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SPECIAL FOCUS PARASITOLOGYContinuing Education Article #5 .. :; Vol. 13; .No, ~. M~y 19,.91 783

A REPRINT FROM

Parasitic Mites of Dogs and CatsKEY FACTS• In dogs and cats, parasitic mites can cause Irritation and annoyance, may Induce localized Infection, and can be

debilitating or fatal.• Mites lack natural enemies and can be resistant to parasiticIdes; some species can lower host Immunity.• Some mite Infestations are easily eliminated from the animal and environment. Others are difficult or Impossible to

eradicate. .• Prompt diagnosis of mite Infestation and Identification of the mite species as well as appropriate treatment are requisite

to eliminate the parasite, to Institute any ancillary treatment, a.nd to advise the owners regarding contagion of theparasite or any possible predisposing genetic factors of the host.

• In some cases, extralabel therapy with such agents as amltraz, ronnel, or Ivermectln Is the most effective treatment.Owners must give Informed consent before the extralabel treatment Is Initiated.

Upper Keys Veterinary ClinicIslamorada. Florida

Robert H. Foley, DVM

RRASITIC MITES ace membe" of the class Mach­nida, order Arachina (see the listing on Mite Taxonomy).Mites have a four-stage life cycle: egg, six-legged larva,eight-legged nymph, and eight-legged adult. Except forchiggers (Trombiculidae), of which only the larval stage isparasitic, mites of all four stages are parasitic.

The three suborders of mites in the order Arachina con­sist of animals of diverse sizes, shapes, and distinguishingcharacteristics (Table I). The host anatomic areas preferredby various mite species differ (Table II) as do the geo­graphic distribution (Table. III) and potential for contagion

.' to .other animals and to h'umans 1.2 (Table IV). Because thej. "':":_c~inical significance and management of mite infestation.: ~;~.:~u,epend on the mite species, this article discusses each of

'the commonly encountered mites separately.

the litter. Susceptible young dogs reportedly can contractDemodex canis mites by direct and close contact with aheavily parasitized carrier. 18

The presence of Demodex canis mites is considered to bea disease state when excessive numbers of mites of all fourstages of the life cycle are present in a skin scraping froman animal with clinical signs. 19 Demodicosis is also termedfollicular, red, pulJPY, squamous, pilosebaceous, or Aca­rus mange. Demodex mites reproduce and lay eggs in thehair follicle and associated sebaceous and apocrine sweatglands. The mites puncture cells and ingest the cell con­tents; this feeding activity produces keratinization thatplugs and distends the follicle. Proliferation of the mites,with subsequent rupture of the hair follicle, allows the par­asites to enter the bloodstream, lymphatics, lymph nodes,

J.;.and various body organs. Inflammation and foreign body

DEMODEX SPECIES ' '., response also occur. 20

Clinical Manifestations in Dogs Demodicosis occurs in three clinical forms: localized de-A small population of Demodex canis mites is a normal modicosis, generalized Uuvenile or adult) demodicosis,

finding on or in the skin of healthy dogs. The elongated and chronic pododermatitis. The localized form is the mostmite (Table I) lives its entire 20- to 35-day life cycle in the common and usually involves the face, skull, ear canal,hair follicle, leaving only to cross to another hair follicle2 .16 forelegs, or trunk. Affected dogs may have alopecia, vary-(Figure 1). The mites are transmitted to puppies by contact ing degrees of scaling, hyperpigmentation, minimal pruri-with the dam during the first two to three days of life. 17 tus, erythema, and bacterial infection. The mites mayMites can also be transmitted from one pup to another in elude discovery. Multiple scrapings from squeezed hair

Copyright © 1991, Veterinary Learning Systems Co., Inc. All Rights Reserved. Printed in USA

784 The Compendium • Small Animal

Mite Taxonomy (Order Acarina)1Class Arachnida: Head, thorax, and abdomenare fused. Mouthparts in capitulum; antennaeand mandibles missing. Six-legged larvae,eight-legged nymph and adult stages.

Order ArachinaSuborder Prostigmata

Family DemodicidaeDemodex canisDemodex catiUnnamed Demodex species

Family CheyletiellidaeCheyletiella yasguriCheyletiella blakei

Family TrombiculidaeWalchia americanaTrombicula alfreduggesiTrombicula autumnalis

