Canine and feline demodicosis (Proceedings)

Canine demodicosis has also been called follicular mange or red mange. Demodex mites are thought to be part of the normal cutaneous flora. They are transmitted from the bitch to the nursing neonates within the first days after birth. Transmission from affected dogs to healthy dogs has only been documented in 1 study. The life cycle of the mite ranges from eggs, to 6 legged larvae to 8 legged nymphs to adults. There are 3 types of mites currently recognized as causing disease in dogs—Demodex canis, Demodex injai and Demodex cornei. Demodex canis is the most commonly recognized of the 3. D. injai is the long bodied demodectic mite and D. cornei is the short, stubby demodectic mite. It is theorized the D. cornei inhabits the stratum corneum whereas the other 2 mites reside in the pilosebaceous units.

Demodex mites in the cat are a short-bodied mite named D. gatoi and a long bodied and more common mite named D. cati. Another species has been reported in the cat, but not yet named. As in dogs, the short bodied mite appears to inhabit the stratum corneum.

Clinical signs of canine demodicosis are basically anything that folliculitis can present as. You can see anything ranging from circular areas of alopecia and scaling to papules and pustules to epidermal collarettes to rupturing folliculitis, furunculosis and multifocal fistulae. In feline cases, the primary presenting sign of D. gatoi is pruritus resulting in self-inflicted alopecia. The alopecia is often symmetrical with the ventral abdomen, flanks and anterior forelimbs common sites. Otitis externa can also be a presenting sign. Additionally, some cats are asymptomatic. This particular mite is also apparently contagious to other cats. On the other hand, D. cati promotes a folliculitis similar to the traditional canine demodicosis. Otitis externa has also been seen as the sole manifestation of this mite.

Diagnosis is obviously via skin scrapings. In the cases of the shorter mites, more superficial skin scrapings will suffice. However, in the more common cases of demodicosis, a deep skin scraping will be necessary to identify the mites. Hair pluckings have also been used to diagnose demodicosis. According to one study, hair plucking may be of value in generalized and complicated demodicosis although negative results cannot rule out demodicosis. Occasionally biopsies and histopathology are necessary to diagnose demodicosis. In the feline cases suspected of having D. gatoi, it may be necessary to do trial therapy for mites as these mites can be difficult to find on skin scraping. It should also be remembered to screen all in contact cats.

Canine demodicosis is traditionally divided into 2 groups—localized and generalized. Localized demodicosis is a bit of an enigma. There is no one single designation and the divisions are blurry. However, the general guidelines are 1-5 lesions with lesions limited to one body area. Rarely, these cases can be limited to otitis externa. This is usually diagnosed in dogs between 3 and 12 mos. of age. Prior to making this diagnosis, you will need to make multiple skin scrapings from seemingly unaffected areas of the body as well. Generalized demodicosis can be further divided into juvenile-onset and adult-onset. The divisions can also be a little grey. Juvenile-onset is general considered to onset between 3 and 18 mos. of age. Adult-onset demodicosis is obviously older. The unfortunate problem is that many people come in with 2-3 year old dogs "that just started having problems". So, some judgment is necessary since many/most of these are probably juvenile-onset. It is important to differentiate as many of the adult-onset cases have underlying issues that need to be worked up. Underlying issues should be investigated in the feline cases as well.

With localized demodicosis, about 90% will spontaneously resolve. The rest may progress to generalized demodicosis. With localized demodicosis, it is best to just monitor and treat any pyoderma that is present. Abstinence from therapy will allow identification for those patients with progressive disease. You can use benzoyl peroxide shampoo or gels for their follicular flushing and antibacterial properties.

When considering therapy, it is very important to remember to look for any possible immunosuppressive issues in the adult onset cases that might be linked to the onset of generalized demodicosis. Additionally, in the juvenile-onset cases, it is important to remember to discuss the heritability of the disease process with the owners. That is, they should let the breeder know that their pup has juvenile-onset demodicosis and they should further take responsibility and have their pup neutered.

Additionally, any secondary bacterial infections will need to be addressed and treated appropriately.

Through the years, many therapies have been used for generalized canine demodicosis. We will discuss the most pertinent at this time. Ronnel (an organophosphate and cholinesterase inhibitor) was an older method that is no longer used due to severe side effects in both the patients and persons applying treatment.

