Ron Hines DVM PhD
What Causes Demodectic Mange?
Mange in your dog can be caused by one of several parasitic mites. The most common two are demodectic mange, the subject of this article, and sarcoptic mange which you can read about here. Cats occasionally develop mange too. Their natural inclination to solitude makes all forms of mange less common in cats. Although cats can develop the same sarcoptic mange that dogs do, the most common form of mange in cats are notoedric mange and a more recently discovered species of demodectic mange that you can read about here .
Demodectic mange in dogs is also called red mange or demodicosis. The parasite responsible for most cases of demodectic mange is Demodex canis – the ones in the illustration on the top of this page. But Demodex injai and D. cornei can also cause similar skin problems in dogs. For reasons unknown, Demodex injai has been found most commonly in terriers. In those breeds it causes an excessively oily, musty coat (seborrheic dermatitis) – particularly along the pet’s spine. Hair loss is minimal. This cousin of D. canis resides mostly in the oil glands (sebaceous glands) found in your dog’s skin. Demodex canis, the more common one, lives primarily in your dog’s hair follicles. Unlike fleas and ticks, all species of demodex spend their entire lifetime on your dog.
How Did My Dog Catch Demodectic Mange?
Most veterinarians believe that Demodex canis is found in the skin of all or most normal dogs. But the number of mites present in their skin is kept low by the dog’s natural immune defenses (its innate immune system). Too low to cause disease. We also believe that puppies probably become contaminated with these mites shortly after birth while they nurse and snuggle with their mother who already harbors a population of mites in her skin. ( read here )
That might leave you asking why some dogs develop demodectic mange hair loss and some don’t. We know that the juvenile (puppy) form of demodectic mange often cures itself after a period of a month or so as the dog’s immune system begins to recognize the mite’s presence and destroy them. This is probably due to your pet’s immune system responding to the parasites and killing them. Age-related immunity is known to neutralize a number of other parasites and this probably occurs with Demodex as well as your pet’s immune system matures and becomes more sophisticated in its abilities. Dogs also differ in their immune system’s ability to locate and destroy demodectic mites. (read here)
Certain dog breeds have difficulty controlling the number of demodectic mange mite in their skin due to their inherited genetic makeup. These are all breeds that were intentionally bred to have abnormally wrinkly skin and skin folds. They include shar-pei, English bull dogs, pit bulls, pugs, bull terriers and staffordshire terriers. Dogs with short hair coat also seem more susceptible to mange than breeds with longer hair coats. The few studies that attempted to explain the underlying reasons these dog breeds have loose wrinkly skin were all focused on the shar-pei breed. Wrinkles are attributed to a genetically-driven excess of hyaluronic acid within their skin. HA is one of the glycosaminoglycans – the same compounds your veterinarian sells as a nutritional aid for arthritis and joint problems. (read here) It is unfortunate how little we veterinarians really understand about the underlying dynamics of demodectic mange in your dog. On a more practical level, when I administer vaccines to these mange-susceptible wrinkly breeds, the hypodermic needle penetrates their skin as if it were butter ( with little or no resistance). I assumed that the skin of these breeds was deficient in collagen, but I have no way to confirm that.
At least some of the genes that account for wrinkly, soft skin reside on chromosome 13 of dogs. They affect the compound, collagen, that gives you and your dog’s skin its normal tone and elasticity. That same chromosome also contains genes that are essential to your pet’s T-cell function that normally destroys demodectic mange mites. In dogs that are at increased risk of demodex or in cases that relapse again and again, those genes are probably defective in some way. ( read here )
It is quite uncommon for demodectic mange to suddenly appear in a mature dog. When it does occur in an older animal, an underlying health issue has probably weakening your pet’s immune defenses. Systemic diseases, such as Cushing’s disease have been known to be the underlying cause of reduced immunity to demodectic mange through the elevated release of cortisol. Diabetes, liver or kidney failure, immunosuppressive tumors or the overuse of corticosteroid medications that suppress your pet’s ability to keep mite numbers under control can be underlying causes as well. So has the generalized debility of heartworms. When a dog over 1.5 years old suddenly develops demodectic mange, a series of tests will be necessary to try to locate its underlying health issue(s). Similar human cases of demodectic mites have occurred in people with suppressed immune systems or those who are forced to take powerful immunosupressive medications. ( read here ) I also received an email from a dog owner whose 12-year-old dog developed demodectic mange shortly after receiving an injection of Apoquel® – another immunosupressive drug.
