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Demodectic Mange in Dogs - Causes & Treatment

If you've never heard of the Demodex mite, you're not alone! Someone recently mentioned their dog had been diagnosed with Demodectic Mange (demodicosis) so we decided to investigate. We really should have gone to vet school ...

We enlisted the expertise of veterinarian Dr. Meredith Crowhurst - part of the Pawssum vets on demand team - who kindly shared her wealth of knowledge with us.

What are Demodex Mites?

Demodex mites are minuscule, microscopic creatures that live in the base of hairs (the follicles), within sebaceous glands, and under the skin of animals. 
They have long bodies with eight legs and you can’t see them with the naked eye. The mites naturally live there in small numbers and do not normally cause problems.

Demodex Parasite seen under a dog's skin
from microscope - Photo Credit: iStock
Different species of Demodex mites are specific for different animals. The Demodex species that live on dogs are called Demodex canisDemodex cornei, and Demodex injai

The species that live on cats are called Demodex cati and Demodex gatoi. Humans have their own Demodex mites as well! Animal Demodex mites are not contagious to humans – they stay on their own dog and cat species.

Problems occur when these mites start multiplying excessively... The Demodex mites live on the haired skin of normal, healthy dogs in small numbers. 




Puppies acquire them from their mothers after birth. Sometimes these mites multiply excessively. This is when they cause problems. So what causes the mites to multiply excessively? We don’t fully know. We think that the body’s immune system keeps the mite numbers low in normal dogs and weaknesses in the skin’s defences allow the mites to overgrow.

Things that may weaken the skin’s defences include: 
  • any serious internal disease (such as an underactive thyroid, overactive adrenal gland, cancer, and immune-diseases)
  • intestinal worms
  • poor nutrition
  • immune-lowering medications (like cortisone)
  • pregnancy

Research also suggests an underlying genetic disorder affects the skin of certain breeds. American Staffordshire Terriers and West Highland White Terriers are predisposed to developing young-onset disease.[2] 

What are the symptoms of excess Demodex mites?

We call this overgrowth of Demodex mites, and the symptoms that follow, demodicosis or demodectic mangeSince the mites live in the hair follicles, they cause the hair to fall out, usually in patches. They can also cause dandruff. If they block the hair follicles, they can cause blackheads, which are blocked hair shafts full of oil, dead skin, and bacteria. The Demodex injai mite, which is less common, can cause excess oil production, which causes the skin to become greasy (called seborrhoea). 

Advanced case: Amadeus (Black Terrier); Kirby (Chihuahua Mix)
The mites themselves may or may not cause itchiness. Most do not. But the Demodex mites often cause infection with bacteria or yeast and, when this occurs, the skin becomes red and itchy. 

If the dog scratches the skin, this can exacerbate the infection and cause further skin irritation, creating an ongoing cycle of itching and damage. Pimples, scabs, scratches, puffiness, darkening, and thickening of the skin can develop.

What are the different types of demodicosis?

Demodicosis may affect only a small area of the body or affect a more generalised area. We call it localised when four or less patches of hair loss are involved. The patches of hair loss are generally small and are more often on the face or front legs. Localised demodicosis is usually not harmful and often resolves on its own over 6-8 weeks.


We call the demodicosis generalised when there are five or more patches involved, if it involves the feet, or if it affects a large area of the body.
Generalised demodicosis can be serious. It can cause a serious bacterial infection affecting larger parts of the body. This can make the dog quite unwell, with swelling of the skin, pain, enlarged lymph nodes, tiredness, and a fever.

Although quite uncommon, Demodex injai can also cause disease that only affects the ears.

We also classify the disease as juvenile-onset or adult-onset. It is juvenile-onset if it occurs in dogs up until 18 months of age. Adult-onset disease usually occurs in dogs over four years of age. In a recent study, 59% of adult-onset cases had predisposing risk factors, such as internal disease or being on immune-lowering medications.[2] 


How do we diagnose demodicosis?

We diagnose Demodex mites by doing deep skin scrapes. This is where we put some paraffin oil on the skin, scrape the area with a scalpel blade gently until it bleeds slightly, then put the scraped skin sample on a slide, and look under the microscope. If mites are causing the issue, there will usually be enough for the vet to find them.

To check for bacterial or yeast infection caused by the mites, we press a piece of sticky tape on the skin, place it on a slide, stain it, and look down the microscope. If the ears are involved, we place a sample of ear wax on a slide, stain it, and look down the microscope.

What could demodicosis be confused with?

Other common causes of hair loss in dogs include: 


  • a fungal ringworm infection
  • the scabies mite
  • bacterial and yeast infections
  • hair loss caused by scratching due to allergies (food or environmental), fleas, or infection. 

Sometimes a dog has multiple skin diseases, and this creates a complicated picture. In older adult dogs, we also need to rule out hair loss caused by an underactive thyroid, overactive adrenal gland, or immune-mediated disease. 

What are the treatment options? 

