Canine demodicosis is a noncontagious parasitic skin disease caused by an overpopulation of the host-specific follicular mites of the genus Demodex. Most cases of canine demodicosis are caused by Demodex canis, although two other species of demodicid mites are reported.
Canine demodicosis is a noncontagious parasitic skin disease caused by an overpopulation of the host-specific follicular mites of the genus Demodex. Most cases of canine demodicosis are caused by Demodex canis, although two other species of demodicid mites are reported. Localized demodicosis is a common mild and benign self-limiting disease. Generalized demodicosis, in contrast, is a serious and potentially life-threatening disease. Most cases of generalized demodicosis are juvenile in onset and develop in dogs less than 1 year of age. Interestingly, yet there is no universally agreed to definition of ‘generalized', or for the term ‘adult onset ' (as opposed to juvenile). For the purposes of these notes, ‘adult onset' will be defined as any case diagnosed in a dog at over 2 years of age, and ‘generalized' will follow the suggestion of Mueller: …involvement of an entire body region, more than 5 focal areas, and/or paw involvement'.
Most cases of demodicosis are due to Demodex canis, although cases caused by D injai (a large-bodied Demodex species which lives in the hair follicle and the sebaceous glands) and an unnamed short-bodied Demodex species (which lives in the stratum corneum) have been reported.
A genetically preprogrammed immunologic defect probably is responsible for the juvenile onset, generalized demodicosis. Adult onset demodicosis has been reported to be caused by immunosuppressive treatment for neoplasias or auto-immune disorders, or be associated with diseases altering the immune response such as hypothyroidism, hyperadrenocorticism, leishmaniasis, and neoplasias. In the author's practice the most common underlying cause is the long-term use of systemic corticosteroids – these may be at relatively low doses. Perhaps 25% of the dogs have no demonstrable underlying disease.
Diagnosis is by demonstration of the mite on deep skin scraping in a dog fulfilling the lesional and age requirements noted above. The author prefers to use a medical grade spatula (Fisherbrand* Microspatula with Flat-Ended Blade, catalogue number 21-401-20, Fisher Scientific; http://www.fisherscientific.com), as this blade is just sharp enough to scrape deep enough to the first level of capillaries (and hence deep enough to be at the follicular depth of the mites). Dogs which have very thick skin (especially on the feet) due to chronic inflammatory skin disease associated with furunculosis may need to be biopsied in order to demonstrate the mites.
For adult onset generalized demodicosis, the owner should be informed of the potential of an underlying disease, and the clinician should perform diagnostic tests searching for such an etiology. Minimum data base should include a complete blood count and biochemical profile, but depending upon the presentation of the dog (as well as the willingness of the owner to spend money) other tests such as abdominal ultrasound, thoracic radiographs, thyroid hormone panel (T4, free T4, TSH level) and ACTH stimulation test could be performed. If an underlying disease is found, the disease should be treated, as well as proceeding with appropriate miticidal treatment.
It is important to realize that most if not all dogs with demodicosis will have a secondary pyoderma. This is usually caused by Staphylococcus intermedius, but if there is concurrent imunosuppression (for example, from exogenous corticosteroids) other bacteria may be contributing to the pyoderma. The author usually uses cephalexin at 30 mg/kg q12h (for superficial pyoderma) or q8h (for deep pyoderma). Other antibiotics which can be used are enrofloxacin 5-10 mg/kg q24 h, lincomycin 20mg/kg q12h, amoxicillin-clavulanate 13.75 mg/kg q12h or marbofloxacin 3-5 mg/kg q 24 h. Antibiotic treatment is usually continued for a minimum of 2 months.
There are several different miticidal treatments that are available to treat generalized demodicosis. In all cases the dog's mite population should be monitored by means of a deep skin scraping once monthly. The owners should be instructed to continue treatment until the dog has 2 consecutive negative scraping sessions. ‘Negative' in this instance means NO live or dead adult mites, nymphs, larva, or eggs. Thus, minimum miticidal treatment time will be 2 months. In actuality, most dogs will need to be treated for at least 4 months, although most will show improvement within the first 2 months. If the dog still has positive scrapings 6 months after continuous treatment, but is clinically normal (or dramatically improved) the owner should be informed that the disease can be controlled but that treatment is probably necessary for the rest of the dog's life.