There are currently only 2 label approved methods of treated canine generalized demodicosis—Mitaban and Promeris both of which contain amitraz. Amitraz is a monoamine oxidase inhibitor, and alpha-2 adrenergic agonist and inhibits prostaglandin synthesis. Mitaban is applied topically as a rinse. For long and medium haired dogs, it is best to clip the hair to facilitate the bathing and rinsing process. An antibacterial shampoo (preferably benzoyl peroxide) is recommended to be used prior to using the rinse. The rinsing should be performed by a person with protective clothing in a well-ventilated area as respiratory side effects have been observed in humans. Recommended treatments vary from every other week in the USA at 0.025 % to a stronger concentration weekly in Germany and Australia. This is an EPA regulated insecticide. It seems more frequent stronger dips have a higher success rate, but are off label and more prone to cause side effects. Side effects that may be seen with amitraz therapy are depression, sleepiness, ataxia, polyphagia/polydypsia and vomiting and diarrhea. At higher concentrations, generalized erythema, scaling and an unpleasant odor have been noted. It is important to not use the amitraz rinses with other monoamine oxidase inhibitors or alpha-2 adrenergic agonists. With amitraz rinses, 65% of the juvenile-onset cases achieved clinical and microscopic remission with a relapse rate of 11%.

The spot-on formulation of amitraz (Promeris Duo for dogs) has recently been label approved for monthly use against generalized demodicosis. A recent study was presented using this product every other week on generalized demodicosis cases. Of the juvenile-onset cases treated, 92.3 % has excellent results. In the adult onset cases 45% had excellent results. Excellent results were determined if no mites were identified for 60 days (2 negative scrapings). Side effects that have been noted with this product include pemphigus foliaceus-like pustular drug eruptions, vomiting, diarrhea, transient lethargy and product odor. Longer term remission and cure rates still need to be evaluated.

Systemic macrocyclic lactones such as avermectins (e.g. ivermectin, doramectin) and milbemycins (milbemycin oxime and moxidectin) are broad-spectrum antiparasitic agents produced by the fermentation of various actinomycetes and have been used more recently for the treatment of generalized demodicosis. They bind selectively and with high affinity to glutamate-gated chloride channels results in increased cell permeability of chloride ions and cause neuromuscular blocking resulting in paralysis and death of the parasite. This is also a GABA agonist.

Ivermectin (1%) is the fermentation product of Streptomyces avermitilis and in small animals is licensed only for the prevention of dirofilariasis at a dosage of 6 microgram per kg once monthly. However, it has been used for generalized demodicosis off label at dosages ranging from 300-600 mcg/kg/day PO. Alternatively, it has been used at dosages of 450-600 mcg/kg every other day. Side effects may include lethargy, edematous wheals, ataxia, mydriasis, blindness which may progress to muscle tremors, disorientation, recumbency, stupor and coma. For juvenile and adult onset demodicosis, 68% had clinical and microscopic remission with relapse rates of 18%. You should have each of the clients sign a consent form prior to usage. Many of the herding breeds and rare other dogs may carry a mutation in the MDR1 (ACBC1) gene. This genetic defect results in a lack of P-glycoprotein and clinical sensitivity to high doses of macrocyclic lactones such as ivermectin. There is currently a cheek swab that can be done that tests for this genetic mutation. Further information is available at: http://www.vetmed.wsu.edu/depts-VCPL/. If people opt to not do the genetic testing, then I would strongly recommend to begin at low dosages and very gradually increase to a full dosage of ivermectin (starting at 50mcg/kg to 100, 200, than 300 mcg/kg day). Heartworm status should be checked prior to starting ivermectin as well.

Milbemycin oxime is the fermentation product of Streptomyces hygrosopus aureolacrimosus and in most countries approved only for the use of monthly heartworm and intestinal parasite prevention in dogs at a dosage of 0.5 mg/kg monthly. However, this has also been used off label for the treatment of generalized demodicosis. The most common dosing regimen is 0.5-2 mg/kg/day PO. It has shown a 58% clinical and microscopic remission with relapse rate of 24%. This can be very costly in all but the smallest dogs. This tends to have a wide safety margin, but occasional sensitive patients will develop neurological adverse effects, particularly at higher dosages.

Moxidectin (2.5%) is the active ingredient in Advantage Multi/Advocate. This product also contains imidacloprid and is used for flea, heartworm and some internal parasites in the US. In many other countries, this has been licensed for the treatment of demodicosis in dogs. There are limited studies supporting its efficacy. However, it is also an option, but again is off label.

Doramectin is the final macrocyclic lactone that has successfully been used for therapy of generalized demodicosis. This has been reported to be used weekly at dosages ranging from 200-600 mcg/kg subcutaneously for 5-23 weeks. The same types of adverse reactions with avermectins are possible. So, doramectin should also be started at a low dosage and increased slowly. However, more studies are needed to determine long term efficacy of this product as well.

In feline demodicosis, lime sulfur dips are still the treatment of choice. They can be used at a concentration of 2% every 5-7 days. Again, application of an E-collar may be necessary to inhibit licking and consequent GI signs and oral ulcerations. These dips can be drying, tarnish jewelry and are definitely malodorous. They can also be drying. Trial therapy for D. gatoi can be done with 3 weekly dips.

Amitraz has been used at concentrations of 0.0125-0.025% 2 times per week to every other week. This does work, but can cause sedation, ptyalism and is not recommended.

Ivermectin has also been used at 300 mcg/kg PO daily to every other day, but there is definite potential for toxicity with this.