Most cases of juvenile-onset, localised demodicosis resolve spontaneously on their own over a few months. Generalised demodicosis, however, needs to be treated. To kill the mites, common products used include: amitraz, ivermectin, doramectin, and milbemycin oxime. Research shows these are less effective and have more side effects than some of the newer products on the market.[3]

1. Fluralaner (BravectoTM, Merck Animal Health) is a 3-monthly chewable tablet. A 2015 study on 16 dogs showed 100% reduction in mites by 3 months.[1] 

The main side effect is tummy upset. 

In this same study, Moxidectin plus Imidocloprid (AdvocateTM topical liquid, Bayer) used monthly was also highly effective but not 100% by 3 months. Another study showed AdvocateTM used weekly (different to the product-label instructions) can be quite effective.[3] It can cause irritation of the skin. 

2. Afoxolaner (NexgardTM, Nexgard SpectraTM, Merial) is a monthly chew. It reduces Demodex mites and is likely to be highly effective but there is not enough data available yet. The main side effect is a tummy upset.


Storm, blue English Staffy on treatment for Demodex
Treatment is usually required for on average 4-6 months[2], until no mites are seen on consecutive skin scrapes. The skin can appear better as the treatment progresses, but the mites can still be present in excessive numbers. 

If the treatment is stopped before the mite numbers are reduced, then this can cause a relapse. Some dogs require treatment for 15-24 months, a few for longer.[2] 

A dog is considered cured if there are no symptoms 12 months after stopping treatment.


We also need to treat any bacterial or yeast infection. Small areas of infection can be treated with anti-bacterial or anti-yeast creams or shampoos. If a larger area is involved or if the infection is severe, the dog may require antibiotics.


What is the prognosis for a dog with demodicosis? 

The prognosis for juvenile, localised demodicosis is excellent.

The cure rate for generalised demodicosis is about 93%, including juvenile-onset and adult-onset dogs. This number is based on a study that included many dogs treated before Fluralaner and Afoxolaner became available.[2]


With these newer products, the cure rate may be better now. In the study, 11% of dogs relapsed and required repeat treatment. 5.2% required ongoing, continued therapy to prevent relapse. For these dogs, treatment may be easier with the newer chew products. Time will tell.

Buffy's Case

Buffy, a blue American Staffordshire Terrier, is in for her 16-week old puppy vaccination. Over the past couple of weeks, the owners have noticed some patches of hair loss on her head and around her neck. There are a few ‘pimples’ in some areas as well. It is getting worse. Only a few spots are causing her irritation, mostly the areas with pimples. 

I run a blue fluorescent lamp over the areas to look for the characteristic fluorescence of the fungal infection, Ringworm. It doesn’t fluorescence. This doesn’t completely rule out Ringworm because not all fluoresce, but I am more concerned that she has Demodex mites. 

These mites cause patches of hair loss. Staffys are prone and we often see it in puppies. I need to do a ‘deep skin scrape’ to check. This involves placing some paraffin oil on the affected area and scraping the skin gently with a scalpel blade until it bleeds slightly. I place the scraped skin on a slide and look under the microscope. Surely enough, I see Demodex mites wriggling around. 

These mites live in the base of the hairs, in the follicles, and cause the hair to fall out. They sometimes also cause the follicles to become infected. I do another test. I put some clear sticky tape over the red pimply areas, tape it to a slide, stain it with purple dye, and look down the microscope. I am looking for bacteria. 

The areas that are causing her irritation are indeed infected with bacteria as well. The areas affected are small and few and the mites may go away on their own. However, sometimes the mites spread to cover larger areas. If this occurs, Buffy will need to be treated for the Demodex mites. I need to treat her for her bacterial skin infection as well.

written by Dr Meredith Crowhurst, August 2018 (all rights reserved)


About the Writer

Dr Meredith Crowhurst is a Melbourne-based veterinarian from national mobile vet app-based booking service Pawssum.

A Melbourne University graduate with more than a decade of experience, she has extensive consultation and surgical experience and has worked with dogs, cats, rabbits, guinea pigs, rats, mice, birds, and various other animals.

Meredith understands the importance of the human-animal bond. Her aim is to treat pets and their owners with empathy and compassion, delivering the best standard of care.

Previously, Meredith completed a Bachelor of Arts/Bachelor of Science degree and completed her PhD in the biomedical sciences. As well as treating animals, Meredith’s aim is to educate and make medical science knowledge accessible for all.



About Pawssum


Pawssum’s on-demand vets can help with 80% of a pet’s health checks at home. They cover urgent medical check-ups, vaccinations, dental, heart, eye and ear checks, taking blood and lump samples, in-clinic follow up or dog training and behaviourist. There’s even an at-home euthanasia service offering increased comfort and privacy. The Pawssum app also keeps a pet’s complete health records accessible by the pet owner or physician at any time, for continuity of service.

Pawssum vets offer visits out of normal business hours, 7 days a week in all major Australian capital cities. For more information, please visit www.pawssum.com.au or call 1300 34 35 80


References

1. Fourie JJ, Liebenberg JE, Horak IG, et al., Parasit Vectors. (2015) 8:187
2. Bowden DG, Outerbridge CA, Kissel MB, et al., Vet Dermatol. (2018) 29(1):19-e10.
3. Arsenović, M, Pezo, L, Vasić, N et al., Parasitol Res. (2015) 114: 2415.
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