Suborder Astigma: Respiratory poresabsent; respiration occurs throughintegument

Family SarcoptidaeSarcoptes scabiei var. canisNotoedres cati

Family PsoroptidaeOtodectes cynotis

Subfamily ListrophoroideaLynxacarus radovskyi

Suborder Mesostigmata: Respiratory poreson mid body

Family HalarachnidaePneumonyssoides caninum

Family DermanyssidaeDermanyssus gallinae

Suborder Metastigmata: Ticks

follicles on the margin of lesions may be needed.Skin scraping suffices to diagnose localized or general­

ized demodicosis; whereas in cases of pododermatitis, skinbiopsy sometimes is necessary to establish a diagnosis. Lo­calized demodicosis is most common in intact purebreddogs (76 %) younger than one year of age. 18 Ninety percentof cases of localized mange resolve spontaneously in fourto eight weeks. Underlying transient stresses (e.g., adoles­cence, estrus, endoparasites, growth, nutrition, vaccina­tion, surgery, and pregnancy) have been incriminated andmay contribute to the disease. Sex, haircoat length, seba­ceous gland size, and hypothyroidism do not appear to befactors in the development of localized demodicosis.'8.19.21

Ten percent of dogs with the localized form deteriorate togeneralized juvenile demodicosis. The generalized form in-

volves large areas of the body and causes alopecia (in morethan 10 areas), erythema, and varying degrees of crusting,follicular plugging, and hemorrhage. A rancid seborrheicodor, folliculitis, furunculosis, cellulitis, deep pyoderma,pruritus, and peripheral lymphadenopathy often accompanygeneralized juvenile demodicosis. The condition can alsooccur without major associated reactions2.'7-'9.22 (Figure 2).

In one study of 821 dogs with generalized juvenilemange, 87 % of the cases occurred in animals older thanseven months of age; most of the subjects were intact pure­breds (80%). Age and familial predisposition were themost important factors. 18 Two mechanisms have been pro­posed to explain the inherited immunologic predispositionto generalized juvenile demodicosis. The first explanationis that a genetic immune abnormality allows massive miteproliferation. The heavy mite population induces a hu­moral substance (B-cell stimulation) that in turn suppressescell-mediated (T-cell) immunity. Treatment is directed atelimination of the mites to restore T-cell function. 23-25

The second proposed mechanism is that genetic predis­position to pyoderma complicates the generalized juveniledemodicosis and suppresses lymphocyte blastogenesis (Band T cells). The pyoderma suppresses serum lymphocyteimmunoregulatory factors in proportion to the degree ofinfection. Therapy would therefore be directed at the skininfection. 22 Immunosuppressive agents, such as cortico­steroids, should not be used in animals with generalizedjuvenile demodicosis. Because of the inherited predisposi­tion to the condition, the American Academy of VeterinaryDermatology recommends that dogs with generalized de­modicosis should be sterilized.26

Demodectic pododermatitis tends to be a chronic digitaland interdigital disease often complicated by pyoderma.Certain breeds are at increased risk (see the listing on Ca­nine Breeds Predisposed to Demodicosis). Biopsy may benecessary to reveal the mites. In many cases, the conditionis never cured. 2.27

Adult-onset demodicosis may not be hereditary. Mostcases are secondary to iatrogenic Cushing's syndrome, at­opy, immune deficiencies, diabetes mellitus, heartworms,malignancies, use of immunosuppressive agents, or deeppyoderma. Patients with the adult-onset disorder must bethoroughly examined and checked for other parasites anddisease processes. A complete blood count, blood profile,and endocrine screening should be performed to identifyany inciting factors needing treatment. Scottish terriers andWest Highland white terriers seem particularly prone toadult-onset demodicosis complicated with atopy and deeppyoderma (Figure 3). Adult-onset generalized demodicosiscan necessitate euthanasia. 2.27-29

Treatment of Canine DemodicosisTherapy for canine demodicosis depends on its form and

complications. Localized demodicosis has a good progno­sis; 90% of cases remit spontaneously within four to eight

weeks without treatment. If the patient's owner insists onsome form of intervention, topical 1% rotenone or follicu­lar flushing products with benzoyl peroxide may be ap­plied. 18

F;R THE 10% of locali"'l cases 'hat del"io"'e to gen­eralized demodicosis, the prognosis is less optimistic andindividualized therapy is indicated. From 30% to 50% ofgeneralized juvenile demodicosis cases resolve spontane­ously. Acaricidal therapy may not be necessary immedi­ately; the clinician should monitor the patient's progressclosely. Skin scrapings performed at two- to four-week in­tervals indicate when increasing mite population and pre­dominance of immature forms dictate more-aggressivetreatment. Review of the animal's pedigree could revealthe likelihood of spontaneous remission.2.17-19

Treatment of generalized demodicosis (juvenile andadult-onset) should be directed at simultaneous eliminationof mites and any underlying pyoderma. Currently, amitrazis the only agent approved for use as a Demodex miticidein the United States. The manufacturer advises that 10.6ml be diluted in two gallons of water (250 ppm = 0.025 %)and applied every two weeks to the dog's dry haircoal.Gloves must be worn during application of amitraz.

