Liz is a licensed veterinary medical technologist. She acquired a B.S. in veterinary medical technology from Lincoln Memorial University.
What Is Demodex?
Demodex is a genus of parasitic mites that live in or near the hair follicles of mammals. It is often associated with the development of patchy hair loss and/or mild to severe dermatitis (itching and inflammation of the skin) in dogs and sometimes cats.
The Demodex species that affect dogs are:
- Demodex canis
- Demodex injai
- Demodex sp. cornei
The Demodex species that affect cats are:
- Demodex cati
- Demodex gatoi
Most Demodex species are considered to be normal mammalian fauna. This means that they normally live on the skin of certain mammals in small numbers; as long as the animal's immune system keeps the population of mites on the skin in check, most Demodex species do not cause any harm to their host.
Neonates (newborns) are thought to contract mites from the dam via direct skin-to-skin contact. Despite this direct contact, in most cases, individual animals do not develop any clinical disease (obvious signs or symptoms).
All stages of the mites' life cycle (eggs, larvae, nymphs, adults) live within the lumen of hair follicles and within sebaceous gland ducts, although some species are more commonly found in the stratum corneum (outermost layer) of the skin. Development from egg to adult takes about 20 to 35 days depending on the species, and the entire life cycle is completed entirely on the host. Six-legged larvae hatch from fusiform-shaped eggs, undergo several molts to become eight-legged nymphs, and ultimately become adults. Adults are eight-legged, slender, and elongated mites. Their appearance is often described as cigar-shaped.
When Demodex Causes Disease
Although most Demodex species are considered normal mammalian fauna, overgrowth of these mites is often associated with the development of patchy hair loss and/or mild to severe dermatitis in dogs and (although less commonly) in cats. In cases of demodicosis caused by Demodex sp. cornei or D. gatoi in cats, disease is thought to be caused by the actual infestation itself rather than an overgrowth of mites, and can be associated with pruritus (itching and irritation) in the absence of pyoderma (skin infection associated with pus).
In dogs, affected areas may be localized (occurring only in one or multiple small areas) or generalized (occurring widely over most or all of the body); both forms may present in either juvenile or adult dogs. Pruritus does not occur in uncomplicated infestations; however, pruritus can be seen with secondary bacterial pyoderma. In dogs, localized demodicosis—characterized by a mild, nonpruritic, patchy alopecia (hair loss) on the head or limbs—usually develops in puppies less than 6 months of age. Most cases of juvenile-onset localized demodicosis resolve spontaneously without treatment. Most cases are attributable to an overgrowth of mites believed to occur because of an underlying systemic disease or immune defect.
With Demodex sp. cornei, however, the infestation itself is thought to cause disease. Physical exam findings include alopecia (which may involve several large areas of affected skin), erythema (redness), and often secondary superficial or deep pyoderma. Lymph nodes may be enlarged, and when pyoderma is present, pruritus may develop.
In felines, cats with localized demodicosis develop alopecia and crusts, as well as some scaling around the face, neck, and eyelids, with some varying degree of hyperpigmentation (darkening of the skin). Generalized demodicosis due to overgrowth of D. cati is usually associated with underlying systemic disease. Cats infested with D. gatoi are pruritic and may excessively lick or groom affected areas, but this species is not associated with underlying disease.
Canine demodicosis due to D. canis is common; however, disease due to D. injai or D. sp. cornei in dogs appears to be rare. Feline demodicosis due to D. cati is rare and D. gatoi infections are even less common, although most all cases are reported from the southeastern United States.
Host Associations and Transmission
Demodex spp. are host-specific mites of mammals; mites have not been shown to cross-infest between dogs and cats, nor are they transmitted to people. Neonates are thought to acquire mites from their dam via direct skin-to-skin contact during nursing.
Transmission of mites may also occur during direct contact between older animals, but Demodex is not considered contagious as most animals that develop generalized demodicosis are thought to have an underlying immune defect.
However, Demodex gatoi (feline species) is thought to be contagious among cats through direct contact.
Sites of Infestation
Demodex canis and D. cati infest hair follicles and sebaceous glands. Mites may occasionally be reported from other tissues (e.g., lymph nodes, intestinal wall, kidneys, thyroid glands) following dissemination via blood or lymphatic drainage.
Early studies of nursing neonatal puppies have found D. canis mites are typically within the skin of the face initially, and then over time the mites are transferred throughout the skin of the entire body. Mites are not found in the skin of stillborn puppies or puppies born by Caesarian that are not allowed to nurse. Localized demodicosis in dogs most commonly develops on the head or limbs, yet the lesions of generalized canine demodicosis may develop anywhere on the body. Demodex gatoi infestation in cats is most frequently reported from the groin, ventral chest, and sometimes the limbs.
