THE MERCK VETERINARY MANUAL
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Mange in Dogs and Cats

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Sarcoptes scabiei var canis infestation is a highly contagious disease of dogs found worldwide. The mites are fairly host-specific, but animals (including humans) that come in contact with infested dogs can also be affected. Adult mites are 0.3–0.5 mm long, roughly circular in shape, without a distinctive head, and have 4 pairs of short legs. Females are almost twice as large as males. The entire life cycle (17–21 days) is spent on the dog. Females burrow tunnels in the stratum corneum to lay eggs. Sarcoptic mange is readily transmitted between dogs by direct contact; infestation by indirect contact is less frequent but may occur. The incubation period is variable (10 days to 8 wk) and depends on level of exposure, body site, number of mites transmitted, and individuals. Asymptomatic carriers may exist. Intense pruritus is characteristic and is probably due to hypersensitivity to mite products. Primary lesions consist of a papular eruption that, due to self-trauma, develops thick crusts. Secondary bacterial and yeast infections may occur. Typically, lesions start on the ventral abdomen, chest, ears, elbows, and hocks and, if untreated, become generalized. Dogs with chronic, generalized disease develop seborrhea, severe thickening of the skin with fold formation and crust buildup, peripheral lymphadenopathy, and emaciation; dogs so affected may even die. “Scabies incognito” has been described in well-groomed dogs; these dogs, infested with sarcoptic mites, are pruritic, but demonstrating the mites on skin scrapings is difficult because the crusts and scales have been removed by regular bathing. Atypical, including localized, clinical forms that are probably linked to the extensive use of insecticides or acaricides are increasingly observed.

Diagnosis is based on the history of severe pruritus of sudden onset, possible exposure, and involvement of other animals, including humans. Making a definitive diagnosis is sometimes difficult because of negative skin scrapings. Concentration and flotation of several scrapings may increase chances of finding the mites, eggs, or feces. Several extensive superficial scrapings should be done of the ears, elbows, and hocks; nonexcoriated areas should be chosen. Fecal flotation may reveal mites or eggs. A specific and sensitive commercially available ELISA for detection of specific antibodies may be useful. If mites are not found, but the history and clinical presentation are highly suggestive of sarcoptic mange, trial therapy is warranted.

Treatment can be topical or systemic, and should include all dogs in contact. For topical treatment, hair can be clipped, the crusts and dirt removed by soaking with a good antiseborrheic shampoo, and an acaricidal dip applied. Lime-sulfur is highly effective and safe for use in young animals; several dips 7 days apart are recommended. Amitraz is an effective scabicide, although it is not approved everywhere for this use, and there have been some reports of lack of efficacy. It should be applied as a 0.025% solution at 1- or 2-wk intervals for 2–6 wk. It should not be used in Chihuahuas, pregnant or nursing bitches, or puppies <3–4 mo of age. In addition, the owner must observe certain precautions to avoid self-contamination. Fipronil spray was reported to be effective but should be considered an aid in the control rather than a primary therapy.

Systemic treatments of scabies are based on the administration of macrocyclic lactones, some of which are licensed for this purpose. Among them, selamectin is given as a spot-on formulation at 6 mg/kg once or twice at a 1-mo interval. This drug appears to be safe, even in ivermectin-sensitive Collies, and may be used in dogs 6 wk of age or older. In some countries (but not the USA), moxidectin is also registered for the treatment of scabies. It is available as a spot-on formulation in combination with an anti-flea product (imidacloprid) and should be given in 2 doses of 2.5 mg/kg, 4 wk apart. Dogs <7 wk of age and/or weighing <1 kg should not be treated with this spot-on formulation; additionally, oral uptake should be prevented in at-risk breeds. Other endectocides, such as milbemycin oxime and ivermectin, which are not registered for the treatment of sarcoptic mange in dogs, have been reported to be quite effective depending on the dosage and route of administration. The recommended dosage for milbemycin oxime is 2 mg/kg, PO, twice a week for 3–4 wk; potential toxicity should be considered in dogs with MDR1 mutation. Ivermectin (200 μg/kg, PO or SC, 2 treatments 2 wk apart) is very effective and usually curative. Ivermectin at this dosage is contraindicated in Collies and Collie crosses. Idiosyncratic reactions in other breeds may also occur. Additionally, the heartworm status of the dog should be evaluated before treatment with any macrocyclic lactone.

