The Culprit - Demodex Canis

Demodectic Mite

Graphic courtesy MarVistaVet

Demodectic mange, also called "demodicosis," is caused by one of the microscopic mites of the Demodex genus. The most common mite of demodectic mange is Demodex canis. All dogs raised normally by their mothers possess this mite as mites are transferred from mother to pup via cuddling during the first few days of life. Most dogs live in harmony with their mites, never suffering any consequences from being parasitized. If, however, conditions change to upset the natural equilibrium (such as some kind of suppression of the dog's immune system), the Demodex mites may "gain the upper hand." The mites proliferate and can cause skin disease.

Is Demodicosis Contagious?

Unlike sarcoptic mange, demodectic mange is not considered a contagious disease, and isolation of affected dogs is generally not considered necessary. That said, there are some circumstances under which the mites could spread from one dog to another. Classically Demodex mites have been felt to only be transferable from mother to newborn pup. After the pup is a week or so old, it has developed enough immunity so that infection is no longer possible. In other words, after age one week or so, a dog will no longer accept new mites on its body. Recently this idea has been challenged as occasionally multiple unrelated dogs break out with demodicosis in the same household. It is not clear if some species of Demodex are more contagious than others or if some contagion is possible under certain circumstances. Current thinking is that mites can actually be transferred from one dog to another, but as long as the dog is healthy, the mites simply add to the dog's natural mite population, and no skin disease results. In rare circumstances spread of disease is possible if a severe infection is involved. While there are still assorted theories about dog-to-dog transmission of Demodex mites. Mites cannot be transmitted to humans or to cats.

• Mites live inside hair follicles -- a difficult place for miticides (chemicals that kill mites) to reach.
• Mites are normal residents of dog skin; it is only in some individual dogs that mites cause problems.

Localized Infection

Graphic courtesy MarVistaVet

What is Localized Demodectic Mange (also called Localized Demodicosis)?

Demodicosis has three forms: generalized (large areas of skin), pododermatitis (severe foot infection), and localized (only a few spots). The subject shown here is the localized form which is the mildest form. It is usually addressed readily with an isoxazoline flea product, and a single dose is enough to resolve the problem. Most of the time, it resolves with no treatment at all.

Localized demodicosis occurs as isolated, scaly bald patches, usually on the dog's face, creating a polka-dot appearance. Localized demodicosis is considered a common puppyhood ailment and approximately 90% of cases resolve with no treatment of any kind. This is quite a contrast to generalized demodicosis, where large areas of the body surface are involved, so it is important to be able to distinguish localized from generalized disease. It seems like this would be a simple task since localized demodicosis classically involves several round facial bald spots, and generalized demodicosis involves a bald, scaly entire dog; still, reality does not always fit into neat categories in this way. Some guidelines used to distinguish localized demodicosis include:

• Localized disease does not involve more than two body regions. One spot or two on the face and one spot or two on a leg would still qualify as localized even though the spots are not close together.
     
• Localized disease involves no more than four spots total on the dog.

Localized Demodicosis in a Puppy

Puppy with localized demodicosis around one eye. Photo courtesy MarVistaVet

Treatment

Treatment is not necessary for localized demodicosis, but there are treatment options for people who simply cannot feel right if they don't do something. For one thing, flea control products of the isoxazoline class (Simparica®, Nexgard®, Credelio®, and Bravecto®) readily kill Demodex mites, and the simplest treatment is to employ one of these as the patient's flea control product. Any Demodex mites will be killed as a bonus.

Topical antibiotic ointments are usually not needed and may temporarily redden the skin. Applying a topical can also break off some of the local hairs, causing the spot to appear to be enlarging. Neither of these situations makes the condition worse, but it might appear to be getting worse for the reasons mentioned.

As for traditional treatments, Goodwinol ointment, an insecticidal ointment, may be used daily to control localized demodicosis. Antibacterial gels are also used against localized demodicosis and associated skin infections. It is important to note that rubbing a creme or ointment on a demodicosis lesion can cause it to redden, making it appear to get worse. It is also possible that rubbing will break off the weaker hairs at the margin of the lesion, causing the lesion to appear to get bigger. Neither of these situations truly represents an exacerbation of the disease.

Resolution of a localized demodicosis lesion should be at least partially apparent after one month though total resolution can take up to three months.

Approximately 10% of localized demodicosis cases will progress to generalized demodicosis. Enlarged lymph nodes are a bad sign, often foretelling generalized mange. Should the mange progress to the generalized form, more aggressive treatment will likely be needed. 

Can the Pup be Bred Later?

Sometimes the puppy with localized demodicosis was obtained for breeding purposes. The current recommendation is not to treat these puppies so that we can determine if the condition will stay localized and resolve or if it will generalize. If it stays localized and eventually resolves without treatment, the animal is still a candidate for breeding. If the condition generalizes to cover the entire body, the animal should be sterilized. If the condition receives treatment and resolves, it is not known how the disease would have gone in its natural state and will not know whether the pup is carrying the genetic predisposition for generalized demodectic mange. In this case, it is best to be conservative and not take the chance of passing on genetic predisposition for this disease.

Localized demodicosis is almost exclusively a puppyhood disease. When a puppy develops localized demodicosis, the chance of the condition resolving is 90 percent unless there is a family history of demodicosis in related dogs. In this case, the chance of spontaneous resolution drops to 50 percent.

Occasionally an adult dog develops localized demodicosis, but localized demodicosis usually represents nothing more than the stresses and strains that are normal in puppyhood.