Parasitic Mites of Dogs and Cats

Transcription

~......OMPENDIUM
A REPRINT FROM
...........NTlNUING
UCATION
. .',
.'.
"~OR
SPECIAL
FOCUS
ON
THE PRACTICING VETERINARIAN
PARASITOLOGY
Continuing Education Article #5
.. :; Vol.
13; .No,
~. M~y 19,.91 783
Parasitic Mites of Dogs and Cats
KEY 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
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 the
parasite 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.
to
Upper Keys Veterinary Clinic
Islamorada. 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 for
chiggers (Trombiculidae), of which only the larval stage is
parasitic, mites of all four stages are parasitic.
The three suborders of mites in the order Arachina consist of animals of diverse sizes, shapes, and distinguishing
characteristics (Table I). The host anatomic areas preferred
by 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 the
j. "':":_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 contract
Demodex canis mites by direct and close contact with a
heavily parasitized carrier. 18
The presence of Demodex canis mites is considered to be
a disease state when excessive numbers of mites of all four
stages of the life cycle are present in a skin scraping from
an animal with clinical signs. 19 Demodicosis is also termed
follicular, red, pulJPY, squamous, pilosebaceous, or Acarus mange. Demodex mites reproduce and lay eggs in the
hair follicle and associated sebaceous and apocrine sweat
glands. The mites puncture cells and ingest the cell contents; this feeding activity produces keratinization that
plugs 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 deA 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 most
mite (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 pruriwith the dam during the first two to three days of life. 17
tus, erythema, and bacterial infection. The mites may
Mites 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)1
Class Arachnida: Head, thorax, and abdomen
are fused. Mouthparts in capitulum; antennae
and mandibles missing. Six-legged larvae,
eight-legged nymph and adult stages.
Order Arachina
Suborder Prostigmata
Family Demodicidae
Demodex canis
Demodex cati
Unnamed Demodex species
Family Cheyletiellidae
Cheyletiella yasguri
Cheyletiella blakei
Family Trombiculidae
Walchia americana
Trombicula alfreduggesi
Trombicula autumnalis
Suborder Astigma: Respiratory pores
absent; respiration occurs through
integument
Family Sarcoptidae
Sarcoptes scabiei var. canis
Notoedres cati
Family Psoroptidae
Otodectes cynotis
Subfamily Listrophoroidea
Lynxacarus radovskyi
Suborder Mesostigmata: Respiratory pores
on mid body
Family Halarachnidae
Pneumonyssoides caninum
Family Dermanyssidae
Dermanyssus gallinae
Suborder Metastigmata: Ticks
follicles on the margin of lesions may be needed.
Skin scraping suffices to diagnose localized or generalized demodicosis; whereas in cases of pododermatitis, skin
biopsy sometimes is necessary to establish a diagnosis. Localized demodicosis is most common in intact purebred
dogs (76 %) younger than one year of age. 18 Ninety percent
of cases of localized mange resolve spontaneously in four
to eight weeks. Underlying transient stresses (e.g., adolescence, estrus, endoparasites, growth, nutrition, vaccination, surgery, and pregnancy) have been incriminated and
may contribute to the disease. Sex, haircoat length, sebaceous gland size, and hypothyroidism do not appear to be
factors in the development of localized demodicosis.'8.19.21
Ten percent of dogs with the localized form deteriorate to
generalized juvenile demodicosis. The generalized form in-
volves large areas of the body and causes alopecia (in more
than 10 areas), erythema, and varying degrees of crusting,
follicular plugging, and hemorrhage. A rancid seborrheic
odor, folliculitis, furunculosis, cellulitis, deep pyoderma,
pruritus, and peripheral lymphadenopathy often accompany
generalized juvenile demodicosis. The condition can also
occur without major associated reactions2.'7-'9.22 (Figure 2).