Before amitraz application, the haircoat should beshaved and cleansed with a follicular flushing shampoo ora therapeutic shampoo (e.g., with povidone-iodine orchlorhexidine). Areas of deep pyoderma and furunclesshould be avoided during dipping to minimize toxicity as­sociated with amitraz absorbance. 27

Extralabel use of amitraz dramatically improves curerates; an animal is considered cured if skin scrapings arenegative and the animal lacks clinical signs six months af­ter the last treatment. One study24 found that when 0.03 %amitraz (6 ml of 19.9 % amitraz in two gallons of water)was applied weekly rather than every two weeks, the curerate for generalized demodicosis can rise from 20% to75 %. Halving the diluent (6 ml amitraz in 1 gallon of wa­ter) to double the dose to 0.06 % can raise the cure rate upto 80 % with minimal toxicity. Amitraz toxicity is mani­fested as increased sleepiness, depression, and anorexiaduring the first 24 hours after treatment. More-extremesigns of toxicity, such as ataxia, polyuria, polydipsia, hy­pothermia, seizures, pruritus, erythema, hyperglycemia,and glucose intolerance, may occur. 30.31 Death is highly un­likely.30

If a doubled dose of amitraz is administered weekly, hy­perglycemic and insulin-suppressing effects require specialcaution for diabetic animals. 31 Humans with diabetes mustwear gloves when applying amitraz. Weekly administra­tion of 0.05% amitraz seems most efficacious; but petowners must be advised that this regimen is extralabel. 30

In France, amitraz concentrations of 0.05% and 0.10%

The Compendium • Small Animal 785

have reportedly been effective and produced no toxic sideeffects. 32 Also in France, an amitraz-impregnated collar ismarketed for Demodex and tick control,32 Treatment fail­ures may be related to premature cessation of treatment orfailure to correct underlying stress or infection. Months ofweekly dipping may be needed to effect a cure; there is noprescribed number of dips.

Extralabel use of ronnel can be tried to treat generalizedjuvenile demodicosis if amitraz fails. Ronnel is mixed as a4% solution with propylene glycol (Scott's formula).24 Theagent can be dispensed in a 4-ounce childproof amber med­icine bottle containing 18 ml of 33.3 % ronnel solution plus100 ml of propylene glycol. The preparation is stable forabout one month. One third of the dog's body is painteddaily so that each area is treated once every three days insequence. Ronnel is effective in 90% of cases but is irritat­ing to the skin and highly toxic to animals and humans. 19Dogs to be treated with ronnel (or any organophosphate)should be free of heartworm infection before treatment isinitiated. Demodex canis is resistant to ectoparasiticidesless potent than ronnel.

DEMODECTIC pododennalitis can he "eated withweekly immersion in double-strength amitraz (0.05%) or4 % topical ronnel. Fresh daily amitraz can be applied (lml of 19.9% amitraz per 30 ml of propylene glycol); how­ever, oxidation makes this topical preparation unstable.Aqueous trichlorfon (3 %) solutions may be used as a topi­cal therapy but are less effective than ronneP9; this use oftrichlorfon is also extralabel.

For all miticidal therapies, skin scrapings must be moni­tored at two- to four-week intervals. Counts or estimates ofthe numbers of live and dead mites should be made andtherapy continued for three to four weeks after scrapingsare negative. Recurrence is possible, and lifelong amitrazdips may be necessary. 28.33

Concurrent pyoderma must be treated simultaneously.Skin culture and sensitivity studies are indicated in compli­cated cases of demodicosis. Coagulase-positive staphylo­cocci are the most common isolate, but Proteus or Pseudo­monas organisms may be present. Pseudomonas seriouslychanges the prognosis because it can cause fatal septice­mia. 18 An antibiotic, such as erythromycin, lincomycin,oxacillin sodium, cephalosporin, or chloramphenicol, maybe used until the culture and sensitivity report returns. An­tibiotics should be continued weeks beyond healing. 25 Cli­ents should be advised of the zoonotic potential of the pet'sinfected skin.

Vitamin E (up to 400 U orally twice a day) and fatty acidsupplements may quell skin inflammation in dogs withgeneralized demodicosis and are useful for treating any un­derlying atopy. 33 Immune stimulants, such as levamisole orinjectable bacterins, have not been successful against mites

786 The Compendium. Small Animal

TABLE ISize and Identifying Characteristics of Parasitic Mites of Dogs and Cats2-6

Mite

Demodex canis

Demodex cati

Unnamed Demodex species

Cheyletiella yasguri

Cheyletiella blakei

Trombiculidae (chiggers)

Sarcoptes scabiei var. canis

Notoedres cati

Otodectes cynotis

Lynxacarus radovskyi

Pneumonyssoides caninum

Dermanyssus gallinae

Size of Adult Female(lAm) Characteristics

40 x 225 Spindle-shaped eggs; elongated body,striations

30 x 200 Oval eggs; smaller and slimmer bodythan Demodex canis

30 x 110 Short, blunt abdomen; superficial skinparasite

265 x 500 Cone-shaped sensory organ

265 x 500 Huge mouthhooks, heart-shaped sensoryorgan; surface mite

210 x 400 . Orange-red, six-legged parasitic larva;hairy body; surface mite

250 x 400 Terminal anus; long, unsegmentedpedicel

200 x 240 Dorsal anus, body striations

300 x 400 Long legs, short pedicel; males havepretarse on all four pairs of legs; surfacemite

