Mite-induced dermatoses of companion animals (Proceedings)

Canine and Feline Demodicosis

Overview

Demodicosis is potentially severe parasitic skin disease of dogs or cats caused by demodicid mites. Species that occur in the dog and their locations are: Demodex canis (180-210 μm; hair follicle), D. injai (330-370 μm; hair follicle), a recently described short-tailed mite (90-140 μm; skin surface). Feline demodicids include: Demodex cati (approximately 200 μm; hair follicle), D. gatoi (approximately 100 μm; skin surface). Life cycles include adults, eggs, larvae, and nymphs (some divide nymphs into protonymphs and deutonymphs); adults and nymphs have 8 legs and are similar in appearance; larvae have 6 legs; eggs are sometimes amorphous and difficult to recognize, but usually have a demonstrable point (spinose appearance) at one end. The life cycle is completed in approximately 3 weeks.

Signs

Canine demodicosis occurs in two distinct forms and in two different age groups: localized (5 or fewer lesions in one location on the body), generalized (more than 5 lesions in one location or more than one body location); juvenile (small breeds < 12 months, large breeds < 18 months, very large breeds < 2 years); adult ((small breeds > 12 months, large breeds > 18 months, very large breeds > 2 years). Common signs include alopecia, erythema, papular and pustular dermatititis, comedomes, and secondary folliculitis/furunculosis. Most localized cases (90%) resolve in 4- 8 weeks. Dogs with secondary pyoderma may be pruritic; most infested with Demodex alone will not. Adult onset demodicosis can be a severe and even life-threatening disease. It is usually secondary to intercurrent disease (endocrine disorders, immunosuppressive disease, neoplasia). In cats, the head and neck are the principle areas affected (occasionally the trunk and limbs). Lesions include erythema, pustules or papules, alopecia, scaling, ulcers, crusting, comedomes and hyperpigmentation. Erythematous otitis is sometimes observed and may be the only sign. Persian cats are prone to a greasy facial seborrheic form of demodicosis.

Diagnosis

Deep skin scraping, trichogram, biopsy, record of sites and numbers of mites (live/dead, adults vs. immatures) and cytology.

Treatment

Amitraz 0.25% solution (I vial per 2 gallons of water: 250 ppm) administered every two weeks. Clip haircoat before dipping and do not shampoo between dips. Some recommend treating with a follicle flushing shampoo prior to dipping. Treated animals should be allowed to air-dry or should be dried with a blow dryer. In cases of amitraz failure at the approved dose, some recommend increasing the concentration to 500 ppm and treating weekly (this is an off- label use of this product). Signs of amitraz toxicity include lethargy, anorexia, vomiting, diarrhea, hypothermia, pruritis, bradycardia, ataxia, hyperglycemia and excessive salivation (toxicities can be treated with yohimbine 0.1 mg/kg IV; bath before treating). Other treatments include ivermectin (escalating dose: 100 μg/kg for 3 days; 200 μg for 3 days; some remain at 300 μg/kg – others increase the dose every 3 days to 600 μg/kg: can take up to 33 weeks to resolve lesions and eliminate mites). Continue treatment for 1-2 months after two consecutive negative skin scrapings. Some herding breeds such as Collies, Shetland Sheepdogs, Border Collies, Australian Shepherds and Old English Sheepdogs possess mutations in their MDR1 genes, and thus have increased susceptibility to avermectin and milbemycin toxicity. The escalating dose regimen should be discontinued if any of the following signs are noticed: mydriasis, mild salivation, significant changes is behavior, ataxia, or seizure. Dogs can be tested for the presence of the MDR1 mutation by sending a cheek scraping to the College of Veterinary Medicine, Washington State University (www.vetmed.wsu.edu/vpl). Milbemycin oxime can be used in a similar manner, building to a final dose of 1.5 to 2 mg/kg/day. Some say that milbemycin can be used safely in many cases in dogs with the MDR1 mutation. Moxidectin has been used at 0.4 mg/kg per day. The same dosage escalation regimen should be used with moxidectin. A topical product called Advocate (combination of imidacloprid and moxidectin) is marketed in Europe for treatment of Demodex canis infestation. The similar product in the US (Advantage Multi) does not carry the label claim. There is also recent data to suggest that Promeris (metaflumizone/amitraz) may be helpful when used at monthly intervals. Cats can be treated with lime sulfur (weekly dips for 6 weeks with 3.1% solution [4 ounces per gallon of water]). Ivermectin has been used once weekly at 0.3 mg/kg for four consecutive weeks. Ivermectin should be used with caution in cats. Likewise, amitraz has been used in cats (0.0125 to 0.025% solution every 5-7 days for 4 to 6 weeks). Again, this product may induce more reactions in cats than in dogs.