In one study of 821 dogs with generalized juvenile
mange, 87 % of the cases occurred in animals older than
seven months of age; most of the subjects were intact purebreds (80%). Age and familial predisposition were the
most important factors. 18 Two mechanisms have been proposed to explain the inherited immunologic predisposition
to generalized juvenile demodicosis. The first explanation
is that a genetic immune abnormality allows massive mite
proliferation. The heavy mite population induces a humoral substance (B-cell stimulation) that in turn suppresses
cell-mediated (T-cell) immunity. Treatment is directed at
elimination of the mites to restore T-cell function. 23 -25
The second proposed mechanism is that genetic predisposition to pyoderma complicates the generalized juvenile
demodicosis and suppresses lymphocyte blastogenesis (B
and T cells). The pyoderma suppresses serum lymphocyte
immunoregulatory factors in proportion to the degree of
infection. Therapy would therefore be directed at the skin
infection. 22 Immunosuppressive agents, such as corticosteroids, should not be used in animals with generalized
juvenile demodicosis. Because of the inherited predisposition to the condition, the American Academy of Veterinary
Dermatology recommends that dogs with generalized demodicosis should be sterilized.26
Demodectic pododermatitis tends to be a chronic digital
and interdigital disease often complicated by pyoderma.
Certain breeds are at increased risk (see the listing on Canine Breeds Predisposed to Demodicosis). Biopsy may be
necessary to reveal the mites. In many cases, the condition
is never cured. 2.27
Adult-onset demodicosis may not be hereditary. Most
cases are secondary to iatrogenic Cushing's syndrome, atopy, immune deficiencies, diabetes mellitus, heartworms,
malignancies, use of immunosuppressive agents, or deep
pyoderma. Patients with the adult-onset disorder must be
thoroughly examined and checked for other parasites and
disease processes. A complete blood count, blood profile,
and endocrine screening should be performed to identify
any inciting factors needing treatment. Scottish terriers and
West Highland white terriers seem particularly prone to
adult-onset demodicosis complicated with atopy and deep
pyoderma (Figure 3). Adult-onset generalized demodicosis
can necessitate euthanasia. 2.27-29
Treatment of Canine Demodicosis
Therapy for canine demodicosis depends on its form and
complications. Localized demodicosis has a good prognosis; 90% of cases remit spontaneously within four to eight
The Compendium • Small Animal 785
weeks without treatment. If the patient's owner insists on
some 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 and
individualized therapy is indicated. From 30% to 50% of
generalized juvenile demodicosis cases resolve spontaneously. Acaricidal therapy may not be necessary immediately; the clinician should monitor the patient's progress
closely. Skin scrapings performed at two- to four-week intervals indicate when increasing mite population and predominance of immature forms dictate more-aggressive
treatment. Review of the animal's pedigree could reveal
the likelihood of spontaneous remission.2.17-19
Treatment of generalized demodicosis (juvenile and
adult-onset) should be directed at simultaneous elimination
of mites and any underlying pyoderma. Currently, amitraz
is the only agent approved for use as a Demodex miticide
in the United States. The manufacturer advises that 10.6
ml 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 be
shaved and cleansed with a follicular flushing shampoo or
a therapeutic shampoo (e.g., with povidone-iodine or
chlorhexidine). Areas of deep pyoderma and furuncles
should be avoided during dipping to minimize toxicity associated with amitraz absorbance. 27
Extralabel use of amitraz dramatically improves cure
rates; an animal is considered cured if skin scrapings are
negative 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 cure
rate for generalized demodicosis can rise from 20% to
75 %. Halving the diluent (6 ml amitraz in 1 gallon of water) to double the dose to 0.06 % can raise the cure rate up
to 80 % with minimal toxicity. Amitraz toxicity is manifested as increased sleepiness, depression, and anorexia
during the first 24 hours after treatment. More-extreme
signs 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 special
caution for diabetic animals. 31 Humans with diabetes must
wear gloves when applying amitraz. Weekly administration of 0.05% amitraz seems most efficacious; but pet
owners must be advised that this regimen is extralabel. 30
In France, amitraz concentrations of 0.05% and 0.10%
have reportedly been effective and produced no toxic side
effects. 32 Also in France, an amitraz-impregnated collar is
marketed for Demodex and tick control,32 Treatment failures may be related to premature cessation of treatment or
failure to correct underlying stress or infection. Months of
weekly dipping may be needed to effect a cure; there is no
prescribed number of dips.