250 x 515 Hair-clasping sternal plates, elongatedbody; surface mite

150 x 400 Long legs, small palps; often confusedwith Dermanyssus mites

150 x 400 Long legs, stocky palps; deeplyembedded, red poultry mites; surfacemites

but may aid pyodenna therapy. 23.28

The extralabel use of ivennectin has produced disap­pointing results against Demodex mites, although it ishighly effective against other mites. 34,35 Ivennectin para­lyzes susceptible mites by potentiating the neuroinhibitorv-aminobutyric acid (GABA), thus blocking postsynapticneuromuscular potentials, and is lethal to the parasite.Ivennectin does not cross mammalian blood-brain barriersto reach the GABA receptors. 35 Ivennectin can cause po­tentially fatal idiosyncratic reactions in collies, sheepdogs,and related crossbreeds and should not be used in theseanimals. 36.37 Dogs should be screened for heartwonn infec­tion before receiving ivennectin therapy; the preciseweight of all animals, dogs or cats, should be measured todetennine the correct dose.

A 1% preparation of ivennectin provides 10 mg/ml(10,000 Ilg/ml). In one study, two 400-llg/kg injections ofivennectin given two weeks apart were effective againstDemodex canis. 38 Another trial of the same dose at weeklyintervals did not resolve the infestation but seemed to pro-

vide some reduction of clinical signs. 34 The efficacy ofmilbemycin oxime against Demodex canis is under study.

Clinical Manifestations in CatsFeline demodicosis is caused by the follicular mite Dem­

odex catil.2•9 (Figure 4) and a much less common unnamedDemodex species, which is found only in the stratum cor­neum of the cat's skin. 39•4O The size and shapes of thesemites differ from those of Demodex canis3 (Table I). Bothspecies are rare. Feline demodicosis manifests itself in twofonns. The localized fonn exhibits erythematous patchesof alopecia along with scaling and crusting of the eyelids,face, chin, or neck (Figure 4). Ceruminous otitis may beseen. Multiple skin scrapings disclose the parasite. Sponta­neous remission can occur. Generalized feline demodicosisis usually associated with an underlying disease (e.g., dia­betes mellitus, hyperadrenocorticism, endocrine alopecia,feline leukemia virus infection, feline immunodeficiencyvirus, or an autoimmune disease).41-44

Generalized feline demodicosis may be more common in

788 The Compendium • Small Animal

Figure 1A Figure 18

Figure 1-(A) Characteristic Demodex canis mite measuring 40 /-1m x 225 /-1m. (x60) (8) Demodex canis egg. (x60)

Figure 2-A 10-month-old female akita with generalized juveniledemodicosis. Pyoderma was minimal relative to the extent ofDemodex canis lesions.

Burmese and Siamese cats than in other feline breeds.2.39

Extensive lesions of erythema, alopecia, crusting, and hy­perpigmentation can involve the head, neck, legs, andtrunk. Eosinophilia and pyoderma may occur. Intensepruritus can occur with infestations of the unnamed Demo­dex species. 3

Treatment of Feline DemodicosisThe prognosis for treatment of feline demodicosis is

good. Treatments include 2.5% lime-sulfur dips, carbarylshampoos, and malathion dips.2.42 Carbamate products,however, are not approved for use on kittens or nursingpuppies. Organophosphates should only be used cautiouslyin cats. An extralabel regimen of weekly half-strength ami­traz dips (0.0125 %) is effective against feline demodico­sis. 45 Sedation and salivation are transient side effects,especially when the amitraz preparation is used full­strength. 45 Diabetic cats with demodicosis should betreated with miticides other than amitraz. 31

CHEYLETIELLA SPECIESClinical Manifestations

Cheyletiella yasguri of dogs and Cheyletiella blakei ofcats are large, surface-feeding mites that live in keratin(Table I). Their 35-day life cycle is spent entirely on thedog or cat. The mite has enormous hooked mouthparts andcombed legs; it attaches its eggs to hair. The mites are verymobile and contagious by direct contact; the so-calledwalking dandruff can spread rapidly through a kennel orcattery. Puppies and kittens are most susceptible.