The immunopathogenesis of demodicosis is not fully understood; in most cases, an underlying cause is not identified. Although a responsible condition is not always identified, many cases of generalized demodicosis appear to be the direct result of underlying diseases that compromise the immune system. Excessive cortisone usage, poor nutrition, chemotherapy, and underlying cancer, diabetes, or other chronic disease processes have all been associated with the development of generalized demodicosis in individual animals. Accordingly, dogs and cats with generalized demodicosis should be carefully evaluated for potential underlying disease states. No specific deficits in innate or humoral immunity have been identified in dogs with generalized demodicosis; however, some studies suggest that cellular immunity may be compromised in some individuals that go on to develop generalized demodicosis.
Demodicosis due to D. canis, D. injai, and D. cati is diagnosed by microscopic examination of deep skin scrapes from affected areas of alopecia. Alternatively, in uncooperative dogs or sensitive areas in which skin scrape is difficult (i.e., feet, interdigital regions), hairs may be plucked from an affected area and placed in mineral oil on a slide for microscopic examination.
Because Demodex sp. cornei and D. gatoi in cats reside within the stratum corneum, superficial skin scraping or tape impression offers a better method. Because the pruritus associated with D. gatoi infestations leads to removal of the mites by grooming, they often are difficult to find. In rare cases of “occult demodicosis,” (no mites are observed with either skin-scraping or hair-pluck techniques), a skin biopsy may demonstrate Demodex mites. The mites (or mite fragments) can be seen within the lumen of the hair follicles or (rarely) within the sebaceous glands/ducts, depending on the type of mite. This technique may be necessary in Demodex cases involving the feet and in the Chinese Shar Pei.
In canines, most cases of localized demodicosis resolve spontaneously without treatment. If treatment is desired, a rotenone-based insecticide ointment (Goodwinol) has been approved. Generalized demodicosis may require extended, aggressive therapy to resolve disease.
Comprehensive treatment should include use of an effective miticide, evaluation for any underlying disorders and appropriate treatment when found, antibiotic therapy when pyoderma is present, and spaying of female dogs to prevent recurrence during subsequent heat cycles. Several months of treatment may be required to eliminate the mites. Selected treatment should be continued for 1 to 2 months after mites are no longer detected on skin scrape. Amitraz dip (Mitaban) at 250 ppm every 2 weeks is the only approved miticidal treatment for generalized demodicosis in the United States. Hair should be clipped throughout treatment; dogs should be allowed to air-dry or should be dried with a blow dryer after each application. Use of a benzoyl peroxide shampoo prior to the application of amitraz dip is recommended; dogs should not be shampooed between applications. Some practitioners recommend weekly dips or a more concentrated formulation (e.g., 500 ppm) in refractory cases or to clear dogs more rapidly.
Other miticidal treatments not labeled in the United States include high-dose oral ivermectin, oral milbemycin oxime, topical moxidectin, and injectable doramectin. Some dogs, particularly herding breeds, may have mutations in their MDR1 genes and thus have increased risk of toxicity to these classes of drugs. Treatment should be discontinued immediately if any neurologic signs develop. Ivermectin may be given orally at escalating doses using 100 µg/kg increments. Milbemycin oxime has also been used daily at doses ranging from 0.5 to 2 mg/kg, with does escalated gradually, building to a final dose of 1.5 to 2.0 mg/kg. Doramectin may be injected subcutaneously once a week at the dose of 600 µg/kg in dogs negative for the MDR1 gene mutation.
Treatment of affected cats is more difficult. No products are labeled for demodicosis in cats, though lime sulfur dips have been reported effective. Dips should be performed weekly for 6 weeks with 3.1% solution. Ivermectin has been used once weekly at 0.3 mg/kg orally for four consecutive weeks. Amitraz has also been used in cats every 5 to 7 days for 4 to 6 weeks. Treatment should be continued for 1-2 months after mites are no longer detected on skin scrape.
Control, Prevention, and Public Health Concerns
For intact female dogs that develop generalized demodicosis, spaying is recommended because they may experience relapse of disease in subsequent heat cycles. The development of demodicosis was long believed to have a genetic predisposition, and as a result, some veterinarians discourage breeding affected animals. The propensity to develop localized demodicosis is hereditary; however, the hereditary nature of generalized demodicosis has not been clearly demonstrated. As Demodex mites are host-adapted, there is no zoonotic potential to humans in either canine or feline demodicosis.
- Jennifer Rutan, DVM. "Treating Canine Demodicosis." http://www.banfield.com/getmedia/48158ee0-00c5-4c8c-9e4e-5562ada2abab/2_2-Treating-canine-demodicosis
- Notes from Lincoln Memorial University Veterinary Medical Technology program courses.
- Personal experience as a veterinary technician and with own pets who have had demodectic mange.
This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
© 2018 Liz Hardin