Extralabel use of ronnel can be tried to treat generalized
juvenile demodicosis if amitraz fails. Ronnel is mixed as a
4% solution with propylene glycol (Scott's formula).24 The
agent can be dispensed in a 4-ounce childproof amber medicine bottle containing 18 ml of 33.3 % ronnel solution plus
100 ml of propylene glycol. The preparation is stable for
about one month. One third of the dog's body is painted
daily so that each area is treated once every three days in
sequence. Ronnel is effective in 90% of cases but is irritating to the skin and highly toxic to animals and humans. 19
Dogs to be treated with ronnel (or any organophosphate)
should be free of heartworm infection before treatment is
initiated. Demodex canis is resistant to ectoparasiticides
less potent than ronnel.
D
EMODECTIC pododennalitis can he "eated with
weekly immersion in double-strength amitraz (0.05%) or
4 % topical ronnel. Fresh daily amitraz can be applied (l
ml 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 of
trichlorfon is also extralabel.
For all miticidal therapies, skin scrapings must be monitored at two- to four-week intervals. Counts or estimates of
the numbers of live and dead mites should be made and
therapy continued for three to four weeks after scrapings
are negative. Recurrence is possible, and lifelong amitraz
dips 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 seriously
changes the prognosis because it can cause fatal septicemia. 18 An antibiotic, such as erythromycin, lincomycin,
oxacillin sodium, cephalosporin, or chloramphenicol, may
be 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's
infected skin.
Vitamin E (up to 400 U orally twice a day) and fatty acid
supplements may quell skin inflammation in dogs with
generalized demodicosis and are useful for treating any underlying atopy. 33 Immune stimulants, such as levamisole or
injectable bacterins, have not been successful against mites
786 The Compendium. Small Animal
TABLE I
Size and Identifying Characteristics of Parasitic Mites of Dogs and Cats2-6
Mite
Size of Adult Female
(lAm)
Characteristics
Demodex canis
40 x 225
Spindle-shaped eggs; elongated body,
striations
Demodex cati
30 x 200
Oval eggs; smaller and slimmer body
than Demodex canis
Unnamed Demodex species
30 x 110
Short, blunt abdomen; superficial skin
parasite
Cheyletiella yasguri
265 x 500
Cone-shaped sensory organ
Cheyletiella blakei
265 x 500
Huge mouthhooks, heart-shaped sensory
organ; surface mite
Trombiculidae (chiggers)
210 x 400
250 x 400
Terminal anus; long, unsegmented
pedicel
Notoedres cati
200 x 240
Dorsal anus, body striations
Otodectes cynotis
300 x 400
Long legs, short pedicel; males have
pretarse on all four pairs of legs; surface
mite
250 x 515
Hair-clasping sternal plates, elongated
body; surface mite
150 x 400
Long legs, small palps; often confused
with Dermanyssus mites
150 x 400
Long legs, stocky palps; deeply
embedded, red poultry mites; surface
mites
but may aid pyodenna therapy. 23.28
The extralabel use of ivennectin has produced disappointing results against Demodex mites, although it is
highly effective against other mites. 34 ,35 Ivennectin paralyzes susceptible mites by potentiating the neuroinhibitor
v-aminobutyric acid (GABA), thus blocking postsynaptic
neuromuscular potentials, and is lethal to the parasite.
Ivennectin does not cross mammalian blood-brain barriers
to reach the GABA receptors. 35 Ivennectin can cause potentially fatal idiosyncratic reactions in collies, sheepdogs,
and related crossbreeds and should not be used in these
animals. 36 . 37 Dogs should be screened for heartwonn infection before receiving ivennectin therapy; the precise
weight of all animals, dogs or cats, should be measured to
detennine the correct dose.