Cheyletiella mites are not host specific, and a referencetext is advisable for correct identification of the species.The hallmark of Cheyletiella is the moving white flakesalong the dorsal midline and head of the dog and cat.Scraping, combing, or applying transparent adhesive tapeto the suspect areas aids in disclosing the large, visiblemites. Magnifying loupes and selective removal of ques­tionable flakes or hairs represent the quickest method.Some fastidious cats may require skin scrapings or fecalflotations to reveal mites.2.4.9.46.47

Dogs experience more pruritus associated with cheyle­tiellosis than do cats. The canine disease may resembleseborrhea oleosa or fleabite dermatitis. Affected dogs havescaly, oily skin. Cats may appear to have seborrhea siccawith scales and red scabs, or they may show no signs atall. Humans, especially cattery personnel, are highly sus­ceptible to Cheyletiella infestation. Pruritus, erythematouspapules, and pustules appear on the chest, arms, thighs,and abdomen. The human disease is transient (threeweeks) without reexposure.4.11-13

TreatmentTreatment of Cheyletiella mite infestation can be accom­

plished by using lime-sulfur dips, carbaryl shampoo or 5 %dust, 0.5 % malathion dips, or pyrethrins weekly for fouror five treatments.2.9 Although amitraz has not been ap­proved for use against Cheyletiella, this agent is effective

TABLE IIHost Anatomic Areas Preferred by

Canine and Feline Mites2,7,8

Mite

Demodex species

Cheyletiella species

Trombiculidae

Sarcoptes scabiei var. canis

Notoedres cati

Otodectes cynotis

Lynxacarus radovskyi

Pneumonyssoides caninum

Dermanyssus gallinae

Preferred Location on Host

Localized: follicles of face,skull, ear canal, forelegs;

Generalized: anywhere andeverywhere

Surface of dorsal midline

Surface of head, legs, andventral areas

Epidermis of ear tips, elbows,and glabrous areas

Epidermis of ears, face, andfeet

Surface of ear canals andperiauricular areas

Surface of perineum, tailhead,and tail tip

Nasal sinus, nasal passages

Surface of legs and back

The Compendium • Small Animal 789

Canine Breeds Predisposedto Demodicosis2,5.18,19

Generalized Juvenile DemodicosisAfghan hound, beagle, Boston terrier, boxer,Chihuahua, Chinese shar peL chow chow,collie, dalmatian, dachshund, Dobermanpinscher, English bulldog, German shepherd,Great Dane, Old English sheepdog, pointer,pit bullterrier, pug, Staffordshire bullterrier

Chronic Demodectic PododermatitisGreat Dane, Newfoundland, Old Englishsheepdog, Saint Bernard

Generalized Adult-Onset DemodicosisCocker spaniel, Old English sheepdog,Scottish terrier, West Highland white terrier

can be killed by carbaryl shampoos, powders, or dips;pyrethrin; or extralabel use of amitraz (0.025 %).2.5.9.32.51

on dogs (0.025%); one treatment is sufficient. 48 Subcuta­neous ivermectin (300 J.lg/kg) repeated after a five-weekinterval is effective and useful for miticide-resistant casesand may be ideal for cattery and kennel infestations. 14 ,49Regardless of the treatment used against Cheyletiella, all ofthe animals in the household or facility must be treated.

TROMBICULIDAEClinical Manifestations

Trombiculiasis is infestation by parasitic, six-legged, lar­val chiggers. Dogs, cats, and humans can be parasitized by20 of the more than 700 species of chiggers. Infestation ismost prevalent during the late summer and fall and in ani­mals frequenting fields or woodlands where the larvalmites are contracted directly (Table III). The nymphs andadult chiggers are free-living and not parasitic. The brightorange-red mites are surface feeders; their salivary secre­tions induce intense pruritus that lasts longer than the mitesare present on the body. Alopecia, pustules, and scaling ofthe head, ears, ventral trunk, legs, and paws can occur.The entire body can be afflicted; self-inflicted injury is of­ten a problem.

Diagnosis and TreatmentDiagnosis can be made by scraping the mite from the

lesion, but the mite may already have detached from theanimal.2·5.9,47.5o.51 Thus, chigger infestations might be morecommon than they are believed to be. Mites that are present

SARCOPTESClinical Manifestations

Scabies caused by the mite Sarcoptes scabiei var. canis isoften misdiagnosed as contact allergy, food allergy, atopy,or fleabite dermatitis. Many pruritus-producing skin dis­eases can resemble scabies. 52 This mite usually appears ondogs, occurs only rarely in cats,53.54 and spends its 17- to21-day life cycle in epidermal pockets. The large femalemite lays three to five eggs per day in freshly burrowedtunnels (Table I). The male mite, along with mites in thelarval and nymph stages, lives in vacated burrows. Themale dies after copulation. Sarcoptes mites have a long,unsegmented pedicel and a terminal anus. I .2

