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Demodectic Mange In Your Dog

 

Ron Hines DVM PhD

What Causes Demodectic Mange ?

Mange can be caused by one of a number of parasitic mites. Demodectic mange, caused by Demodectic mites, is one form of mange. I wrote about another type of mange, sarcoptic mange, in another article you can read here. Cats also get mange. The most common form in cats are notoedric mange (ref) and a more recently discovered special form of demodectic mange. Cats can develop sarcoptic mange too, but it rarely occurs in cats. To read about demodectic mange in cats, go to an excellent article in the August 2008 issue of DVM Magazine or see my copy if their's becomes unavailable online 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 cornei can also cause similar problems. Demodex injai has been found most commonly in terriers where it causes an excessively oily, musty coat (seborrheic dermatitis) - particularly along the spine - but little hair loss. This cousin of D. canis resides mostly in the sebaceous (oil) glands found in your pet’s skin. The more common D. canis lives primarily in your pet's hair follicles. All species of demodex spend their entire life on the dog.

How Did My Pet Catch Demodectic Mange ?

Most veterinarians believe that Demodex canis is found in most or all normal dogs in low numbers that are not sufficient to cause disease. We also believe that puppies probably become contaminated with these mites shortly after birth as they nurse and snuggle with their mother who already harbors the mites. However, studies done in 2009 in Italy may challenge that conclusion. (ref)

That might leave you asking why some dogs develop demodectic mange and some do not. We know that the juvenile (puppy) form of demodectic mange often cures itself after a period of a month or so. 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 becomes more sophisticated in its abilities. (ref)

However, certain pets and certain breeds have problems controlling the mite numbers. In these pets, the number of demodectic mites can become very large, resulting in skin inflammation (mange). As common as this problem is in dogs, it is unfortunate how little veterinarians really understand about its basic dynamics. It is very uncommon for demodectic mange to suddenly appear in a mature dogs. When it does occur in an older animal, an underlying health issue has weakening the pet's immune defenses. Systemic diseases, such as Cushing's disease have been known to be the cause of demodectic mange. (ref) (spot-on moxidectin and imidacloprid is marketed in the USA as Advantage Multi® aka Advocate Spot On®) Similar human demodectic mite cases have occurred in people with suppressed immune systems taking powerful medications. (ref)

Understanding how the immune system works has progressed with leaps and bounds since I first wrote this article some time ago. We now know that genetic birth defects in the T-cell immune system of your dog or puppy appear to account for its increased susceptibility to demodectic mange. Shar Pei's (and other wrinkly skinned breeds like bulldogs) have the highest incidence of demodectic mange. The genes that account for wrinkly skin are 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 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. (ref1, ref2)

 

 

What Signs Will I See If My Pet Has Demodectic Mange ?

Dogs commonly come to veterinary hospitals with two forms or stages of demodectic mange.

Localized Demodectic Mange

The first are young dogs that are not yet mature. Owners or their veterinarian often notice one or two small patches of thin or missing hair on the pet’s face (also 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. Some might confuse them for ringworm. Ninety percent of these localized cases will 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 previously experienced this same form of mange. Even if cured by your veterinarian, I never suggest 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).

Some of the pets with generalized demodectic mange itch and scratch. When they do, it is usually due to secondary bacterial skin infections that need treatment. The superficial lymph nodes on these pets are often enlarged. They may run a low fever and appear listless, ill and depressed.

Occasionally, generalized demodectic mange will occur in an older pet that had no previous problems with the mites. Pets that develop demodectic mange later in life generally have a weakened immune system due to an underlying chronic heath problem. That can be a hormone imbalance such as an overly active adrenal gland that I mentioned earlier. But diabetes, liver or kidney failure, an immunosuppressive tumor or the use of medications that suppress your pet’s ability to keep mite numbers under control can be the underlying cause as well. (ref) Corticosteroid medications, such as prednisone, have been known to trigger Demodex in adult dogs, as has the generalized debility of heartworms.

When a dog over two years old suddenly develops demodectic mange, a series of tests will be necessary to try to locate its underlying problem.