A 1% preparation of ivennectin provides 10 mg/ml
(10,000 Ilg/ml). In one study, two 400-llg/kg injections of
ivennectin given two weeks apart were effective against
Demodex canis. 38 Another trial of the same dose at weekly
intervals did not resolve the infestation but seemed to pro-
. Orange-red, six-legged parasitic larva;
hairy body; surface mite
vide some reduction of clinical signs. 34 The efficacy of
milbemycin oxime against Demodex canis is under study.
Clinical Manifestations in Cats
Feline demodicosis is caused by the follicular mite Demodex catil. 2 •9 (Figure 4) and a much less common unnamed
Demodex species, which is found only in the stratum corneum of the cat's skin. 39 •4O The size and shapes of these
mites differ from those of Demodex canis 3 (Table I). Both
species are rare. Feline demodicosis manifests itself in two
fonns. The localized fonn exhibits erythematous patches
of alopecia along with scaling and crusting of the eyelids,
face, chin, or neck (Figure 4). Ceruminous otitis may be
seen. Multiple skin scrapings disclose the parasite. Spontaneous remission can occur. Generalized feline demodicosis
is usually associated with an underlying disease (e.g., diabetes mellitus, hyperadrenocorticism, endocrine alopecia,
feline leukemia virus infection, feline immunodeficiency
virus, or an autoimmune disease).41-44
Generalized feline demodicosis may be more common in
Figure 1A
Figure 18
Figure 1-(A) Characteristic Demodex canis mite measuring 40 /-1m x 225 /-1m. (x60) (8) Demodex canis egg. (x60)
CHEYLETIELLA SPECIES
Clinical Manifestations
Figure 2-A 10-month-old female akita with generalized juvenile
demodicosis. Pyoderma was minimal relative to the extent of
Demodex 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, and
trunk. Eosinophilia and pyoderma may occur. Intense
pruritus can occur with infestations of the unnamed Demodex species. 3
Treatment of Feline Demodicosis
The prognosis for treatment of feline demodicosis is
good. Treatments include 2.5% lime-sulfur dips, carbaryl
shampoos, and malathion dips.2.42 Carbamate products,
however, are not approved for use on kittens or nursing
puppies. Organophosphates should only be used cautiously
in 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 be
treated with miticides other than amitraz. 31
Cheyletiella yasguri of dogs and Cheyletiella blakei of
cats are large, surface-feeding mites that live in keratin
(Table I). Their 35-day life cycle is spent entirely on the
dog or cat. The mite has enormous hooked mouthparts and
combed legs; it attaches its eggs to hair. The mites are very
mobile and contagious by direct contact; the so-called
walking dandruff can spread rapidly through a kennel or
cattery. Puppies and kittens are most susceptible.
Cheyletiella mites are not host specific, and a reference
text is advisable for correct identification of the species.
The hallmark of Cheyletiella is the moving white flakes
along the dorsal midline and head of the dog and cat.
Scraping, combing, or applying transparent adhesive tape
to the suspect areas aids in disclosing the large, visible
mites. Magnifying loupes and selective removal of questionable flakes or hairs represent the quickest method.
