Download Mangy Mutts: Diagnosis and Treatment of Common Mites in Dogs

Mangy Mutts: Diagnosis and Treatment of
Common Mites in Dogs and Cats
Joya Griffin, DVM, DACVD
Animal Dermatology Clinic: Louisville and Lexington, KY
Canine Demodicosis
Demodex mites are a follicular mites that is part of the dog’s normal cutaneous microfauna. They
are transmitted from the bitch to the puppies during nursing. Dogs born via c-section do not have
any Demodex mites.
A defect in the immune system of the skin or immunosuppression allows the mites to proliferate
in hair follicles. D. canis is the most common type of Demodex mite, however, several
morphologically different types of mites have been reported. The long-bodied mite, D. injae, is
often found on dogs with a greasy/oily skin and hair coat and is associated with a pruritic
dermatitis over the dorsal midline and sebaceous gland hyperplasia. Terrier breeds are overrepresented. D. injai has also been found within otic secretions. The short-bodied mite, D.
cornei, has been found in association with D. canis. Recent DNA sequencing indicates that this
short-bodied is a morphologic variant of D. canis and is not a separate species as D. injae is
thought to be. Regardless of the type of Demodex mites found in dogs, similar efficacy is seen
with treatment.
Juvenile-onset demodicosis is often seen in young dogs who have been afflicted by
endoparasitism, malnutrition and debilitation. This form is likely genetically based due to strong
breed predispositions. Dogs with juvenile-onset demodicosis should not be bred.
Immunosuppression
caused
by
chemotherapy,
neoplasia,
hypothyroidism,
or
hyperadrenocorticism predisposes adult dogs to demodicosis. A direct cause-and-effect
relationship with demodicosis is inapparent as many immunosuppressed animals do not develop
demodicosis. Clinical disease is divided into localized and generalized forms. Localized forms,
no more than four lesions up to 2.5 cm each, do not warrant treatment and spontaneously resolve.
Generalized disease can be severe with few cases spontaneously curing.
Clinical signs include mild erythema, comedones and scaling and can progress to partial or
complete alopecia with follicular papules, pustules and furunculosis. In severe cases crusting,
exudation, focal ulceration, and draining tracts may be seen. Lesions generally start on the face
and progress to the limbs and then to other parts of the body. Fever, lethargy and
lymphadenopathy can be present with generalized disease. Pedal demodicosis can cause severe
interdigital swelling and can be painful especially in large breeds.
Diagnosis of demodicosis is most commonly done via deep skin scrapes where capillary oozing
is achieved. Gentle clipping in longer haired breeds should be done. The skin should be squeezed
during or in between scraping to extrude the mites deep within the hair follicles. Best yield is
achieved by scraping primary lesions such as papules and pustules. Ulcerated areas should be
avoided. Even though, Demodex mites are a part of the normal microfauna, it is very uncommon
to find even one mite on deep skin scrape. If one mite is found on a single skin scrape, numerous
additional scrapes should be done as it is very rare to find even 1 Demodex mite in normal dogs.
The number and life stage of the mites should be recorded and the site they were obtained from
so that these same sites can be surveyed throughout treatment.
Trichograms are a useful technique for areas that cannot be scraped like the face, periocular
region and paws; however, a negative skin scrape does not rule out demodicosis and negative
trichograms should be followed by deep skin scrapes. Fifty to 100 hairs should be pulled in the
direction of hair growth and placed in mineral oil on a slide and covered with a cover slip.
Skin biopsy can be done in instances where skin scrape and trichogram are negative and the
index of suspicion for demodicosis is high. This may be necessary on the paws and in the Sharpei breed.
Direct examination of cytology from very exudative lesions can also yield Demodex mites.
Mites can also be found on fine-needle aspirates of lymph nodes. Secondary bacterial infections
should be identified and treated. Gram-negative infections are common with pedal demodicosis
with associated furunculosis.
Treat mild, localized disease with weekly chlorhexidine or benzoyl peroxide baths and monitor
for progression of lesions. Generalized demodex cases should be bathed once to twice weekly
with the aforementioned shampoos. The following treatment options are available:
1. 0.025- 0.06% Amitraz dips weekly or every 2 weeks. Medium to long-haired dogs should
be clipped and skin should remain dry between dips.
2. Milbemycin oxime once daily at 1-2 mg/kg.
3. Moxidectin as spot-on (Advantage Multi®) weekly. Note: This treatment option works
better in dogs with mild disease.
4. Ivermectin at 0.3- 0.6 mg/kg or moxidectin at 0.2- 0.5 mg/kg by mouth once daily. In
sensitive breeds, an initial dose of 0.05 mg/kg increasing every few days to the
therapeutic dose is recommended. Monitor for neurologic side effects.
Dogs should be evaluated monthly and treated beyond a negative skin scrape is achieved (no
mites or dead mites skeletons on cytology of exudates). Predisposing factors of demodicosis
should be identified and treated to maximize response to therapy. Long-term glucocorticoid
therapy should be avoided during treatment and in dogs with a history of demodicosis. Close
monitoring for recurrence of disease should be done for the first 12 months after remission.
Some adult-onset cases cannot be cured and remain on some form of therapy for life.
Feline Demodicosis
Cats can be afflicted by two species of Demodex mites, Demodex cati and Demodex gatoi as well
as a third unnamed morphologic variant. D. cati are part of the normal fauna residing within hair
follicles and sebaceous glands of cats and are analogous to D. canis in the canine counterpart.