This rare, highly contagious disease of cats and kittens is caused by Notoedres cati, which can opportunistically infest other animals, including humans. The mite and its life cycle are similar to the sarcoptic mite. Pruritus is severe. Crusts and alopecia are seen, particularly on the ears, head, and neck, and can become generalized. Mites can be found quite easily in skin scrapings. Treatment consists of lime-sulfur dips at 7-day intervals. Extra-label use of amitraz is not recommended in cats. Nonapproved but efficient treatments include selamectin (6 mg/kg, spot-on), moxidectin (2.5 mg/kg, spot-on), and ivermectin (200 μg/kg, SC). Sudden death in kittens has been reported with the use of ivermectin.

Otodectes cynotis mites are a common cause of otitis externa (see Otitis Externa) especially in cats but also in dogs. Mites that belong to the family Psoroptidae are usually found in both the vertical and horizontal ear canals, but occasionally are seen on the body. Clinical signs include head shaking, continual ear scratching, and ear droop. Pruritus is variable. Dark brown cerumen accumulation in the ear and suppurative otitis externa with possible perforation of the tympanic membrane may be seen in severe cases. Affected and in-contact animals should receive appropriate parasiticide treatment in the ears and on the whole body for 2–4 wk. Other effective treatments include systemic macrocyclic lactones. Only selamectin and moxidectin (in some countries outside the USA) are approved for treatment of otodectic mange; they are given as spot-on formulations (see Sarcoptic Mange (Scabies)). As a general rule, ear cleansing with an appropriate ceruminolytic agent is indicated with topical therapy and especially with systemic therapy.

Cheyletiella blakei infests cats, C yasguri infests dogs, and C parasitovorax infests rabbits, although cross-infestations are possible. This disease is very contagious, especially in animal communities. Human infestation is frequent. Mite infestations are rare in flea-endemic areas, probably due to the regular use of insecticides. These mites have 4 pairs of legs and prominent hook-like mouthparts. They live on the surface of the epidermis, and their entire life cycle (3 wk) is spent on the host. Female mites can, however, survive for as long as 10 days off the host. Clinical disease is characterized by scaling, a dorsal distribution, and pruritus, which varies from none to severe. Cats can develop dorsal crusting or generalized miliary dermatitis. Asymptomatic carriers may exist. The mites and eggs may not be easy to find, especially in animals that are bathed often. Acetate tape preparations, superficial skin scrapings, and flea combing can be used to make the diagnosis.

Both topical and systemic acaricides are effective against cheyletiellosis, although no drugs are currently licensed for this indication. In addition to treatment of the affected animals, it is necessary to treat all in-contact animals and the environment, including contaminated bedding and grooming material. Topical drugs include lime sulfur, fipronil spot-on and spray, pyrethrins, and amitraz (the latter 2 products are contraindicated in cats). Extra-label systemic drugs include selamectin spot-on, moxidectin spot-on, milbemycin oxime (PO) and ivermectin (SC). Care must be taken to avoid or minimize the risks of adverse reactions as described above (see Sarcoptic Mange (Canine Scabies)). The treatment period depends on the selected drug but must be long enough to eradicate the mites from both the animals and their environment, which can be difficult in animal communities (eg, breeding colonies, kennels). In practice, treatment lasts 6–8 wk and should continue for a few weeks beyond clinical cure until a parasitologic cure is achieved.

This skin disease of dogs occurs when large numbers of Demodex canis mites inhabit hair follicles and sebaceous glands. In small numbers, these mites are part of the normal flora of the skin of dogs and cause no clinical disease. The mites are transmitted from dam to puppies during nursing within the first 72 hr after birth. The mites spend their entire life cycle on the host, and the disease is not considered to be contagious. The pathogenesis of demodicosis is complex and not completely understood; evidence of hereditary predisposition for generalized disease is strong. Immunosuppression, natural or iatrogenic, can precipitate the disease in some cases. Secondary bacterial deep folliculitis, furunculosis, or cellulitis may occur, leading to a guarded prognosis.

