Demodex & Mange
Demodex is a skin mite that can parasitize the skin of many animals including dogs and cats. In dogs, the most common species is canis (Demodex canis) that lives in the hair follicles.
How do dogs get Demodex canis?
The most popular theory is that small numbers of mites travel from the mother to newborn puppies shortly after being born. This then means that all dogs have been exposed to Demodex and likewise means that even dogs with normal healthy skin may have Demodex canis somewhere on their body. Of course, it is not feasible to perform skin scraping (the diagnostic test for mites) on every inch of skin of a normal dog to prove that normal dogs can carry Demodex canis. So, until the theory of Demodex canis transfer from mother to puppy is disproven, the consensus is that all dogs, even those with normal healthy skin, carry Demodex canis, albeit in very small numbers.
Are Demodex canis mites contagious to other dogs?
Since all dogs, including those with normal healthy skin, are thought to carry Demodex canis mites, the emphasis is on the individual dog’s ability to control mite numbers with its immune system. Dogs with weakened immune systems appear to be more likely to suffer from developing “mange” from Demodex canis. And there appears to be a hereditary susceptibility to developing mange, so any dog that develops mange should be sterilized so that it cannot breed. A stronger recommendation would be that any dog with positive scrapings for Demodex should not be used for breeding. The dogma is that Demodex canis mites are not contagious to other dogs and that individual susceptibility is the key.
What is demodectic mange?
Mange is the skin disease that results from parasitism by Demodex mites. The most common sign is hair loss (alopecia) not due to self-trauma, followed by redness of the skin (erythema), and scaliness. More severe cases of mange develop darkening of the skin (hyperpigmentation) and secondary bacterial infections, followed by skin ulcers, bleeding, and pus. At this point, most dogs will be lethargic (act ill) and their skin really looks awful.
How is demodectic mange treated?
The standard approved treatment is topical application with an insecticide amitraz (e.g. brand name Mitaban). It comes in small bottles of concentrate that are diluted in a certain amount of water and then applied to the pet’s skin, taking care to avoid the eyes, ears, mouth and broken areas of skin. The solution is irritating and has has strong odor. Many dogs will experience lethargy from the treatment that may last up to 24 hours. It is probably not a good treatment choice for those dogs who are weak, who have serious other systemic illness, or whose skin is severely ulcerated.
Other treatment options:
Another treatment option is the off-label use of milbemycin oxime (Interceptor heartworm prevention). This can be an expensive option and must be used cautiously, if at all, in herding breeds and other breeds who carry the MDR-1 gene mutation. Another related drug, ivermectin, should not be used in herding breeds unless the dog has been tested negative for MDR-1 gene mutation. Dogs with the gene mutation are highly susceptible to side effects and toxicity of this group of antiparasitic drugs. Even in dogs without MDR-1 mutation, all these antiparasite drugs have the potential for side effects.
How long can it take to clear a dog completely of demodectic mange?
By definition, a dog is clear of Demodex canis when multiple skin scrapes are performed at two different examinations in a row, typically one month apart. In the author’s opinion, this is the only useful criteria for declaring an individual is clear of Demodex canis. Multiple skin scrapes of a single visit are not adequate because chance is involved with scrapings: in other words it is possible that mites may be present in other areas of the skin that by chance were not scraped. Stopping therapy means the remaining mites are free to multiply again. The time to achieve two visits both with multiple negative scrapings varies from a few to many months.
Are there other types of Demodex mite species?
Yes, in cats the classic hair follicle mite is called Demodex cati. It shares similarities with Demodex canis in the symptoms it causes. In the Gulf Coast of the USA there is a species of mites in cats called Demodex gatoi. This mite appears to be a surface dwelling mite (lives in skin layers, not the hair follicles) and usually causes intense itchiness (pruritus). Demodex mites with differing microscopic appearance with regard to length and width have been found and reported in dogs. However, some recent studies using DNA analysis suggest “new” species of Demodex mites might be varieties of Demodex canis and not genetically different enough to be considered a true separate species. Regardless, there are cases where Demodex mites may cause unusual types of mange including more pruritus and less alopecia than classic demodectic mange.