A medication that often cured those dog is topical moxidectin and imidacloprid. It is marketed in the USA as Advantage Multi® aka Advocate Spot On®). (read here) Check with your veterinarian, read the label and read about breed sensitivities before attempting to apply it to a debilitated animal.
What Signs Will I See If My Dog Has Demodectic Mange?
Dogs commonly come to veterinary hospitals with two forms of demodectic mange:
Localized Demodectic Mange
The first and most common are young dogs that are less than 1.5 years old. Owners or their veterinarian have notice one or two coin-size patches of thin or missing hair on the pet’s face (or occasionally on the legs or trunk). It is rare for these little patches to be inflamed or itchy. These patches are quite distinctive – similar to the one in my illustration. Dog owners often mistake them for ringworm. About Ninety percent of these localized cases resolve in a month or two with or without treatment. But in approximately ten percent, the mites are not eliminated and go on to colonize much of the pet’s skin. Those pets have developed generalized demodectic mange. This unfortunate situation is more likely to occur in dogs whose parents or bloodline (close relatives) previously experienced this same form of mange. Even if cured by your veterinarian, I never suggest that those dogs be bred.
Generalized Demodectic Mange
The second group of dogs have generalized mange that involves many areas of their body. These dogs have sparse or patchy hair coats. Their skin is often overly-pigmented and thickened. These pets have a musty, unhealthy odor. Many have waxy ear infections (ceruminous otitis) due to changes in the bacterial and yeast flora of their skin. ( read here ) Some pets with generalized demodectic mange itch and scratch. When they do, it is usually due to secondary bacterial skin infections that also need treatment. The superficial lymph nodes on these pets are often enlarged. They may also run a low fever and appear listless, ill and depressed. Occasionally, dogs develop demodectic mange that is confined to their feet and paws. When this occurs, the paws become puffy, malodorous and raw due to secondary bacterial infections. These cases can be very stubborn and resistant to treatment. Shar peis, bulldogs and other wrinkly breeds are over-represented in all forms of adult demodectic mange, including the paw form.
How Will My Veterinarian Determine If Demodectic Mange Is My Pet’s Problem?
When your veterinarian is suspicious that your dog might have demodectic mange, your vet will scrap these lesions with a scalpel blade and a drop of mineral oil and place the mixture on a microscope slide to confirm that mites are present. Scotch Tape, pressed against your pet’s skin, and then examined under a microscope can also detect these mites. I have also found demodectic mange mites in stool samples. Those pets ingested the mites while grooming.
If the lesions (hairless or crusty areas) are confined to a sensitive area of the face, microscopic examination of the roots of plucked hairs immersed in lens oil is often sufficient to find the parasites. When the pet’s inner ear flaps are the only areas affected, Q-tip swabs can be the sample source. When secondary skin disease is severe, or when mange has been present for long periods, the mites can be hard to locate. In those cases, skin biopsies usually find them.
Are There Other Problems That Can Be Confused With Demodectic Mange?
Other medical conditions that cause inflammation of the hair follicles and skin can have signs very similar to demodectic mange. They include food allergies, staphylococcal hypersensitivities, skin fungus and yeast infections and long-standing cases of sarcoptic mange. A skin scraping that is positive for an abnormal quantity of demodectic mites, confirms the diagnosis of demodectic mange. If no mites are found , your veterinarian will tests for those other possible causes of chronic skin disease. A number of dogs suffer from more than one of these problems simultaneously.
How Will My Veterinarian And I Know If We Are Making Progress?
Your veterinarian may do periodic skin scrapings every 2-4 weeks during treatment to judge your pet’s rate of recovery. In those examinations, the vet will be looking for immature mites – a sign that the mites are still active and breeding. Large numbers of dead mites are a sign that the treatment is working. A decrease it total mite numbers is also a very good sign.Two consecutive examinations that find no dead or living mites is evidence that your pet is on the way to a cure. A third negative examination is prudent about a month after treatment ceases to be sure the cure was permanent.
What Medications Cure Demodectic Mange?
