Demodex

Demodex is a parasite which is part of the normal flora of the skin of dogs but which is also found in cattle, sheep, horses and humans.

In dogs in particular, skin lesions, which can be accompanied by more or less intense itching, appear only when the parasite multiplies exaggeratedly.

Among the factors favoring its proliferation, there are genetics and immunological disorders (stress, malnutrition, immunosuppressive therapy, endoparasites, etc.).

There are two types of Demodex infection: a localized form and a generalized form. The course and prognosis of the infection will vary greatly from one form to another. 

The localized form is common and is found especially in young dogs aged three to six months. It is characterized by some skin areas (less than five) alopecic (absence of hair) with redness and mainly located on the head, especially around the eyes, and on the forelimbs.   

It is usually non-pruritic unless there is a concomitant secondary infection. Healing usually occurs spontaneously.

The generalized form is subdivided into the juvenile form and the adult form. With the latter, the lesions are numerous or extensive and can be found anywhere on the body. The skin can become lichenified (thickened), hyperpigmented and seborrheic. Pustules can also appear with secondary bacterial infections.  

The juvenile form manifests between 3 and 18 months of age. It can resolve by itself but can also persist until adulthood.

The adult form should not be taken lightly. It can hide an underlying (generalized) systemic disease (malignant tumor, immune disease, etc.). Depending on the case, additional tests, such as blood tests for example, can identify it.

It may be more difficult to treat the adult form and relapses may occur. We must therefore be vigilant and watch for the appearance of skin lesions even after the infection seems to have resolved.

Transmission is by direct contact. Demodex is not contagious, except from mother to young during their first days of life.

Some breeds are predisposed and include the Shar-pei, the West Highland White Terrier, the Scottish, the Bulldog, the Boston Terrier, the Great Dane, the Airedale, the Afghan and the Malamute. 

The diagnostic methods are the same for the localized form and the generalized form.

Deep skin scraping often allows us to identify adult Demodex, larvae or eggs. In some cases, only a skin biopsy will allow us to highlight them.

The first step in treatment is to identify, if possible, the primary cause of the infection and treat it.

Affected areas will need to be shaved and cleaned with a bactericidal shampoo and antibiotic therapy may be necessary to treat secondary bacterial infections.

During general demodicosis, safe and effective products must be used to kill the parasite. Treatment should be given up to one month after skin scrapings have confirmed eradication of the parasite.