Demodex is a species of mite that lives in the hair follicles of a dog’s skin. They’re little cylindrical critters with short, stumpy legs, and they sit next to the hair root within the follicle, grazing peacefully on the sebum secretions.
What do the mites do?
Most of the time, very little! They sit there eating. However, if there are too many of them, then there’s an issue – too many mites in the follicle means that there isn’t room for the hair, which then falls out. They also cause irritation to the follicle (if there are enough of them), resulting in Demodectic Mange – a condition characterised by hair loss WITHOUT itching (unlike the more common Sarcoptic Mange, which is probably the itchiest parasite known). Affected dogs often have erythema (reddened skin) as well, and may develop secondary skin infections (although this is fairly uncommon).
How severe the mange is depends on what areas of the skin are affected. Most cases are localised, meaning they affect only a specific area (typically on the face around the eyes). If, however, it affects the feet it can contribute towards Pododermatitis, an unpleasant condition where the skin between the pads becomes increasingly sore, inflamed and infected.
Occasionally, the mites spread across the whole body, causing generalised Demodicosis – this can result in the dog losing all of it’s coat.
Are they contagious?
Strictly speaking, yes (puppies aren’t born with them, they catch them from their mother in the first day of life). However, all dogs carry Demodex – it’s a normal resident of their skin. For that matter, most humans do as well (generally in our eyelashes), and they don’t cause a problem. Disease only occurs if the mites undergo a population explosion, breeding uncontrollably.
Which dogs are at risk of disease?
In normal, healthy dogs, the population of mites living in their skin is controlled by their immune system. However, in dogs with an immature immune system (affecting certain dogs before the age of 18 months), or a damaged or malfunctioning immune system, the mites can breed to excess unhindered.
Conditions that are known to predispose a dog to mite multiplication include:
- Atopic dermatitis (“Atopy”, a form of severe allergic skin disease).
- Cushing’s disease.
- Dogs on high doses of steroids or other immunosuppressive drugs (those that “calm” or “damp down” the immune system, such as cyclosporine or azathioprine).
- Some hormonal disorders, such as hypothyroidism.
How do you know if they’re causing the problem?
Well, there are of course a wide range of conditions that can cause hair loss in dogs, so proving it’s due to Demodex isn’t as easy as it might sound! The only way to confirm the diagnosis is with a skin scrape – our vets use a scalpel blade to scrape the skin, and try and collect the mites. Unfortunately, Demodex live very deep in the skin, so a “deep skin scrape” is needed, removing all the top layers of the skin (it isn’t uncommon for the site to ooze a tiny amount of blood for a minute or so afterwards – it means that they’ve gone deep enough to guarantee finding all the mites that are present).
The vet (or sometimes one of our qualified nurses) will then examine the scraped up material with the laboratory microscope. Of course, as Demodex are a normal finding in skin, finding just one mite isn’t significant. In most cases of Demodectic Mange, however, the slide is covered in wriggling mites when we look at it – it’s really obvious!
Can it be treated?
As with all parasitic diseases, treatment revolves around killing the mites. However, in most cases there will be an underlying problem that needs to be resolved – a hormone imbalance, or another skin disease, that has allowed them to take over. In this situation, just killing the mites won’t solve the problem – as soon as the treatment is stopped they’ll come back.
We therefore need a two-pronged attack. Firstly, we’ll use powerful insecticides to kill as many of the mites as possible. In most cases, we use a medicated wash containing a drug called amitraz; this is moderately toxic to dogs and people, so make sure they can’t lick at it, and wear gloves! However, it is far more toxic to the mites, and is the most effective way to remove them. Some older dogs, or those with kidney or liver damage, may not tolerate it however, so we can sometimes use an injection containing ivermectin instead – this is less effective, but also much less toxic to most dogs. The exception is collies and other herding dogs, who must never be given ivermectin.
Meanwhile, our vets will start looking for the cause – this usually requires blood tests for hormone imbalances, and sometimes allergy testing too, to find the root cause. Once diagnosed it can be treated, hopefully solving the problem once and for all!
If you think your dog may have Demodex, or any other skin disease, make an appointment to get them checked out by one of our vets.