Be sure to read the section as to when those treatments are usually safe and when they are not.
As I mentioned, young dogs with no more than four isolated small patches of mites generally get better without treatment. However, when the number of patches continue to increase in number or size, it is wise to begin medications.
Rotenone (aka derris root) is a natural product obtained from the roots of several tropical and semitropical plants. Its main use today is in organic farming. Rotenone-containing ointments, such as Goodwinol®, are usually effective when applied to isolated small demodectic mange areas. However, it is impossible to know if it was the medication or the simple passage of time that effected the cure.
Amitraz-containing formulas (Mitaban®) are the only FDA-approved medications for both small patches and more extensive cases of demodectic mange. However the chemical is smelly, messy, hard to apply and prone to side effects in some dogs. Wear gloves and a face shield if you attempt doing it yourself. It is hard to apply correctly without getting a considerable quantity of the milky smelly dip on your cloth and body in the process. Plan to take an immediate bath. Follow the directions on the bottle and remember, if the dip does not penetrate deep enough to reach each mite it will not kill them. Better yet, let your veterinarian’s experienced staff perform these dips. ( read here ) These dips are generally done at veterinary hospitals at 7-14-day intervals. Dips are continued until no living mites are found on skin scrapings. When Amitraz does not cure dogs at the manufacturer’s FDA-suggested dose, veterinarians sometimes resort to increasing the dip concentration or frequency. I no longer use these products because better and safer options are available. Although not a labeled use and while wearing gloves, I have used this product on small isolated patches of demodectic mange as a “rub-in” well massaged into the areas. The dogs all heal. But just like Goodwinol®, one can not say that they wouldn’t have cured themselves with simple “tincture of time”.
Isoxazolines are new group of orally consumed compounds that are very effective in killing fleas and ticks. Read about them here. Every veterinary pharmaceutical company offers their patented isoxazoline with claims that it is more effective than the ones sold by their competitors. But in reality, they are all about the same. A recent publication sponsored by the manufacturer found that one of the newer oral flea/tick medications, ( fluralaner/Bravecto® chewable tablets) also killed demodectic mange mites. However it was not 100% effective when given as a single month’s dose. ( read here ) Another study found afoxolaner/NexGard® about equal in its ability to destroy demodectic mites. ( read here ) That study claimed that NexGard® was superior to the topical moxidectin/imidocloprid product, Advantage Multi® that I mentioned earlier and which I list below as moxidectin. Take all published studies that were paid for by specific manufacturers with a grain of salt – miraculously they always “discover” that their product is more effective than the competition.
Ivermectin is a macrocyclic lactone aka an avermectin. These are the same compounds that are found in many of the once-a-month heartworm preventatives such as Heartgard®. Although it can take a considerable period of time, ivermectin usually cures demodectic mange. However to do so it must be used more frequently and/or at a larger dose than the product labeled for heartworms suggests. Ivermectin works just as well when it is given orally as it does by injection. Because these are “off-label”, non-FDA-approved uses, they need to be administered on the advice and under the care of your local veterinarian. Not because some internet site tells you there is nothing to worry about. I put an image of Heartgard just above. Most veterinarians would purchase a cattle or swine injectable livestock formula of ivermectin to treat demodectic mange and use that product “off label” in your dog because of convenience and economy.
The chief drawback in giving ivermectin and other macrocyclic lactones like moxidectin/Advantage Multi® is that a few dogs are highly sensitive to macrocyclic lactones. Those are dogs that carry a mutant MDR1 gene. These are usually dogs that are all or partly herding breeds such as Australian shepherds, healers, old English sheepdogs and collies. But other breeds sporadically (occasionally) carry this genetic mutation. Dogs with the blue merle coloration often carry some of this genetic background. If this is at all in question regarding your dog, it needs to be checked through a specific blood test . All the macrocyclic lactones in this group quickly kill heartworm larva (microfilaria) circulating in the blood. So your pets need to be confirmed heartworm microfilaria-negative before beginning these treatments or steps need to be taken by your veterinarian to minimize risk before treatment with drugs in this class.
