Mange in Dogs and Cats - The Merck Veterinary Manual

Mange in Dogs and Cats

Sarcoptic Mange (Canine Scabies)

Notoedric Mange (Feline Scabies)

Otodectic Mange

Cheyletiellosis (Walking Dandruff)

Canine Demodicosis

Feline Demodicosis

Trombiculosis

Sarcoptic Mange (Canine Scabies):

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 legs 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. Untypical clinical forms that are probably linked to the extensive use of insecticides or acaricides may be observed.

Sarcoptic mange, dog

Sarcoptes scabiei var canis

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. Recently, a specific and sensitive ELISA for detection of specific antibodies became commercially available. If mites are not found, but the history and clinical presentation are highly suggestive of sarcoptic mange, trial therapy is warranted. Treatment can be either 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 5 days apart are recommended. Phosmet has been successfully used according to label instructions. Amitraz is an effective scabicide, although it is not approved everywhere for this use, and there have been some reports of lack of efficacy. 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. Among them, only selamectin is approved for this use; it is given as a spot-on formulation at 6 mg/kg twice at a 1-mo interval. This drug appears to be safe, even in ivermectin-sensitive Collies, and is the systemic treatment of choice. Other endectocides, such as moxidectin 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. 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.

Notoedric Mange (Feline Scabies):

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 in skin scrapings. Treatment consists of lime-sulfur dips at 10-day intervals. Nonapproved treatments include amitraz at half the concentration used in dogs, selamectin (4 mg/kg, spot on) and ivermectin (200 µg/kg, SC). Sudden death in kittens has been reported with the use of ivermectin.

Otodectic Mange:

Otodectes cynotis mites are a common cause of otitis externa especially ( Otitis Externa: Introduction) in cats but also in dogs. Mites are usually found deep in the external ear canal, but occasionally are seen on the body. Clinical signs include head shaking, continual ear scratching, and ear droop. Pruritus is variable. Purulent inflammation and discharge of the external ear, and possible perforation of the tympanic membrane may be seen in severe cases. Affected animals should receive appropriate parasiticide treatment in the ears and on the whole body for 2-4 wk.

Cheyletiellosis (Walking Dandruff):

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. 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. Weekly dippings with pyrethrins or lime-sulfur for 6-8 wk are necessary to eradicate the mites. Fipronil and ivermectin are effective, but nonapproved, treatments. The environment should also be treated with a good acaricide, especially in animal communities (eg, breeding colonies, kennels), given the fact that adults may survive off the host for several days or even weeks.

Cheyletiellosis (walking dandruff), rabbit

Cheyletiella blakei

Canine Demodicosis:

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 furunculosis or cellulitis may occur, leading to a guarded prognosis.

Canine demodicosis

Demodex canis

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. Deep skin scrapings 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 always 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 is an approved treatment for generalized demodicosis in the USA. Higher concentrations (0.1%) 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, only milbemycin oxime (0.5-1 mg/kg, PO, sid) is approved for generalized demodicosis in some countries. 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. Local and systemic corticosteroids are contraindicated in any animal diagnosed with demodicosis. Secondary bacterial infections are treated 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. As the sole prophylactic measure, demodectic dogs should not be used for breeding.

Feline Demodicosis:

Two species of mites cause disease in cats. 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. The other species of Demodex (usually named D gatoi ) is shorter, with a broad abdomen, and is found only in the stratum corneum. Feline demodicosis is uncommon. In localized demodicosis, there are one or several areas of focal alopecia on the head and neck. In generalized disease, alopecia, crusting, and secondary pyoderma of the whole body are seen. The generalized form has also been associated with other systemic diseases, especially diabetes mellitus. In some cases, ceruminous otitis externa is the only clinical sign. Pruritus is variable; both species can cause similar disease, but cats infested with D gatoi are more frequently pruritic. Diagnosis is made by deep skin scrapings, although mite numbers are often small. 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 (0.025-0.05%) 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.

Trombiculosis:

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 (Trombicula) 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, lindane, amitraz, fipronil, and pyrethroids could be used, both for prevention and treatment of infested animals. Symptomatic treatment may be required in cases of severe pruritus.