Two species of this parasite have been recognized: Demodex cati, which resembles an elongated Demodex canis, and Demodex gatoi which has a short, squat appearance. Demodex cati is relatively rare, is usually found in the ears or on focal areas of alopecia on the face, and is not pruritic. It is easy to find on deep skin scrapings (being a follicular mite) and when (rarely) seen as a generalized infestation, usually points to an underlying ‘immunosuppressive' disease (diabetes mellitus, hyperadrenocorticism, FeLV, or FIV infections, etc.).
Demodex gatoi, which has been conjectured as being related to rodent Demodex species, tends to cause pruritus, may be difficult to find on skin scrapings, tends to be found superficially (in the stratum corneum) and is contagious to other cats.
In Demodex cati, successful treatment has been reported using lime sulfur (Lymdyp®: DVM Pharmaceuticals, Miami, FL). 1 cup: 1 gallon, q 5 days), a dilute amitraz (Mitaban®: Upjohn, Kalamazoo, MI ) solution of 125 ppm q 7-14 days, or 300 mcg/kg of ivermectin, PO or SQ, q24h. D. gatoi seems to respond best to the topical lime sulfur protocol1. When dipping any cat, an Elizabethan collar is helpful to prevent ingestion.
Scabies is an intensely pruritic, highly contagious, transmissible canine dermatoses caused by the epidermal mite Sarcoptes scabei var. canis. An artificial age predilection is often seen (young dogs). Clinically apparent disease may appear within one week of exposure to an affected animal. Sarcoptic mites can live up to 48 hours off a host in the environment. Although canine sarcoptic mites are fairly host specific to dogs and other canids, they may infest humans and cats as secondary hosts.
The life cycle from egg-larva-nymph-adult is 12-18 days and Adult mites live 4-5 weeks. Transmission is effected with newly fertilized female mites moving fairly rapidly on warm skin and burrow into the horny layer of the skin of their new host. The female usually lays its eggs with a few hours after burrowing. The eggs hatch within 3-8 days. Transmission is usually by direct contact with an infested dog or other canid (fox, coyotes, etc). Evidence supports clinical disease is a multi-factorial hypersensitivity reaction.
It is estimated that some member of household will have visible lesions in about 30% of the cases of canine scabies. Children are affected more commonly perhaps due to more extensive contact with the affected dog. Lesions in humans are papules, pustules and erythema most commonly on the forearms, neck, and along areas of elastic clothing contact.
Intense pruritus is the hallmark of canine scabies. Lesions on the dog are usually erythematous maculopapular eruptions with crusting, alopecia and often extreme secondary self-trauma. Crusts may be thick and yellowish. The lesions are primarily ventral in distribution with the most severe lesions affecting the pinnal margins, lateral aspects of the elbow, medial aspect of the foreleg, zygomatic arch area, and abdomen.Regional lymphadenopathy is common.
History of a rapid onset highly pruritic skin disease and possible contagion exposure as well as involvement of other dogs and people greatly increases the index of suspicion.The clinical features of scabies as noted are quite distinctive.
Diagnosis is confirmed by demonstrating via skin scrapings of the mites, eggs, and or fecal pellets. However, it is estimated that mites are found on skin scrapings in less than 50% of the cases, even after repeated scrapings. Therefore, it is essential to treat
empirically based on clinical impression. Fecal examination will sometimes show mites and eggs that were swallowed by the host during excessive grooming. A CBC with an absolute eosinophilia is suspicious (> 1300/cm). Proteinuria may be seen in the urinalysis. There is usually only partial response to previous corticosteroid treatment.