Some dogs that blood tests determine to not have the mutant MDR1 gene still experience side effects from these drugs such as listlessness, skin rash, tremors and unsteady gait – particularly at the high dose levels needed to effectively kill demodectic mange mites. A few dogs experience side effects relating to their eyes. To avoid these problems, I generally test these drugs in your pet at lower level for a week before gradually increasing to a full therapeutic dose. Dogs receiving ivermectin for mange should not receive spinosad-containing medications (eg Comfortis®) during overlapping or closely associated periods.
This is a compound similar to ivermectin. Its chief advantage is that one standard monthly dose of moxidectin persists in the blood stream of most dogs for a full 30 days while ivermectin/Heartgard® rarely persists in your dog’s body longer than 15 days. ( read here & here )The same warnings given for ivermectin apply to moxidectin. Moxidectin is also sold to kill internal and external parasites on livestock. Bayer Pharmaceutical Co. has added moxidectin to their topical flea-control/heartworm preventative product, Advantage Multi® aka Advocate Spot On® . Although it is only approved for treatment of sarcoptic mange in the United States, it is approved for use in treating demodectic mange in Canada and Europe. If you and your veterinarian are faced with a stubborn case of demodectic mange in your canine pet, periodic moxidectin dosing is probably a better choice than ivermectin given at the same frequency.
Antibiotic And Anti Fungal Medications
Dogs with demodectic mange are predisposed to bacterial and yeast skin infections that make mange cures more difficult. When your veterinarian suspects that bacteria or yeast like malassezia have taken advantage of your pet’s unhealthy skin, your vet might decide to put your dog on oral antibiotics or perhaps an antibacterial shampoo containing miconazole/chlorhexidine in addition to the medication used to kill the mites. ( read here ) Those products do not kill demodectic mange mites – but they make the chances of rapidly curing your dog of mange much better and give more immediate relief to suffering dogs.
The bacteria that colonize the skin of dogs with generalized demodicosis often include staphylococcus. There are always a few staph on the surface of your pet’s skin and your skin. But when normal skin defenses and barriers break down, these bacteria get deeper into the pet’s skin than they should. That causes an inflammation called pyoderma .
Dogs, cats, their owners and households always share many of the same bacteria. ( read here ) When a pet in your household receives antibiotics, with time, its bacteria often become resistant to that antibiotic. That is particularly true if the antibiotic is given at too low a dose or for too short a period of time. Staphylococcus is not very particular whether it grows on your pet or on you. If staphylococci later cause problem in you or another family member, the antibiotics that they are already resistant to will no longer work. So wash well with antibacterial soaps when you handle pets receiving antibiotic medications. Do not share products or appliances with pets receiving antibiotics and do what you can to minimize cross-transfer. These are the same precautions that nurses take to minimize the transfer of resistant staphylococcus in hospital settings.
Products That Should Not Be Used
There are still places in this World where the old standby, burnt motor oil, is used to treat mange. When it was used, it was somewhat effective in curing sarcoptic mange if it did not kill the dog first. It never worked for demodectic mange. Never do anything like that – even if Grandpa tells you to. Recent studies suggest that other old-time treatments such as levamasole, ronnel and similar organophosphate insecticides are ineffective in fighting demodectic mange. Although some like chlorpyrifos do kill mites, they are just to toxic to animals for that use. These products are also prone to cause side effects in dogs whose general health has been weakened by mange.
Do not fiddle with any of the accepted mange medications I have mentioned without your veterinarian’s approval and guidance. If you cannot afford the veterinarian’s fee, talk to the receptionist on the telephone and explain your situation. Most veterinarians are compassionate people who will work something out. If not, contact your local humane society.
Can My Other Pets Or People Catch Demodectic Mange From My Dog?
Cross-infection with demodectic mites between semi-mature and mature dogs is thought to be very unlikely. But there have been rare instances where more than one unrelated pet in a household developed demodectic mange. We do not understand why that occurred. Perhaps some strains and species of demodectic mites are more pathogenic than others. Perhaps it was just an unusual coincidence. I would go with the second explanation – particularly if both dogs were of the breeds most commonly affected.
Although dogs, cats and humans all have their own forms of demodex skin problems, they are due to different species of demodectic mites. It takes a trained parasitologist to tell one demodex species from another and mistakes occur. As far as we know, the ones that infest dogs are not a risk to you or your non-dog household members. Occasional reports do pop up in the scientific literature that dispute that. (read here, here & here)