The localized, spontaneously-curing, form of demodectic mange does occasionally occur in older dogs. But it is very uncommon. My thoughts are that there was an underlying health it - it just was not discovered through the tests performed.

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 pet might be suffering from demodectic mange, your vet will scrap these lesions with a scalpel blade and a drop of oil and place the mix on a microscope slide to confirm that mites are present. Scotch Tape, pressed against your pet’s skin, and then examined under a microscope may also detect the mites. I have also found them in stool samples, those pets ingested the mites while grooming.

If the lesions are confined to a sensitive area of the face, microscopic examination of the roots of plucked hairs 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 these cases, skin biopsies often locate them.

Are There Other Problems That Can Be Confused With Demodectic Mange ?

Yes

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 fungal 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.

How Will My Vet And I Know If We Are Making Progress ?

Your veterinarian may do periodic skin scrapings every 2-4 weeks during treatment or other microscopic examinations 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, dead mites are a sign that the treatment is working, and a decrease it total mite numbers – also a very good sign.Two examinations that find no dead or living mites is evidence that your pet has been cured. A third negative examination is prudent about a month later to be sure the cure was permanent.

What Are The Treatments That Cure Demodectic Mange

Be sure to read the next section as to when those treatments are safe and when they are not.

Dogs With Localized, Isolated Demodex Lesions :

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 administer medications.

Rotenone-containing creams, like Goodwinol®, and spot treatments with amitraz-containing formulas are often sufficient to eliminate localized demodectic lesions.

Dogs With Generalized Demodectic Mange :

Demodectic mange can be a very stubborn problem. It can take many months of effort to cure it. When medications do not fully cure your pet, failure to eliminate the mites is usually due to generalized poor health that needs attention or stopping treatment too soon or corticosteroid administration. Some of the non-steroidal dermatitis-control medications like Apoquel® might be responsible as well.

Pets weakened by Demodex need nutritional support, a low stress environment, probably antibiotics and topical antibacterial and antifungal medications to help them clear the mites from their skin.

If your pet is slow to respond, your veterinarian my switch medications to see if better results can be obtained with a different medication.

Ivermectin

A macrocyclic lactone or avermectin, (these are the same compound that are found in many of the once-a-month heartworm preventative tablets such as Heartgard®) often cure demodectic mange. However, it must be used more frequently (every 1-2 days ?) and at larger doses to kill demodectic mites. Some of the same medications can be given orally or by injection.

The chief drawback in using ivermectin and other macrocyclic lactones is that a few dogs are highly sensitive to them. These dogs carry a mutant MDR1 gene. These are usually dogs that are all, or part, herding dog breeds such as Australian Shepherds, Healers, Old English Sheepdogs, collies and their crosses. But other breeds are also affected. Dogs with the blue merle coloration often have some of this genetic background. If this is at all in question, avermectin - sensitive dogs can be identified through a blood test.

Since compounds in this group quickly kill heartworm larva in the blood. So pets need to be confirmed heartworm microfilaria-negative before beginning these treatments.

Some dogs that do not have the mutant MDR1 gene still experience side effects such as listlessness, skin rash, tremors and unsteady gait while on this medication at the high dose levels needed to kill the mites. A few have had side effects relating to the eye. To avoid these problems , it is best to test the drug in your pet at low levels for a week or two before graduating to a full therapeutic dose.

Dogs receiving ivermectin for mange should not be receiving spinosad-containing medications (eg Comfortis®) during the same period.

Amitraz (Mitaban®) Dip

This was the “old standby” treatment for demodectic mange. It is still used. The compound is sold as a dip. For it to work, the active ingredient must come in direct contact with the mites. This requires that the pet’s hair coat be clipped and its skin cleaned with shampoos before each application. The smelly dip must be massaged into the pet’s skin while it is partially submerged in the solution (protective ointments are used to protect the pet’s eyes). Specific instructions and cautions are provided with the bottle. These dips are generally done at veterinary hospitals at 7-14-day intervals. I do not suggest you use this product at home.

The solution often ends up on the owner or applicator. It is smelly, stains and can have a number of negative health effects on both the owner and pet. These side effects are more frequent in small breeds, puppies and debilitated pets. Please do not get this material on your body or inhale it.

