Demodicosis, is the disease caused by the skin mite Demodex canis. This small elongated, cigar shaped skin mite lives in the hair follicles of all dogs and causes no disease in the vast majority of healthy dogs. However, in certain individuals, due to inherent or acquired immune deficiency, the mites can proliferate, unchecked to cause an itchy skin complaint.
All puppies, via their mothers skin, acquire these skin mites. It is in the first couple of days of life the mites transfer, during suckling, from the mothers skin to the muzzle and feet of the puppies, here they colonise in the puppies skin and are normally kept in check by the puppies immune system.
Some dogs have an inherently weak immune system to this skin mite and it is in these individuals that the mites can proliferate and cause disease. Also, adult dogs that do not necessarily have an inherent immune weakness can suffer from this disease if their immunity is weakened by another disease process. For example, severe systemic infection or cancer can weaken the animal's immunity and allow the mites to proliferate and cause disease.
Symptoms of Demodectic mange
Mange is derived from the French word ‘to eat’ and you can appreciate this when you see an animal with mange. The main symptom is scratching and chewing their itchy skin. The skin’s lesions are usually hairless, red patches that tend to start around the face, ears and forepaws but can differ depending on the type/severity of demodectic manage.
Severity of Demodectic Mange
Demodectic mange occurs in two forms; the mild, localised type and the more severe, generalised type.
Localised demodectic manage is recognised by small, itchy, hairless areas on the head, neck and feet. This form normally occurs in younger dogs, around sexual maturity, between 3 and 9 months of age and if normally self-limiting. It usually resolves without treatment.
Generalised demodectic mange affects large areas of skin and tends to be classified by more than five small skin lesions. This type can affect young dogs as well as older animals who are immuno-comprimised by another disease process or immunosuppressive medication.
Onset of Demodectic mange
Demodicosis occurs most commonly in young dogs, around 3-9 months in juvenile onset disease. This age of onset has been linked to puberty and it is thought that the hormonal changes at this age may suppresses the skins defences and enable the mite to proliferate. An adult onset disease is also recognised and this can present at any adult age but is more common in older dogs suffering from another disease process or undergoing medication that suppresses the immune system.
Diagnosis of Demodectic Mange
Demodectic mange is diagnosed by evaluating locations of lesions, age of onset and history of dog e.g. did it’s parents or siblings suffer from the condition and is the dog suffering from a condition which may compromise it’s immune system. Demodectic mange is confirmed by performing a ‘deep skin scrape’ test where a sample of affected skin is scratched with a scalpel blade until bloody ooze is seen – the level of the hair follicle base is reached – this scraped skin material is placed on a microscope slide for examination in the lab. This sample is viewed under microscope and if a significant number of mites are seen then demodectic manage can be confirmed.
Treatment of Demodectic Mange
Treatment is not usually indicated for localised juvenile demodicosis, as the lesions will usually resolve spontaneously as the dog develops. It is thought that the sex hormones may affect the skin’s immunity and enable the mites to cause this disease for the short period of puberty. The decision to treat will depend on the severity of symptoms and will need to evaluated and discussed with your vet.
With generalised demodicosis it is important that investigation for any other disease processes is instigated and that any immunosuppressive medications are stopped. The licensed treatment for canine demodicosis consists of weekly, medicated baths with Aludex (amitraz) for up to eight weeks. Treatment is normally continued until two weeks after skin scrapes show no live mites are present in the skin. Aludex can cause sedation for a period of time after it is applied to dogs, it can also cause skin irritation to the person applying the bath and should be applied in a well ventilated room whilst wearing gloves and avoiding contact with skin and eyes.
For the above reasons Aludex, although effective, does have some undesirable attributes. There are other treatments available under. ‘Spot—on’ preparations such as Pro-meris and Advocate have licenses to treat demodicosis although their effectiveness is debatable.
Rarely resistance of Demodex mites to amitraz is observed; in this instance ivermectin can be used either orally or via regular injections. It should be noted that ivermectin is not licensed for treatment of dogs with this disease and can potentially have it’s own side effects.
Often there are concurrent bacterial skin infections and therefore prolonged courses of antibiotics are usually dispensed along with the medicated baths.
Prevention of Demodectic mange
Prevention of Demodectic mange is achieved by breeding out the genetic suseptibility. This means neutering dogs, male or female, that present with the disease. Furthermore, neutering female dogs that have suffered from juvenile demodicosis will prevent the recurrent disease that can occur in subsequent seasons.
Spread from animal to animal
As discussed earlier, this mite is present in the vast majority of dogs; therefore you do not need to worry about your healthy dog ‘catching’ the disease from an affected animal, it is likely your dog already carries the mites.
Demodectic manage is not infectious to people. A proportion of humans will harbor these mites in their own hair follicles, often their eyebrows, but the mites are not caught from diseased dogs and do not cause disease in humans.