Demodectic Mange In Your Dog
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Ron Hines DVM PhD.....................................................
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What Causes 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 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. 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 it becomes unavailable online.
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 pet’s sebaceous (oil) glands.
Mange mites are very small. To see them, they must be observed through a microscope. These parasites live primarily in the hair follicles of your pet. A few are also found in the sebaceous glands of the skin adjacent to hair follicles. These are the glands that produce your pet’s hair coat and skin oils. The parasites 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 dogs in low numbers that cause no 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 leaves us asking why some dogs develop demodectic mange and some do not. We know that the juvenile 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.
However, certain pets and certain breeds have problems controlling the mites. In these pets, the number of demodectic mites becomes very large, resulting in skin inflammation (mange). As common as this problem is in dogs, it is unfortunate how little we really understand about its basic cause. It is uncommon for demodectic mange to suddenly occur in mature dogs. When it does occur in older animals, an underlying health issue weakening the pet's immune system, such as Cushing's disease can be the cause. (ref) (spot-on moxidectin and imidacloprid is marketed in the USA as Advantage Multi® aka Advocate Spot On®)
It is 2016 and there have been great advances in our understanding of dog genetics since I wrote this article in 2009. We now know that birth defects in the T-cell immune system of your dog or puppy 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 often notice a small patch of thin or missing hair on the pet’s face, but also occasionally on the leg 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. 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 form of mange.
Generalized Demodectic Mange
The second group of dogs have generalized mange that involves many areas of the 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 pets with demodectic mange itch and scratch. When they do, they usually have a secondary bacterial skin infection that needs treatment. The superficial lymph nodes on these pets are often enlarged. They may run a low fever and appear listless and ill.
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 another chronic heath problem. This can be a hormone imbalance such as an overly active adrenal gland, 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. (ref) Corticosteroid medications, such as prednisone, have been known to trigger Demodex, 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 quite uncommon.
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 infection. 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 and Old English Sheep Dogs to the paw form.
Other medical conditions that cause inflammation of the hair follicles 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 Demodex mites, confirms the diagnosis of demodectic mange. If no mites are found , your veterinarian will tests for these other possible causes of chronic skin disease.
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, the vet will often scrap these lesions with a scalpel blade and a drop of oil to confirm that mites are present. Scotch Tape, pressed against your pet’s skin, and then examined under the microscope may also detect the mites.
If the lesion is confined to a sensitive area of the face, microscopic
examination of the roots of plucked hairs is often sufficient to
find the parasite. When the pet’s ear canals are the only
areas affected, Q-tip swabs can be the sample source.
How Will My Vet 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 - 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 the
pet has been cured. A third negative examination is prudent about
a month later to be sure the cure is permanent.
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.
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, stopping treatment too soon or steroid administration.
Pets weakened by Demodex may need nutritional support, a low stress environment, antibiotics and topical antibacterial and antifungal medications to help 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.
A macrocyclic lactone or avermectin, this is the same compound that is found in many of the once-a-month heartworm preventative tablets. However, it must be used more frequently (every 1-2 days) and at larger doses to kill demodectic mites. The medication 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 like Australian Shepherds, Healers, Old English Sheepdogs, collies and their crosses. But other breeds (ref) 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, pets need to be confirmed heartworm-negative before beginning treatment.
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 (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.
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.
This is a compound similar to ivermectin. Because of that, the same warning given for ivermectin apply to moxidectin. It is 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 this 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))
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 in addition to the medication
used to kill the mites. These antibiotics do not kill demodectic
mites – but they make the chances of curing your pet much
Pets and owners in the same household share the same bacteria. When a pet in your household receives antibiotics, with time, its bacteria may 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. 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 (ref) to minimize the transfer of resistant staphylococcus in hospital settings.
Products That Should Not Be Used
The Jed Clampetts of this World still use the old standby, burnt motor oil. Do not do that because it will injure your pet.
Recent studies suggest that other old-time treatments such as levamazole, 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. If you cannot afford the veterinarian’s fee, talk to the receptionist on the telephone and explain the 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 ?
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 the pets 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 weak. Ivermectin is part of a group of chemicals called avermectins. Those dogs 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. They include the herding dogs: collies, border collies, Australian shepherds, as well as mixed breed dogs that are part 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 gaite), confusion, general weakness, salivation, vomiting, trembling, dilated pupils, loss of vision, and, in severe cases, seizures and coma.
If the medication was applied topically to the pet's body. 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.
Of the mite-destroying medications, Amitraz dips or spot treatments although it too can cause problems in the very young, the debilitated (weak) or when used incorrectly. (ref)
Bravecto ® (fluralaner) an oral flea and tick medication for dogs is said to have been effective in curing demodectic mange. (ref) ; but I have no experience using it to treat mange.
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. I use that product on my Labrador, Maxx, monthly to prevent heartworms and fleas - but never in a specific attempt to cure mange.
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 mechanism.
pets tend to undergo faster and easier cures than older pets. When
pets relapse, it is due to not continuing the treatment long enough
or not using a curative dose rate. 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 your pet. When
dose amounts are increased , they should be increased very gradually
so possible side effects can be 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.
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 will slow or prevent your pet’s recovery from mange.
Can My Other Pets Or People Catch Demodectic Mange ?
Cross-transfer between semi-mature and mature pets appears to be very unlikely in 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 ?
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 for breeding, insist on a contract that
allows you to return the animal if it develops any form of demodicosis.