Hot Literature: Managing canine demodicosis: Practical guidelines for all practitioners

Guidelines for the diagnosis and treatment of canine demodicosis—assembled by an international group of veterinary specialists—are now available to all veterinarians. The purpose was to provide veterinary practitioners with a straightforward description of diagnostics and treatment options in dogs with either localized or generalized demodicosis and to address the differences between juvenile- and adult-onset demodicosis. The recommendations do not take into account availability or label indications of the therapeutics for specific countries or products.

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LOCAL VS. GENERALIZED DISEASE

Characterizing the condition as local or generalized is important because localized forms carry a good prognosis—with most cases spontaneously resolving—while generalized cases pose more treatment challenges and garner the recommendation for neutering to prevent the breeding of these animals. The committee defines localized disease as consisting of no more than four lesions with a maximum diameter of 2.5 cm.

JUVENILE-ONSET VS. ADULT-ONSET DEMODICOSIS

In cases of juvenile demodicosis, Demodex species mites are transmitted to pups from the bitch, but it is thought that a problem with the immune system is necessary to allow these mites to proliferate and cause disease. Anything resulting in debilitation such as malnutrition or endoparasitism could be at the root. In adults, any disease condition that can compromise the immune system may permit the development of demodicosis. However, a cause-and-effect relationship has not been found since many immunocompromised individuals never develop demodicosis.

CLINICAL SIGNS

The forelimbs and face are often affected first, but the lesions can progress to other sites. Mild disease is marked by comedones and scaling, with partial or complete alopecia. Multiple coalescing areas of alopecia and follicular papules indicate moderate disease. More advanced or severe disease is characterized by pustules, furunculosis with scales, crusts, exudation, and ulceration. Draining tracts and nodules can also occur in advanced demodicosis. Secondary pyoderma is a common consequence, and bilateral otitis externa may also occur. In generalized cases, affected dogs may even become lethargic and febrile.

DIAGNOSIS

Identifying Demodex species mites on examination of multiple deep skin scraping samples is the preferred method of diagnosis. Occasionally, mites may be found via trichograms from areas of the body that may be difficult to scrape; skin biopsies are rarely necessary. The guidelines detail the procedures for obtaining diagnostic-quality skin scrape and trichogram samples and examining them for mites.

Whenever possible, perform cytology along with bacterial culture and sensitivity. To optimize therapeutic response, diagnose and treat underlying or predisposing factors.

TREATMENT

For dogs with localized (mild to moderate) disease, weekly administration of topical chlorhexidine or benzoyl peroxide shampoo is recommended. Many dogs' clinical signs will resolve with this treatment alone.

In patients with disease progression or generalized disease, a similar topical therapy given weekly or even twice weekly is recommended. When evidence of secondary bacterial infection is present, perform cytology and bacterial culture and sensitivity, and give the patient appropriate topical or systemic antimicrobial therapy. If the disease persists or progresses, miticidal therapy is necessary.

When treating a patient with demodicosis, you must first consider clinical presentation, local legalities, product availability, and owner finances. Regardless of treatment selection, patients requiring miticidal therapy should be neutered. In fact, the committee states that "ideally, all dogs with demodicosis should be removed from the breeding pool."

Of the mite treatments available, weekly amitraz rinses and daily oral macrocyclic lactones (milbemycin oxime, ivermectin, and moxidectin) have demonstrated efficacy in the treatment of canine demodicosis. Adverse effects are associated with these oral medications in sensitive dogs, especially herding breeds. So it is recommended that the dose be gradually increased until the calculated therapeutic dose is reached. For mild disease, weekly topical (spot-on) moxidectin with imidacloprid can be effective. Examine patients receiving miticidal therapy monthly (three to five skin scraping samples per visit, including the most severe lesions and any new lesions), and change treatment if clinical signs or mite numbers are not improving.

Once all skin scraping results are negative for mites, consider treatment for four to eight more weeks (one month after the second consecutive negative set of scrapings). Treatment should not end with the resolution of clinical signs. Monitor patients that have been treated for generalized demodicosis for recurrence during the first year after remission, and avoid long-term glucocorticoid therapy or any other immunosuppression if possible.

PROGNOSIS

The prognosis is good for dogs with demodicosis, but dogs with persistent underlying immunocompromising conditions may need long-term therapy to maintain clinical remission.

Mueller RS, Bensignor E, Ferrer L, et al. Treatment of demodicosis in dogs: 2011 clinical practice guidelines. Vet Dermatol 2012;23(2):86-98.

A full-text PDF of the guidelines is available at onlinelibrary.wiley.com/doi/10.1111/j.1365-3164.2011.01026.x/pdf

This "Hot Literature" update was provided by Avi Blake, DVM, a freelance technical editor and writer in Eudora, Kan.