By T. J. Dunn, Jr., DVM
Demodex in the dog is a common infestation of the dog’s skin with tiny, cigar-shaped, eight-legged mites. Also referred to as demodectic mange, the mites reside and feed in the hair follicle and oil glands of the skin.
Demodex is generally less severe than Sarcoptic mites (often called scabies) and in most cases is self-limiting -- that is, the animal is able to arrest the reproduction and growth of the mites and eventually repair the damage they do.
Once eliminated, most dogs do not acquire another infestation; the dog’s immune defenses are primed to eliminate any new demodex mites. However, there are certain dogs that, because of genetic programming, do not produce the specific immune factors that will target the mites for destruction. That specific lack of adequate immune defense against the mites is a hereditary aspect of the disease that can predispose an infested dog to a severe, unresponsive case of demodex.
Many veterinarians believe that all dogs have small numbers of demodex mites residing in the skin and that having a few mites is normal and common. It is when immune related -- or nutritional or environmental -- stresses impact the dog that visible skin lesions from mite infestations become noticeable.
To learn more about Demodicosis, please read the Q&A section below:
Q: Can Demodex mites be inherited?
A: No.The mites are not present on the fetus while the fetus is developing from an embryo in the uterus. However, if the mother has Demodex mites present in/on her skin, the mites can invade the new fetus’ skin immediately after birth. Since many dogs have Demodex mites present in their skin, and never actually develop noticeable skin lesions, the mother may not even be showing any signs of mites and yet transmit mites to the newborn pups. The pups may or may not develop a clinical case of mites.
Q: Why, then, do I keep hearing that Demodex can be inherited?
A: The problem is the wording. The specific antibodies that will defend against infestation of Demodex can be inherited and most dogs have those immune factors and are able to defend against Demodex. But some individuals have inherited a deficiency of those antibodies and just don't have the ability to fend off the mites. So the ability to resist the mites, or not resist, is inherited. The actual mites are not inherited.
Q: So if I have a pup that has Demodex and it is only six weeks old and has never been in contact with any dogs outside our home, the mites must have come from the mother. But the mother has never had Demodex so how could that happen?
A: Your assumption that the mother dog has "never had" Demodex is probably not valid. Demodex mites have been proven to inhabit the hair follicles of many, many dogs, humans and other mammals without causing the host any problems at all. So these mites can be present in normal and healthy individuals (who have inherited the immune factors needed to keep the mites suppressed). So just because you have not experienced a visible skin lesion on your dog does not mean that the dog has no mites present.
Q: How do Demodex mites affect humans?
A: Human demodex cases are rather rare but do occur. The images on the right are of an animal caretaker who became infested in the facial regions with demodex mites. She had been providing the dog with prescribed treatments in the animal hospital. After consulting with a human dermatologist she was eventually able to eliminate the mites but the process entailed numerous topical treatments and also systemic medications. After six months of treatment, all symptoms of the mites disappeared.
Q: If I have a dog that has Demodex, does that mean I should not breed it?
A: If the dog, male or female, has a protracted, difficult-to-cure case of Demodex, that dog should not be bred. If you have a dog that has or had a brief, localized episode of Demodex and has recovered well, then breeding may be considered; but some veterinarians believe that any dog that has displayed skin manifestations of Demodex should be removed from a high quality breeding program.
Q: If a young dog has been diagnosed with Demodex, is it best NOT to spay or neuter the dog until the Demodex has been cleared up?
A: From Dr. David Senter of Englewood, Colorado, a Board Certified Specialist in Veterinary Dermatology ... "Most dermatologists will elect not to treat a dog with generalized demodicosis unless it has been spayed or neutered. The reason for this is simply due to the high likelihood of the affected dog's offspring to develop demodicosis. There is absolutely no benefit to NOT spaying or neutering a dog undergoing treatment. On the other hand, reproductive hormones in female dogs in heat (estrus) or in pregnant dogs can cause worsening of the mites or make it more difficult to control them. However, the presence of male reproductive hormones (un-neutered males) makes no known difference in the ability to control the Demodex mites. On a different note: I do not treat dogs with localized demodicosis (less than six affected spots) because more than 90% of them will resolve on their own. By treating them, you will never know if the patient would have become a generalized case or not.
Q: Is Demodex transmissible to my healthy dog from a dog that is infested?
A: Healthy dogs are quite resistant to infestations and, as mentioned, may already have a number of mites residing harmlessly in the skin. It is best, though, to not allow your dog to have direct physical contact with a dog that has an active case of Demodex ... just to be safe.
Q: What about the dog that suddenly develops Demodex later in life and never had it as a puppy?
A: This is called Adult-onset Demodicosis and is most commonly seen in what are assumed to be healthy dogs but that in reality are actually affected with an underlying pathology or immune compromising disorder. Therefore, whenever a veterinarian is presented with a case of Demodex in an adult dog the doctor is alerted to the possibility that there is a potentially serious underlying disease going on that has compromised the dog's immune integrity. Such afflictions as cancer, Hypothyroidism, Systemic Fungal Disease, adrenal gland diseases and even exposure to prescribed cortisone medications can allow previously innocuous resident mites to reproduce rapidly and cause visible skin disease. Adult-onset demodicosis is not a genetically programmed disorder. These cases can be difficult to cure unless the underlying stressor is resolved successfully.