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 options are available. (ref)

Milbemycin

Often sold as Interceptor® , the advantage of this product over ivermectin is that it generally does not cause the dangerous side effects that can occur in some dogs that receive ivermectin or related compounds. It is sold in tablet form as a heartworm preventative. Using these tablets is an expensive way to treat demodectic mange in dogs that are large. Dogs on milbemycin at the doses needed to kill demodectic mites may still experience side effects such as depression, weakness and, occasionally, seizures.

Milbemycin is also sold in a formula designed to kill ear mites in cats. . Although not designed for use against demodex, it has been effective in treating the mites when they are confined to the area in and surrounding the ear.

Moxidectin

This is a compound similar to ivermectin. Because of that, the same warning given for ivermectin apply to moxidectin. It 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 as of 2009 it had not been approved for treatment of demodectic mange in the United States, it is approved for that use in Canada and Europe. (I mentioned this ref to its use in the treatment of mange earlier in this article. If you and your veterinarian are faced with a stubborn case of demodectic mange in a canine pet, periodic moxidectin dosing is probably a better choice than ivermectin given at the same frequency. That is because moxidectin persists longer in the pet's blood stream than do ivermectin-containing products.(ref))

Antibiotics

Dogs with demodectic mange are predisposed to bacterial skin infections that make mange cures more difficult. When your vet suspects that bacteria have taken advantage of your pet’s unhealthy skin, the vet will put your pet on antibiotics and perhaps antibacterial shampoos and lotions in addition to the medication used to kill the mites. These products do not kill demodectic mites – but they make the chances of curing your pet much better.

The bacteria that colonize the skin of dogs with demodex are often staphylococcus. There are always a few staph on the surface of your pet's skin. But when they get deeper into the pet’s skin than they should, they cause inflammation called pyoderma.

Dogs cats and and owners in the same household always share some of the same bacteria. When a pet in your household receives antibiotics, with time, its bacteria often become resistant to that antibiotic. This is particularly true if the antibiotic is given in too low a dose or for too short a period of time. Staphylococcus are not particular whether they grow in your pet or in you. If these resistant staph later cause problem in you or another family member, the antibiotics that they are resistant to will no longer work. So wash well with antibacterial soaps when you handle pets on these 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. (ref)

Products That Should Not Be Used

There are still places in this World where the old standby, burnt motor oil, is applied to treat mange. When it was used, it was somewhat effective in curing sarcoptic mange - if it did not kill the dog. It never worked for demodectic mange. Never do anything like that because it will injure your pet.

Recent studies suggest that other old-time treatments such as levamasole, ronnel and similar organophosphate insecticides are ineffective in fighting demodectic mange. These products are also prone to cause side effects in pets 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.

Are These Medications Safe For All Dogs With Mange ?

No.

The majority of dogs that develop demodectic mange do just fine on these medications when they are given in the proper dose and at the proper interval.

But that is not always the case. In the case of ivermectin and similar drugs, very young dogs and old or frail dogs may not handle them well (in the standard dose). You see, ivermectin kills mites by disabling the mites nervous system. Most dogs have a gene pair that prevents ivermectin from entering their brain (penetrating the blood brain barrier) and doing damage. (ref) But in some dogs, that pair of genes (MDR1 aka ABCB1 genes) are defective. And in the old, frail or the very young dog, the barrier is also weaker.  Ivermectin is part of a group of chemicals called avermectins. Dogs born with that genetic defect are not only more prone to be sensitive to ivermectin; they tend to be sensitive to the entire family of avermectins which includes many of  the drugs veterinarians use to treat parasites. Certain dog breeds are known for their tendency to have these defective genes. As I mentioned before, they include the herding dogs: collies, border collies, Australian shepherds, as well as mixed breed dogs that are partly those breeds. What I gave you is not a complete list of all of them.

