Treatment of Demodex and Other Mites: Finally, a Magic Bullet?

Historically, canine demodicosis has been a difficult and frustrating condition to treat. As recently as 2013, the leading veterinary dermatology textbook, Small Animal Dermatology, stated that, despite a good prognosis with appropriate treatment, cure “may take nearly a year”. The need to titrate ivermectin, avoid its use in susceptible breeds, deal with occasional but alarming adverse effects, and repeat scrapings over many months, has made generalized demodicosis a particular challenge for shelters, and created a significant barrier to management and adoption.

Enter the isoxazolines – fluralaner (Bravecto®), afoxolaner (NexGard®) and sarolaner (Simparica®). These products are labelled for control of fleas and ticks in dogs, and fluralaner (Bravecto Topical®) is labelled for fleas and ticks in cats. Some smart veterinarians quickly realized that, like ticks, mites are little critters with 8 legs, and started to try out these products for mite infestation. Preliminary studies and anecdotal reports have been very promising. This is potentially a game changer for demodicosis in dogs in shelter and in communities with limited access to veterinary care, where complex, longterm medication is not feasible.

 

Evidence and Preliminary Recommendations

Studies have compared isoxazolines with imidacloprid + moxidectin (Advantage Multi®, which is currently approved as “an aid in treatment and control” of canine demodicosis.

Fluralaner (Bravecto®; Merck)

• Labelled for canine demodicosis in 9 countries; extra-label in Canada
• A single treatment was clinically as effective as imidacloprid/moxidectin given monthly x 3, and cleared mites more definitively
• Dogs may only need one treatment; treatment can be repeated after 3 months if needed

Afox0laner (NexGard®; Merial)

• Not approved for demodicosis
• Afoxolaner performed significantly better than imidacloprid/moxidectin in one study (both were given at days 0, 14, 28, 56)
• Currently recommended at 1 treatment every 2-4 weeks

Sarolaner (Simparica®; Zoetis)

• Labelled for canine demodicosis in two countries; extra-label in Canada
• Similar improvement when used monthy x 3 treatments compared with imidacloprid/moxidectin weekly x 11-12 weeks
• Recommended as a monthly treatment

 

What about Other Mites? 

Initial studies have shown good results for sarcoptic mange and ear mites in dogs.

 

How About Cats?

Demodicosis in cats is more difficult to confirm because of grooming behaviours – not to mention the difficulty trying to get a cat to hold still for skin scrapings! The option of a therapeutic trial with a long-acting spot-on topical product would be very attractive in this species. A single case report documented the successful use of extra-label oral fluralaner in a single cat – so there’s not nearly enough evidence on cats yet. It will be interesting to see if topical fluralaner, now available for cats in Canada, will prove to be safe and effective for feline demodicosis and/or ear mites.

Watch this space…

 

Cost Comparison

A thesis by Linzey Leinart compared costs of a treatment course for a ~14kg (30lb) dog, using a commercial US-based veterinary pharmacy.  The costs in this study were:

• Bravecto® (1 dose) $36.99
• NexGard® (3 doses) $53.49
• Simparica® (3 doses) $38.49
• A 50mL bottle of Ivomec® (ivermectin) cost $37.95, This bottle would be enough, diluted, to dose almost 70,000 kg of dog. For a shelter treating multiple dogs, ivermectin is much, much cheaper, but there would be no cost advantage for an individual private client if they had to buy a whole bottle.

Canadian prices, and pricing to shelters, were not compared for this blog. Shelters would need to balance the drug price against convenience and safety, labour costs, costs of multiple scrapings, and daily costs of care for a longer duration of treatment using ivermectin.

 

Cautions and Disclaimers

Isoxazolines are currently not labelled for treatment of demodicosis in Canada. These products have several potential side effects (including vomiting, diarrhea and seizures) and should only be used in suitable patients and under veterinary supervision.

There is limited data on the use of isoxazolines for demodicosis, and optimal duration and endpoints are not yet clearly established. Clinical cure of demodicosis occurs 1/2 to 6 months earlier than parasitological cure and up to now, animals have been considered cured after two negative skin scrapings.

There are limitations to the “magic cure”. Many dogs with generalized demodicosis have secondary bacterial and yeast infections, and need additional systemic and/or topical treatment to manage infections and complications. In dogs with adult-onset, generalized demodicosis, an underlying immune-deficiency may be present and recurrences should be assumed to be possible regardless of the product used.

 

References

1. Koch SN. Updates on the Management of Canine Demodicosis. Today’s Veterinary Practice Jan/Feb 2017
2. Leinart LB. Comparison of efficacy, side effects, and cost of isoxasolines and ivermectin against generalized canine demodicosis. Honors thesis, University of Arizona 2017
3. Matricoti I, Maina E. The use of oral fluralaner for the treatment of feline generalised demodicosis: a case report. J Small Anim Prac 2017 58:479-479 doi: 10.1111/jsap.12682. Epub 2017 May 3
4. Peregrine AS. Demodex, Echinococcus and Northern Parasites. Proceedings, Canadian Animal Shelter & Community Medicine Association CPD Day: Parasitology and Infectious Diseases, Toronto, Ontario, November 2017, Toronto, Ontario
5. Waisglass S. A novel approach to the treatment of generalized demodicosis. Canadian Vet March/April 2017 .