Two clinical forms (localized and generalized) of the disease exist. Localized demodicosis occurs in dogs <2 yr old, and most of these cases, especially the nummular forms, are thought to resolve spontaneously. Lesions consist of areas of focal alopecia, erythema and/or hyperpigmentation, and comedones. Pruritus is usually absent or weak. A percentage of these cases, especially the diffuse localized forms, progress to the generalized form. Generalized demodicosis is a severe disease with generalized lesions that are usually aggravated by secondary bacterial infections (pyodemodicosis). Accompanying pododermatitis is common. Dogs can have systemic illness with generalized lymphadenopathy, lethargy, and fever when deep pyoderma, furunculosis, or cellulitis is seen. Diagnosis is not difficult, as deep skin scrapings or hair plucking reveal mites, eggs, and larval forms in high numbers. Whenever generalized demodicosis is diagnosed in an adult dog, medical evaluation to identify an underlying systemic disease should be pursued.

Nummular localized demodicosis can be left untreated. The prognosis for this form is usually good, and spontaneous recovery is frequent. In contrast, treatment is required in cases of diffuse localized demodicosis (which can generalize), generalized demodicosis, pyodemodicosis, and pododemodicosis, for which prognosis is guarded. Hair clipping and body cleansing, especially with benzoyl peroxide shampoo used for its follicular flushing activity, may be required. Whole-body amitraz dips (0.025%) applied every 2 wk remains the only approved treatment for generalized demodicosis in the USA. Higher concentrations (0.05%) and shorter treatment intervals (1 wk) may be more efficient.

Other experimental protocols using daily half-body amitraz dips have been proposed for refractory generalized demodicosis. Among macrocyclic lactones, milbemycin oxime (0.5–1 mg/kg, PO, sid) is approved for generalized demodicosis in some countries. Moxidectin is also registered for the treatment of canine demodicosis in some countries outside the USA; it is available as a spot-on formulation in combination with an anti-flea product (imidacloprid) and should be given at 2.5 mg/kg 2–4 times 4 wk apart. In practice, treatment failures are frequently reported using this approved protocol. Other reportedly successful nonlicensed systemic treatments include moxidectin (400 μg/kg, PO, sid) and ivermectin (300–600 μg/kg, PO, sid). For the latter, different therapeutic protocols have been proposed with a gradually increased dosage and thorough monitoring of patients to detect any potentially toxic effect. Ivermectin is contraindicated in Collies and Collie crosses. However, idiosyncratic toxicity may be seen in any breed. Testing for mutation in the MDR1 allele may be required before initiating therapy. Local and systemic corticosteroids are contra-indicated in any animal diagnosed with demodicosis. Secondary bacterial infections must be treated aggressively with an appropriate antibiotic. Antiparasitic therapy must be continued not only until clinical signs abate but also until at least 2 consecutive negative skin scrapings are obtained at 1-mo intervals. This commonly lasts 4–6 mo. As the sole prophylactic measure, demodectic dogs should not be used for breeding.

Feline demodicosis is an uncommon to rare skin disease caused by at least 2 species of demodectic mites. Demodex cati is thought to be a normal inhabitant of feline skin. It is a follicular mite, similar to but narrower than the canine mite, that can cause either localized or generalized demodicosis. One other species of Demodex (named D gatoi) is shorter, with a broad abdomen, and is found only in the stratum corneum. It causes a contagious, transmissible, superficial demodicosis that is frequently pruritic and can be generalized. In follicular localized demodicosis, there are one or several areas of focal alopecia most commonly on the head and neck. In generalized disease, alopecia, crusting, and potential secondary pyoderma of the whole body are seen. The generalized form is often associated with an underlying immunosuppressive or metabolic disease such as feline leukemia virus infection, feline immunodeficiency virus infection, diabetes mellitus, or neoplasia. In some cases, ceruminous otitis externa is the only clinical sign.

Diagnosis is made by superficial (D gatoi) and deep (D cati) skin scrapings, although mite numbers are often small, especially with D gatoi. Medical evaluation is indicated in cats with generalized disease. Dermatophyte cultures are essential, because dermatophytosis and demodicosis can be concomitant conditions. Prognosis of generalized demodicosis is unpredictable because of its potential relationship with systemic disease. Some cases spontaneously resolve. Weekly lime-sulfur dips (2%) are safe and usually effective; amitraz (0.0125–0.025%) has been used, but is not approved for use in cats and can cause anorexia, depression, and diarrhea. The use of antiparasitic macrocyclic lactones has been reported but their efficacy is unclear.