Canine Scabies

Overview

Canine scabies, unlike uncomplicated demodicosis, is an extremely pruritic skin disease. It is caused by Sarcoptes scabei var canis and is easily transmitted between dogs. This variant of Sarcoptes can infest humans transiently causing pruritis and dermatitis, however they are apparently unable to breed in the human dermal environment. Sarcoptes mites are round to oval and white in color. Females (200-400 μm) are larger than males and reside in tunnels in the keratinous layer of the skin. Other life cycle stages include eggs (laid by females in tunnels), one larval and two nymphal stages. The life cycle from egg to adult requires 2-3 weeks. Stages can survive off the host for several days.

Signs

Lesions are seen in dogs most often on the elbows, hocks, ear pinna, and ventral chest, and consist of erythema, alopecia, thickening of the dermis and wrinkling of the skin. Extensive excoriation and secondary bacterial infections are common because of the intense pruritis. Both hyper- and parakeratosis are apparent histologically. Only few mites need be present to cause severe pruritis

Diagnosis

Superficial skin scrapings. However, scrapings are positive only 25-50% of the time. A positive pinnal-pedal reflex is observed about 80% of the time in positive dogs. Because Sarcoptes is extremely susceptible to miticidal therapy, any suspicion of scabies should trigger treatment before considering other differentials such as allergic disease.

Treatment

Selamectin (label dose), Fipronil (labeled as an aid in control when administered monthly), lime sulfur (3.1% solution administered weekly for 4-6 weeks), ivermectin (orally [0.2-0.4 mg/kg every 7 days for 3-4 treatments) or subcutaneously [every 14 days for 2-3 treatments], milbemycin oxime (2 mg/kg every 7 days for 3-5 treatments), amitraz (250 ppm every 2 weeks for 2-3 treatments). A topical product called Advocate (combination of imidacloprid and moxidectin) is marketed in Europe for treatment of Sarcoptes scabei infestation. The similar product in the US (Advantage Multi) does not carry the label claim. There is also recent data to suggest that Promeris (metaflumizone/amitraz) may be helpful when used at monthly intervals. All in contact animals should be treated. All fomites (bedding, combs etc.) should be cleaned and disinfected. Oral corticosteroids may be helpful to control pruritis while mites are dying.

Feline Scabies

Overview

Feline scabies, also known as notoedric mange, is an extremely pruritic skin disease of cats caused by Notoedres cati. This mite is similar to Sarcoptes scabei of dogs and other hosts. As such, its developmental stages, life cycle, and clinical syndrome are similar to Sarcoptes species.

Signs

Affected cats demonstrate severe pruritis, alopecia, crusting and lichenification. Lesions occur most often on the head, face and ears. Occasionally the feet and perineum are involved. Although this mite has zoonotic potential, lesions in humans in contact with infested cats are uncommon.

Diagnosis

Recovery of mites from superficial skin scrapings.

Treatment

None of the following products are label approved for treatment of notoedric mange. Revolution (Selamectin [applied every two weeks for 3 treatments]), lime sulfur (weekly dips for 6-8 weeks), ivermectin (0.2 to 0.3 mg/kg subcutaneously every 2 weeks for 2-3 treatments), amitraz (same regimen used for Demodex gatoi)

Otoacariasis

Overview

Otoacariasis is a disease of the external ear canal of cats and dogs caused by the Psoroptic mite, Otodectes cynotis. Unlike, S. scabei, these mites do not burrow and form tunnels. Mites are not confined in all cases to the ear canal, but may also be found on the head, neck and body. Adult mites are larger and more elongate than S. scabei (females are up to 500 μm long). The life cycle is similar to other parasitic mites (adult, egg, larva, two nymphal stages); development from egg to adult requires about 3 weeks. Otoacariasis is a highly contagious disease that is seen most often in young animals. It is more common in cats than in dogs.

