Generalized Demodicosis and Other Forms of Demodicosis Requiring Therapy
Once the diagnosis of generalized demodicosis is made, treatment is mandatory both in the juvenile and the adult form. Arbitrarily, generalized demodicosis is clinically characterized by the involvement of either many (at least five) distinct areas or one/several large and diffuse areas. Otodemodicosis and above all pododemodicosis (usually multiple) are also considered severe and must be treated as a generalized form. Without treatment, bacterial cellulitis, which may be fatal, is likely to occur in generalized demodicosis and pododemodicosis
Clipping and cleansing of the lesions are essential at the beginning of the treatment. Benzoyl peroxide shampoos are particularly recommended for their follicular flushing effect.
Amitraz applied topically (concentration: 0.025%) was the first effective topical treatment. Due to insufficient activity and potential secondary effects in both the patient and the person applying the product we no longer use amitraz and prefer systemic macrocyclic lactones.
Milbemycin oxime was the first product administered orally and used to treat generalized demodicosis. It is very effective if the dose is at least 1 mg kg-1 per day (ideally close to 2 mg kg-1). It is licensed in some countries for this use. The rate of clinical and parasitological cure is 60 to 96% but there are 10 to 75% of relapses, particularly at the lowest dosage. We use it but its current price makes it unacceptable for many owners.
Ivermectin is used at the daily dose of 400 to 600 μg kg-1 of the injectable form administered orally. In predisposed breeds in which there is a frequent mutation of the gene mdr 1 (multiple drug resistance1) such as Collies, Shetland Sheepdogs, Border Collies, and Old English Sheep Dogs, a potentially fatal idiosyncrasic reaction is possible and the product should not be used.
Moxidectin is our drug of choice at the moment. We use the injectable form which we give orally at the dose of 400 μg kg-1 daily. Tolerance is good and efficacy seems to be as good as milbemycin oxime if not better: 96% of the patients are cured in 2 to 6 months with a negative parasite evaluation in 2 to 7 months. The recently launched 2.5% spot-on has been relatively ineffective in our hands so far despite its license for generalized demodicosis.
The follow-up of the patients is essential. The treatment should be continued until multiple scrapings are negative, twice one month apart. These must be done in the same body locations (at least five) every month. This procedure is time-consuming; it must be explained to the owner. A control should be done 3 and 12 months after cessation of therapy. Obviously, antibiotic treatment of the associated deep pyoderma is essential. It should be continued beyond its clinical cure and as long as the scrapings show numerous mites. Glucocorticoid therapy, even topically (e.g., auricular formulations) is absolutely contraindicated in generalized demodicosis. In the adult-onset form of the disease, an underlying cause, such as Cushing's disease, must be treated appropriately.
In conclusion, generalized demodicosis is difficult to treat but its cure is achievable with the help of systemic macrocyclic lactones. A thorough follow-up is mandatory.
References are available upon request.