LTENSE pmdtu, iuducod by hypmeu,itivity to buc­rowing female mites is a consistent clinical sign. The mitetargets the pinnae, elbows, back, chest, abdomen, or hair­less areas. The entire body can be affected. Alopecia, hem­orrhagic crusts, and papules are worsened by self-inflictedinjury. The skin becomes Iichenified, and secondary infec­tion and lymphadenopathy occur. The animal can becomedebilitated; but well-nourished, well-groomed dogs alsocan have scabies. Frequent grooming of dogs and frequentinsecticidal shampooing can cause and mask scabies insome pampered pets; the resultant condition has beencalled scabies incognito. Rubbing the infested animal's eartip may elicit scratching movements of the hindlimb; thispinna-pedal reflex suggests scabies.2.33.52-54

792 The Compendium • Small Animal

Figure 3A Figure 38

Figure 3-(A) Adult-onset demodicosis in a six-year-old intact male Scottish terrier with atopy. Extreme pyoderma and self-mutilationare evident. (8) The same dog after six weekly amitraz (0.05%) treatments. three weeks of oxacillin sodium therapy. and fatty acidsupplementation.

Figure 4A Figure 48

Figure 4-(A) Demodex cat; mite (30 /-1m x 200 /-1m) from a 14-year-old neutered tomcat with feline immunodeficiency virus infection.Compare its length and width with the length and width of the canine mite in Figure 1. (x60) (8) Appearance of the host's lesions.

Multiple deep skin scrapings from scattered reddenedcrusty areas may reveal mites or eggs. To obtain an ade­quate skin scraping, the clinician must scrape hairless ar­eas deeply enough for the area to ooze blood. In 35 % to50% of cases, no mites are found and diagnosis is based onhistory, clinical examination, and response to treatment. Ahistory of sudden-onset pruritus, exposure to a kennel orpet shop, or pruritus among humans in the household sug­gests scabies. 52 The mite is highly contagious by directcontact to other dogs; up to 50% of canine cases result inhuman disease. Humans evidence pruritic lesions on thearms, legs, and trunk. The canine parasite in humans isself-limiting and transient without reexposure. 2.4.11

TreatmentTreatment of infected dogs includes cleansing shampoos

to remove debris as well as systemic antibiotics and antiin­flammatory agents to treat infection and self-inflicted in­jury. Laundering the animal's bedding eliminates a sourceof reinfestation. Weekly malathion or phosmet dips havebeen suggested but may be ineffective because of resistantmites. Lime-sulfur dip (2.5%) is safe and effective; fivedips are given at five-day intervals. Lime sulfur is alsoantifungal, antibacterial, and antipruritic. 2.33 .52 Amitraz iseffective against Sarcoptes mites but has not been ap­proved for that use. A single application of amitraz(0.025 %) is effective in 98 % of cases. Some dogs requirea second or third application. 14.28.32.48.52

Extralabel use of oral or injected ivermectin (200 /-Ig/kg)is effective; a single treatment kills the mites. 11.14.28.35.52.55.56

Regardless of the method of treatment, all dogs in a house­hold must be treated.

The Compendium • Small Animal 793

TABLE IIIGeographic Distribution of Canine

and Feline Mites in the United States2,5,7-10

NOTOEDRES CATIClinical Manifestations

Notoedres cati is the mite of feline scabies. The mite issmaller than Sarcoptes mites and has a dorsal anus and evi­dent body striations (Figure 5 and Table I). Its life cycle issimilar to that of Sarcoptes mites. Notoedres cati is highlycontagious by direct contact and is present in large num­bers on the cat. All of the cats in a household or neighbor­hood may become infected. Although Notoedres mites arenot a common parasite of cats, enzootic feline populationscreate cluster outbreaks with high morbidity. 2.9.10.57

CLINICAL ,ign, include inten,. pm,itu, attribut­able to a hypersensitivity response to the burrowing femalemites as well as alopecia, crusting, and scaling of the face,ear tips, and distal extremities. Hyperpigmentation, lichen­ification, self-inflicted injury, and secondary skin infectioncan be severe (Figure 5). Young and chronically infectedcats become debilitated2,9.10,47 (Figure 6). Humans contact­ing infected cats can develop pruritic skin disease. Papules,crusts, and excoriations of the arms, legs, and trunk canoccur. The human disease is self-limiting and transientwithout reexposure.4.11 Dogs rarely become parasitized byNotoedres mites. 2,47

Skin scrapings of lesions reveal numerous mites andeggs (Figure 7). The mites are active and rapidly spreadover the cat's body. Diagnosis is usually easy.

°Extralabel use of ivermectin in dogs and cats kills these mites; ivermectinis contraindicated for collies and sheepdogs,

Arms, thighs, trunk

Legs, arms

Arms, legs, trunk, neck

Arms, trunk, neck

Human Anatomy Affected

Arms, trunk

Arms, forearms

Arms, chest

Mite

Cheyletiella species

Trombiculidae

Sarcoptes scabiei var. caniso

Notoedres catiO

Otodectes cynotisO

Lynxacarus radovskyio

Dermanyssus gallinaeo

TABLE IVZoonotic Mites of Dogs and Cats2,4,7,11-15

TreatmentTreatment includes cleansing shampoos to remove scales

and crusts. Antibiotics for secondary skin infection andcorticosteroids to treat pruritus and self-inflicted injurymay be needed. Four to six weekly dips with 2.5% limesulfur are safe and effective and alleviate pruritus. 2.9.11Amitraz dips (0.0125%) repeated at two-week intervals arereportedly effective, but this regimen is extralabel. II

Stronger amitraz dips (0.025%) have reportedly been ef­fective. 32 ,58 Malathion dip also is effective.2 All cats in thehousehold must be treated.