Signs

As mites feed on cells of the external ear canal, they cause inflammation. In serious cases, the ear canal fills with desquamated cells, cerumen, blood, and mites feces. There is little correlation between the amount of ceruminous exudate and evident irritation and pruritis. Some animals are intensely pruritic when only a small amount of exudate is present. Others appear rather normal with more copious exudate. Current evidence suggests that host hypersensitivity to mite saliva may play a role in the pathogenesis of the disease. Human infestations have been reported, but are rare.

Diagnosis

Detection of mites in ceruminous exudates or observation of mites during otoscopic examination.

Treatment

Revolution (Selamectin [approved dog and cat at label dose]), Advantage Multi (Imidacloprid/Moxidectin [approved cat at label dose]), Acarexx (Ivermectin [approved cat at label dose]), Milbemite Otic (Milbemycin oxime [approved cat at label dose]), fipronil (two drops applied in each ear or at base of neck [off label]), ivermectin (0.2 -0.3 mg/kg orally every 7 days for 3 treatments or subcutaneously every 14 days for 2 treatments [off label]) Topical livestock formulations have also been used to treat otoacariasis (off label). Because of the potential presence of mites at other body locations, this author recommends the use of either Revolution or Advantage Multi.

Walking Dandruff Mite (Cheyletiellosis)

Overview

These mites are surface dwellers that infest dogs, cats and rabbits. The specific species are Cheyletiella yasguri, C. blakei, and C. parasitovorax, respectively. Cheyletiellids are large white mites that resemble scales (dandruff). Because the mites crawl within the hair coat, they appear to be dandruff flakes that have come to life. A unique structural feature of cheyletiellids is the presence of claw-like structures on their mouth parts.

Signs

Clinical signs of cheyletiellosis include pruritis, scaling and flaking, and crusted or popular lesions. However, animals can be symptomatic carriers. Cheyletiella spp. are highly contagious and are of zoonotic significance. Since mites can live for up to 10 days off the host, both the infested animal and its environment are sources of human infestation.

Diagnosis

Visualization of mites microscopically in superficial skin scrapings, tape impressions or collections of scales. Scales (dandruff) can be removed with a fine-tooth flea comb and transferred to a microscope slide to which a small amount of mineral oil has been added. The large mites and their characteristic mouthparts are easily visible using 40X magnification.

Treatment

All of the following treatments are off-label. Revolution (Selamectin) is effective at the label dose, administered for 3 consecutive months. Fipronil in both the spray (1-2 pumps per lb every 2 weeks for 3-4 treatments) and spot-on formulations (every 30 days for 3 treatments) are also effective. Lime sulfur (weekly dips for 3-4 weeks), ivermectin (0.2-0.3 mg/kg orally every 7 days for 6 treatments), milbemycin oxime (2 mg/kg every 7 days until mites are no longer observed [can require up to 9 treatments]), and amitraz (weekly dips [250 ppm solution] for 6 to 8 treatments] also have been used. Because this mite lives for long periods off the host, treatment of the environment or consultation with a pest management specialist may be prudent.

Cat Fur Mite

These small mites (the name is Lynxacarus radovskyi) are unique in that they have peculiar hair clasping structures on the ventral aspect of their bodies. Because they attach the hair shafts of cats, they tend to give the haircoat a salt and pepper appearance. These mites are transmitted by direct contact, but are not highly contagious. I am not aware that they present a significant zoonotic risk. Rarely, they cause a papulocrustous rash. Infestations are easily diagnosed by examination of scales or debris in skin scraping or collections from a flea comb. It is likely that Revolution (selamectin) would eliminate these mites at the label dose and regimen. Lime sulfur dips as described above are also effective.

References Available On Request