tolerance to the dip, your dog is less likely to have side effects with each subsequent treatment. Your dog should be dipped 3 times at 7 day intervals, then examined for the presence of live mites or mite eggs. Further treatment will be determined by the results. If you do the dipping yourself, be sure to wear rubber gloves to prevent getting it on your hands.
- Mix one bottle of amitraz with two gallons of water. Once the bottle is opened, amitraz deteriorates rapidly, even if not diluted. Therefore, unused dip cannot be used later. Wear rubber gloves while handling the dip; wash your hands and arms with soap and water after treatment of your dog. Do not rinse the dip off your dog; allow it to air dry. A hair dryer may be used if the temperature is cool.
- Bathe your dog with the recommended medicated shampoo, then rinse the shampoo. Next, slowly pour the correctly diluted Amitraz dip over the entire body, sponging it in. This should be repeated at 7 day intervals.
- If vomiting or sedation occurs within 24-36 hours after dipping, notify your veterinarian. They may recommend you dilute the dip with 25% more water (2.5 gallons instead of 2 the next time). These side effects should resolve without treatment.
- After the third dipping, we should examine your dog for the presence of live mites or mite eggs. The need for further treatment will be discussed. Some dogs require up to 12-15 dippings before no live mites or eggs are present. We should examine your dog after every third dip.
Administer the dispensed antibiotics according to the label. When the prescription is completed, your dog should be examined to determine if further antibiotic treatment is needed.
At the first sign of recurrence of this disease, we should see your dog again to determine what treatment is needed. This may happen until it is 12-18 months old.