Extralabel use of ivermectin is highly effective againstNotoedres mites. I 1.33,59-61 I have treated an epizootic of No­toedres mange using subcutaneous ivermectin (300 llg/kg)on cats as young as four weeks. Over 200 cats have beentreated; most need only one ivermectin injection. No ad­verse effects have been apparent. 10

OTODECTES CYNOTISClinical Manifestations

Dogs and cats share the same ear mite species, Otodectescynotis. The mite is a large and mobile surface feeder (Ta­ble I). Transmission is by direct contact between pets; themite is not host specific. Otodectes cynotis mites have a21-day life cycle on the host; the life cycle features a dis­tinct stage involving deutonymphs. Deutonymphs are asexually undifferentiated stage and will be joined end toend by an adult male mite (Figure 8). If the deutonymphmolts to become a female, it will be fertilized. If a maledevelops or if a deutonymph fails to be joined by a male,no reproduction occurs. Ear mites have characteristic longlegs that extend beyond the body as well as short pedicelson these legs l.2,47 (Figure 8 and Table I).

Ear mites irritate the ear canal and hypersensitize thepet. The mite antigen induces antibody production soon af­ter the pet is parasitized,2 The result is pruritus; head shak­ing; and a heavy, dark, discolored wax discharge. Ear

Distribution

Rare; Hawaii, Puerto Rico,southern Florida

Throughout the United States

Throughout the United States

Uncommon; fields andwoodlands, especially in thecentral United States

Throughout the United States

Rare; bird nests, henhouses,pigeon coops

Throughout the United States

Uncommon; scatteredenzootic areas

Rare; throughout the UnitedStates

Mite

Sarcoptes scabiei var. canis

Notoedres cati

Pneumonyssoides caninum

Demodex species

Cheyletiella species

Trombiculidae

Dermanyssus gallinae

Otodectes cynotis

Lynxacarus radovskyi

794 The Compendium • Small Animal

Figure 5-Reactive skin from a cat with Notoedres cati infesta­tion. Hyperplasia, excessive keratinization, deeply burrowingmites, and inflammatory infiltrates are evident. (x 25)

Figure 7-Notoedres cati mite (length 200 J.(m). Body striationsare evident, as is the absence of a terminal anus. (x 78)

mites do not thrive in infected ears; patients with purulent.otitis are usually devoid of ear mites. The mites can leavethe ear canal and irritate the neck, head, rump, and tail. 2.9

Head shaking can induce aural hematomas, and earscratching can cause localized moist dermatitis and trau­matic skin excoriations. Humans can develop papules onthe arms and trunk; this condition is self-limiting withoutreexposure. 4.62 Diagnosis of Otodectes cynotis is by directvisualization or microscopic examination of a swab smear.

TreatmentMiticidal therapy is preceded by gentle cleansing of the

ear canals with a cerumenolytic agent, such as mineral oilor squalene. Such miticides as topical thiabendazole, ro­tenone in oil, or methylcarbaryI are all effective. Treat­ment intervals are staggered to increase kill of wanderingmites; periauricular areas can also be treated to kill anymobile mites. Because the mites are so contagious, all ani­mals in the household, kennel, or cattery should betreated. 2.47

Figure 6-A debilitated five-month-old male kitten. Notoedrescati infestation over its whole body responded well to ivermec­tin (300 J.(g/kg) and supportive care.

Figure 8-Adult male Otodectes cynotis mite attached to adeutonymph. Fertilization will occur if the deutonymph developsinto a female mite. The male measures 250 J.(m x 300 J.(m.Eight long legs and short pedicels are evident. (x60)

EXTRALABEL use of ;venneclin (;njectinn of 200 In400 J.(g/kg) can successfully eliminate Otodectes cynotismites in dogs and cats. Ivermectin may be the ideal remedyfor chronic infestations in a kennel or cattery. 4.55.63 Extrala­bel use of amitraz (0.05% on the body and 0.5% dilutedwith 50% propylene glycol in the ear canals) is reportedlyeffective against Otodectes cynotisY Amitraz at a concen­tration of 0.025 % is also effective.48

LYNXACARUS RADOVSKYIClinical Manifestations

Lynxacarus radovskyi is the cat fur mite. It is a largehair-clasping surface feeder that can be easily seen througha head loupe (Table I). The mite has modified sternalplates that allow it to clasp a hair and travel along hairshafts over the eat's body I (Figure 9).