The same sensitivity we sometimes see in those breeds also can occur in any breed or mix if the dose given is too large. As a rule of thumb, those drugs are more apt to cause a problem when they are given orally or by injection and less likely to do so when massaged in small amounts into the skin of affected areas. But that cannot be entirely relied upon. Dogs can be tested to see if they have this defective gene. (ref)

If your dog (or cat - cats are much more sensitive to these drugs!) has a bad reaction to ivermectin or its sister medications the most common signs are ataxia (a drunken gait), confusion, general weakness, salivation, vomiting, trembling, dilated pupils, loss of vision, and, in severe cases, seizures and coma.

If a medication was applied topically to your pet's body and the pet has a reaction, while wearing gloves, wash it off immediately with a warm solution of Dawn dish soap with many rinses. Later, change your clothes. Be sure the pet's head and breathing are supported and get the pet to the vet ASAP.  Dry the dog well with paper towels and keep it warm if it is chilled. (If it has had recent seizures, it may actually have a fever. Also heating pads and lamps are dangerous when a dog is too mentally confused to move away.) There is no antidote for this problem but your vet will give the pet life-sustaining support and, hopefully, it will fully recover.

Amitraz (Mitaban®)dips are unlikely to cause problems when used as spot treatments. But as a whole-body dip they occasionally cause reactions. (ref) I have found them just as effective if only one third to one half of the pet's body is treated at a time.

Bravecto ® (fluralaner) an oral flea and tick medication for dogs was found to be effective in curing demodectic mange. (ref) You can read about that product and others like it here.

Although moxidectin  is in the same drug family as ivermectin, some veterinarians use it, combined with imidacloprid (Advantage Multi® aka aka Advocate Spot On®) to treat mange successfully – even in dogs with the MDR1 aka ABCB1 gene mutation.

In the case of the ivermectin family of medications; when a reaction is mild or minimal, sometimes just lowering the dose is sufficient to continue treatment. Certain medications the dog might be receiving concurrently (spinosad/Comfortis ®, antifungals medications like itraconazole and ketoconazole, certain antibiotics, corticosteroids, Apoquel®/oclacitinib, etc.) can make a bad reaction to the avermectins more likely You can read more on the subject of demodectic mange treatment here, here, here and here .

Can All Dogs Be Cured ?

Almost all dogs can be cured. When the mite infection persists despite accepted treatments, there is an underlying disease that is weakening your pet or your pet has inherited a defect in its defense mechanisms.

Younger pets tend to undergo faster and easier cures than older pets. When pets relapse, it is generally due to not continuing the treatment long enough or not using a curative dose amount. This does not mean that dose amounts should be excessive. High doses do kill mites more effectively – but they also cause more side effects in pets. When dose amounts are increased , they should be increased very gradually so possible side effects can be closely watched for. If your dog is found to be mite-free for 6-12 months, it is unlikely you will ever see the parasite again.

Are There Some General Things I Can Do To Help My Dog Recover ?

Excellent nutrition, low stress and a happy environment are very important to increase the speed and probability of a cure for both demodectic and sarcoptic mange. (ref) Many dogs that develop demodectic mange have had a star-crossed history. This can be insufficient care and nutrition when they were puppies or insufficient care and nutrition of their mother. When the problem is due to breeding dogs that have mange in their blood lines, the problem is more challenging.

The presence of other external or internal parasites can slow or prevent your pet’s recovery from mange.

Can My Other Pets Or People Catch Demodectic Mange ?

Cross-infection between semi-mature and mature pets appears to be very unlikely with demodectic mange. But there have been rare instances where more than one unrelated pet in a family developed demodectic mange. We do not understand why this occurred. Perhaps some strains and species of demodectic mites are more pathogenic than others.

Although cats and humans have their own forms of demodex problems, they are due to different demodectic mites. As far as we know, the ones that infest dogs are not a risk to you or your non-dog pets.

Should I Breed Dogs That Have Experienced Demodectic Mange ?

No.

There is enough evidence that there is a genetic component to demodectic mange to make this a bad idea. Even if your pet recovers spontaneously or after treatment, there were underlying factors that predisposed it to uncontrolled mite proliferation.

If you purchase a puppy of a highly-susceptible breed for breeding, insist on a contract that allows you to return the animal if it develops any form of demodicosis. If you decide that you want to keep the pet anyway, have it spayed or neutered when it is fully mature. (ref)