Demodex cati is associated with systemic disease and a compromised immune system. D. gatoi,
on the other hand, is a contagious, superficial mites that causes extreme pruritus in otherwise
normal cats.
Demodex cati associated with lesions of alopecia, comedones, crusts, papules, seborrhea,
military dermatitis, erosions and ulceration. Pruritus is variable. If lesions are localized they are
generally on the face. D. cati can also cause ceruminous otitis alone or in conjunction with skin
lesions. Mites are diagnosed based on deep skin scraping, trichogram or biopsy. Patients should
be screened for retroviral infection and systemic or infectious diseases. Treat with oral
ivermectin 0.3 mg/kg SID or every other day or 0.0125% amitraz dips weekly (should only be
used if there is treatment failure with ivermectin due to the potential for toxicity).
Diagnosis of Demodex gatoi requires finding the mite on trichogram, superficial skin scrape or
fecal floatation. Due to the small number of mites normally present and the grooming behavior
of cats, actually identifying the mites is difficult. The best areas to scrape are non-alopecic areas
where the cat would have difficulty reaching. A “response to treatment trial” is the common
method of diagnosis. Treatment of choice requires weekly dipping with 2% lime sulfur for a
minimum of 6 weeks. Some have found treatment with daily or every other day oral ivermectin
at 0.3 mg/kg to be successful. Treatment failures have been seen. All cats in the household, even
asymptomatic individuals, should be treated. Studies are currently looking at the development of
a molecular diagnostic method to diagnose Demodex gatoi in cats. Recent DNA sequencing
confirmed two species of Demodex with D. cati resembling D. canis in dogs and D. gatoi
resembling D. brevis, the facial mites of humans that reside in sebaceous glands.
Sarcoptes
Sarcoptes scabiei var. canis is a contagious and zoonotic mite that causes intense pruritus in
hypersensitive dogs. The pattern of distribution affects sparsely haired areas such as the elbows,
hocks and ear margins. It can spread to the ventrum and face and usually is represented by
intense erythema as the primary lesion. Secondarily, excoriations, scaling, lichenification,
hyperpigmentation and secondary infections occur. Most infected dogs itch a few days after
being infected by scabies mites but have mild symptoms. Three to four months later, intense
pruritus develops. A positive pinnal-pedal response is present in most affected individuals.
Diagnosis is done via demonstrating the mites on superficial skin scrapes. The mite is difficult to
find due to small numbers of mites on the infected patient. A response to treatment is the most
common diagnostic method. Treatment with weekly lime sulfur dips, weekly oral ivermectin, bimonthly subcutaneous ivermectin, and topical AdvantageMulti® or Revolution® every two
weeks for 4-6 weeks to stop the life cycle of the mite which is 10-21 days. All in-contact animals
should be treated even if asymptomatic. Environmental decontamination is not necessary.
Notoedres
Notoedres cati, also referred to as feline scabies, is associated with pruritus, scaling and crusting
of the head and face. Mites are recovered on superficial skin scrapes and the mites can be easily
spread to all in-contact animals and humans. Treatment is like that of scabies.
Otodectes
Otodectes cynotis is a contagious mite that has a 3 week life cycle. The mite infects the vertical
and horizontal ear canals of dogs and cats. The mite feeds on surface keratin and can cause
irritation and local trauma. Animals with mite produce copious amounts of sebum that is dark in
color due to blood and ear mite feces and causes an occlusive otitis externa. The mites can spread
to the face, back claws and face due to scratching. Milliary dermatitis can occur in cats.
Diagnosis is based on identifying the mites in otic debris in mineral oil. Many licensed topical
therapies are available. Systemic therapy with ivermectin or topical miticides is also effective.
All in-contact animals should be treated and the environment cleaned as the mite can live off of
the host for several weeks.
References
1. Muellar, RS, et al. Treatment of demodicosis in dogs: 2011 clinical practice guidelines.
Vet Derm, 23; 86- 96.
2. Ordeix, L, et al. Demodex injai infestation and dorsal greasy skin and hair in eight
wirehaired fox terrier dogs. Vet Derm, 20; 267-272.
3. Milosevic, MA, et al. PCR amplification and DNA sequencing of Demodex injai from
otic secretions of a dog. Vet Derm, 24, 286-288.
4. Ravera, I, et al. Small Demodex populations colonize most parts of skin of healthy dogs.
Vet Derm, 24, 168- 172.
5. Fondati, A, et al. Prevalence of Demodex canis-positive healthy dogs at trichoscopic
examination. Vet. Derm, 21, 146-151.
6. Frank, LA, et al. A molecular technique for the detection and differentiation of Demodex
mites on cats. Vet Derm, 24, 367-369.
7. Beale, K. Feline demodicosis: a consideration in the itchy or overgrooming cat. J Feline
Med Surg, 14 (3), 209-213.
8. Campbell, KL. Small Animal Dermatology Secrets. Hanley and Belfus, 2004.
9. Terada, Y. Sarcoptes scabiei var. canis refractory to ivermectin treatment in two dogs.
Vet Derm. 21, 608-612.
10. Curtis, C. Current trends in the treatment of Sarcoptes, Cheyletiella and Otodectes mite
infestations in dogs and cats. Vet Derm. 15, 108-114.