Figure 9A

Figure 98

Although Lynxacarus radovskyi is not common through­out the United States, it is enzootic in a few areas (TableIII).6.7.63-66 The mite has an affinity for the tail tip, tailhead,

The Compendium • Small Animal 795

Figure 9C

Figure 9-(A) Female Lynxacarus radovskyi mite measuring500 JAm long. Modified sternal plates enclose the eat's hair. Thefirst pair of legs moves the mite along the hair. (x60) (8) Malemite 430 JAm long. (x60) (C) Fur mite eggs measuring approxi­mately 200 JAm long attached to the eat's hair. (x60)

and perineum. When this parasite is present in large num­bers, the haircoat can feel granular and appear peppered.Small populations of fur mites cause no clinical signs; butheavily parasitized cats have pruritus, regional alopecia,and areas of shortened fur and develop a dry, rust-coloredcoat with such secondary signs as gingivitis or hair balls. 7

The mite is contagious to cats and humans by direct con­tact. One of my clients had a papular forearm rash thatresolved when her heavily parasitized cat was cleansed.Diagnosis is swiftly made by plucking suspect hairs to re­veal the mite or attached eggs (Figure 9).

TreatmentTreatment is easily accomplished using 2.5 % lime-sulfur

dips or pyrethrin shampoos, powders, or sprays.25 Flea

796 The Compendium • Small Animal

Figure 10A

Figure 10C

Figure 10-(A) This two-year-old male English bulldog has nasaldischarge and pruritic facial irritation resulting from Pneumonys­soides caninum infestation. (8) A typical Pneumonyssoidescaninum mite embedded in dried nasal exudate from the dog.(C) A long-legged nasal mite found wandering on the dog'smuzzle. (x60)

Figure 108

collars do not work. House cats should be separated fromferal cats to prevent reinfestation. 7 Subcutaneous ivermec­tin (300 j.Lg/kg) has been effective in killing Lynxacarusradovskyi in an ongoing epizootic I am treating,

PNEUMONYSSOIDES CANINUMClinical Manifestations

Pneumonyssoides caninum is the nasal or sinus mite ofdogs. As with the previously mentioned cat fur mite, littleis known about the complete life cycle of Pneumonyssoidescaninum. Like fur mite infestation, Pneumonyssoidescaninum infestation responds favorably to treatment. Thesheltered habitat of the nasal sinus mite, however, protectsit from injury and investigation, Larval and adult stagesare usually seen, and the female may be ovoviviparous,The mode of contagion is unknown but is probably directcontact. The mite may cause no signs; however, rhinitis,serous nasal discharge, facial pruritus, sneezing, nocturnalrestlessness, stertorous breathing sounds, and orbital infec­tion have been reported, The mite has reportedly beenfound in lung, liver, and perirenal tissue8.68 (Figure 10).

Diagnosis is made by finding the long-legged mitecrawling on the dog's muzzle, in nasal discharge, or in thenasal passages (observed by rhinoscopy). The mite couldbe confused with Dermanyssus mites or larval ticks,

TreatmentThe mite can be killed by ivermectin injections (200 j.Lg/

kg); two doses three weeks apart is an effective regimen. 8

Before this extralabel use of ivermectin was made, thera­pies for nasal sinus mite infestations included ether, ro­tenone, cresol, and organophosphates administered by na­sal drops, inhaler bags, or insecticide strips,68.69

DERMANYSSUS GALLINAEClinical Manifestations

The red poultry mite, Dermanyssus gallinae, infestsdogs, cats, and humans contacting infested bird nests,

798 The Compendium • Small Animal

henhouses, or pigeon COOpS.2.70.15 The eight-legged nymphand adult stages are parasitic. The mite has long anteriorlegs. It tends to infest the back and legs of pets. Pruritus,papules, crusts, and erythema can be present. The mite isdiagnosed by skin scrapings.

TreatmentTreatment is accomplished with lime sulfur, pyrethrins,

or any safe acaricide. Ivermectin injections are effective inkilling Dermanyssus gallinae on poultry71; ivermectin maybe as effective when used in the rare canine and felinecases of infestation. Avoidance of the source of the para­sites or treatment of the source prevents reinfestation.

CONCLUSIONParasitic mite infestations of dogs and cats can be diffi­

cult or impossible to cure. Inherited factors, the contagiousnature of the parasites, and their zoonotic potential compli­cate the management of these parasites. Because extralabelor nonapproved use of therapeutics may be necessary,owner awareness and cooperation are critical. Milbemy­cin, which has recently been approved for use in theUnited States, might someday be used to treat parasitismthat is resistant to ivermectin or that has occurred in ani­mals unable to tolerate ivermectin.

About the AuthorDr. Foley is affiliated with the Upper Keys Veterinary Clinic lo­cated in Islamorada. Florida.

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