Treatment is most importantly the treatment of the dog and all in contact mammals (especially other dogs) with a scabicidal medication. Most commonly used are:
In order to contain contagion, it will be helpful to
Systemic corticosteroids may be used to control pruritus during the first week. Paradoxically, pruritus may actually increase during this time because of increased antigenic load.
Notoedric acariasis or feline scabies is an uncommon contagious mite infestation caused by the sarcoptid mite Notoedres cati characterized by crusting with extreme pruritus.
The disease is uncommon in most regions of North America, but may be found in localized endemic areas (southern California, Chicago area, Florida Keys, western Massachusetts, parts of the Canadian prairie provinces, etc). Notoedric acariasis may be increasing in prevalence with the advent of some newer insect-specific flea control products that do not kill acarids. Notoedric acariasis is seen predominantly in cats permitted to roam. Notoedres occasionally may affect dogs, humans and other mammals. Notoedric acariasis in dogs can mimic canine scabies.
Extreme pruritus, often starting on the head/face, but in advanced cases affecting the legs and feet, and occasionally the entire body. Lesions are often thick yellowish-gray crusts, associated with alopecia and lichenification.
Diagnosis is often suspected via a history of a rapid onset highly pruritic skin disease and possible contagion exposure. This is confirmed on skin scraping as the mites are usually easily demonstrated.
Treatment is similar to treatment of canine scabies. The author especially uses:
Cheyletiellosis or Cheyletiella dermatitis is a contagious mite infestation seen in domestic animals, wildlife and humans characterized by scaling and crusting. It may be seen more commonly in areas of the world where concerted flea therapy is not necessary or not consistent. Cheyletiella dermatitis may be increasing in prevalence on a wider basis with the advent of some newer insect-specific flea control products that do not kill acarids. Infestations have been reported in dogs, cats, rabbits, squirrels, poultry, foxes and humans. This disease may not be as uncommon as previously thought as many veterinarians in flea-active areas have a very low index of suspicion and do not look for this mite. It is reported that Cheyletiella mites may live in an animal's environment for extended periods of time (24 – 48 hours) off the host in places with optimal temperature and humidity. Cats participating in cat shows may be at highest risk for acquiring this parasite.
The causative parasites are not especially species specific: Cheyletiella yasguri (dog, cat, rabbit), C. blakei (cat), C. parasitivorax (rabbit, cat, dog). These are large mites (350-400 microns) readily easily identified by their prominent hook-like (‘Viking horn') mouth parts. The life cycle is completed on one host. The mites live on the surface and invade only the stratum corneum; Cheyletiella mites do not burrow deeper.
There may be an artificial predilection for young mammals due to increased chances of exposure (pet stores, kennels, shelters, etc).
There are definite zoonotic implications (as for scabies and notoedric mange) but less commonly suspected by MDs, despite documentation in the human medical literature. People in the house may develop visible pruritic distinctly papular lesions. It is estimated that some member of household is affected in approximately 30% of the cases. Children or others with more extensive contact with the affected animal are more likely to be affected. Lesions and sites in human are generally erythematous papules on the arms and neck, and around the belt- or bra-line. Lesions are pruritic. Cheyletiella is reported anecdotally to be self limiting in humans, once the condition is successfully treated on the pet.
Cheyletiellosis is predominantly a dorsal disease, often with dramatic scale, and .pruritus is variable and may be absent, especially in rabbits. Cats may have a dorsal miliary dermatitis (encrusted papules); there may be asymptomatic carriers. Dogs often have dorsal scaling, papules, or again may be asymptomatic carriers. Rabbits usually present with dorsal scaling and crusting.
The diagnosis may be based on history such as recent contact with other animals (cat or dog shows, pet shops, kennels, grooming establishments). The diagnosis is confirmed via clear tape preparation - Pick up crusting debris with clear tape and use as a cover slip on a slide with mineral oil, variable as far as ease of finding. Alternatively, superficial skin scraping - mites maybe easier to find than scabies mites, but still may be difficult to demonstrate.
Treatment is as per sarcoptic mange. The author especially uses:
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