This common, seasonal noncontagious acariasis is caused by the parasitic larval stage of free-living mites of the family Trombiculidae. It can affect domestic carnivores, other domestic or wild mammals, birds, reptiles, and humans. Two common species found in cats and dogs, Neotrombicula autumnalis and Eutrombicula alfreddugesi, are reported in Europe and in America, respectively. Adult (harvest mites) and nymphs look like small spiders and live on rotting detritus. In temperate areas from summer to fall, dogs and cats can acquire the larvae as parasites when lying on the ground or walking in suitable habitat. In warmer regions, infestation occurs throughout the year. The larvae (0.25 mm long) attach to the host, feed for a few days, and leave when engorged. At that time, they are easily identified as ovoid, 0.7 mm long, orange to red, immobile dots, usually found clustering on the head, ears, feet, or ventrum. Pathogenicity is through traumatic and proteolytic activities. Hypersensitivity reactions are suspected in some animals, as pruritus may vary from none to severe. Lesions include erythema, papules, excoriations, hair loss, and crusts. When present, intense pruritus can persist even after the larvae have left the animal.

Diagnosis is based on history and clinical signs. The infestation is a seasonal threat to free-ranging dogs and cats. Differential diagnoses include other pruritic dermatoses, mainly atopy. Diagnosis is confirmed by careful examination of the affected areas. Microscopic examination of samples obtained from skin scrapings may help to identify the larvae, which have an oval-shaped body that is densely covered with setae, 6 long legs, and curved pedipalps terminating in claws.

Management is difficult. The most useful approach, if feasible, consists of keeping pets away from areas known to harbor large numbers of mites to prevent reinfestation during periods of risk. The application of repellents to prevent infestation has yielded variable results. However, amitraz, fipronil spray, and pyrethroids (in dogs only) could be used, both for prevention and treatment of infested animals. Symptomatic treatment may be required in cases of severe pruritus.

Canine straelensiosis is a rare, noncontagious, sporadic, but potentially emerging parasitic dermatitis caused by the temporary encystment in the epidermis of the parasitic larval stage of Straelensia cynotis. This mite belongs to a family close to the family Trombiculidae. To date, the life cycle is largely unknown and the disease has been reported only in France, Portugal, Spain, and Italy. Transmission occurs mainly in rural and small-sized hunting dogs, probably through contact with contaminated soil, litter, and other terrestrial habitat of foxes. No contagion has been reported to congeners and humans. S cynotis has distinct differences from other trombidioid mites, especially in clinical presentation, histopathologic features, and response to treatment.

Straelensiosis is sudden in onset and may be accompanied by systemic signs such as anorexia and prostration. Lesions are painful, variably pruritic, and either generalized or multifocal, most often affecting the dorsal regions of the head and trunk. The characteristic erythematous papules and nodules resemble small craters. Scaling, pustules, and crusts can be observed.

Differential diagnoses include bacterial folliculitis, sarcoptic mange, and gunshot. Microscopic examination of samples obtained from deep skin scrapings may aid in identification of the larvae (0.7 mm long, 0.45 mm wide), each in a thick-walled cyst. The larvae, which resemble Neotrombicula, are more easily visualized by histopathology.

The prognosis is favorable; a self cure generally occurs after several months if reinfestation is prevented. However, management of clinical signs is difficult. Amitraz may be somewhat effective.

Feline lynxacariasis is a quite common but to date geographically restricted (Australia, Hawaii, Florida, Texas, Brazil) parasitic dermatitis caused by the fur mite Lynxacarus radovskyi, which belongs to the family Listrophoridae. The life cycle remains poorly described, and this species has not been reported from hosts other than cats. Infestation typically occurs by direct contact, but fomites may be important for transmission. Clinical signs include a salt and pepper appearance of the haircoat, variable pruritus, and alopecia. Diagnosis is based on visualization of mites (0.5 mm long) using a magnifying glass or on isolation of any parasitic stage in skin scrapings or acetate tape preparations. Treatment with acaricidal sprays, weekly lime-sulfur dips, and ivermectin (300 μg/kg, SC) are effective. The only case of contagion to humans that has been reported involved a transient rash in an owner with a heavily infested cat.

Last full review/revision July 2011 by Bernard Mignon, DVM, PhD, DEVPC

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