Some fastidious cats may require skin scrapings or fecal
flotations to reveal mites. 2.4.9.46.47
Dogs experience more pruritus associated with cheyletiellosis than do cats. The canine disease may resemble
seborrhea oleosa or fleabite dermatitis. Affected dogs have
scaly, oily skin. Cats may appear to have seborrhea sicca
with scales and red scabs, or they may show no signs at
all. Humans, especially cattery personnel, are highly susceptible to Cheyletiella infestation. Pruritus, erythematous
papules, and pustules appear on the chest, arms, thighs,
and abdomen. The human disease is transient (three
weeks) without reexposure.4.11-13
Treatment
Treatment of Cheyletiella mite infestation can be accomplished by using lime-sulfur dips, carbaryl shampoo or 5 %
dust, 0.5 % malathion dips, or pyrethrins weekly for four
or five treatments.2.9 Although amitraz has not been approved for use against Cheyletiella, this agent is effective
TABLE II
Host Anatomic Areas Preferred by
Canine and Feline Mites2,7,8
Mite
Preferred Location on Host
Demodex species
Localized: follicles of face,
skull, ear canal, forelegs;
Generalized: anywhere and
everywhere
Cheyletiella species
Surface of dorsal midline
Trombiculidae
Surface of head, legs, and
ventral areas
Epidermis of ear tips, elbows,
and glabrous areas
Notoedres cati
Epidermis of ears, face, and
feet
Otodectes cynotis
Surface of ear canals and
periauricular areas
Surface of perineum, tailhead,
and tail tip
Nasal sinus, nasal passages
Surface of legs and back
Canine Breeds Predisposed
to Demodicosis
2
,5.18,19
Generalized Juvenile Demodicosis
Afghan hound, beagle, Boston terrier, boxer,
Chihuahua, Chinese shar peL chow chow,
collie, dalmatian, dachshund, Doberman
pinscher, English bulldog, German shepherd,
Great Dane, Old English sheepdog, pointer,
pit bullterrier, pug, Staffordshire bullterrier
Chronic Demodectic Pododermatitis
Great Dane, Newfoundland, Old English
sheepdog, Saint Bernard
Generalized Adult-Onset Demodicosis
Cocker 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
SARCOPTES
on dogs (0.025%); one treatment is sufficient. 48 Subcutaneous ivermectin (300 J.lg/kg) repeated after a five-week
interval is effective and useful for miticide-resistant cases
and may be ideal for cattery and kennel infestations. 14 ,49
Regardless of the treatment used against Cheyletiella, all of
the animals in the household or facility must be treated.
TROMBICULIDAE
Trombiculiasis is infestation by parasitic, six-legged, larval chiggers. Dogs, cats, and humans can be parasitized by
20 of the more than 700 species of chiggers. Infestation is
most prevalent during the late summer and fall and in animals frequenting fields or woodlands where the larval
mites are contracted directly (Table III). The nymphs and
adult chiggers are free-living and not parasitic. The bright
orange-red mites are surface feeders; their salivary secretions induce intense pruritus that lasts longer than the mites
are present on the body. Alopecia, pustules, and scaling of
the head, ears, ventral trunk, legs, and paws can occur.
The entire body can be afflicted; self-inflicted injury is often a problem.
Diagnosis and Treatment
Diagnosis can be made by scraping the mite from the
lesion, but the mite may already have detached from the
animal.2· 5.9,47.5o.51 Thus, chigger infestations might be more
common than they are believed to be. Mites that are present
Scabies caused by the mite Sarcoptes scabiei var. canis is
often misdiagnosed as contact allergy, food allergy, atopy,
or fleabite dermatitis. Many pruritus-producing skin diseases can resemble scabies. 52 This mite usually appears on
dogs, occurs only rarely in cats,53.54 and spends its 17- to
21-day life cycle in epidermal pockets. The large female
mite lays three to five eggs per day in freshly burrowed
tunnels (Table I). The male mite, along with mites in the
larval and nymph stages, lives in vacated burrows. The
male 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 mite
targets the pinnae, elbows, back, chest, abdomen, or hairless areas. The entire body can be affected. Alopecia, hemorrhagic crusts, and papules are worsened by self-inflicted
injury. The skin becomes Iichenified, and secondary infection and lymphadenopathy occur. The animal can become
debilitated; but well-nourished, well-groomed dogs also
can have scabies. Frequent grooming of dogs and frequent
insecticidal shampooing can cause and mask scabies in
some pampered pets; the resultant condition has been
called scabies incognito. Rubbing the infested animal's ear
tip may elicit scratching movements of the hindlimb; this
pinna-pedal reflex suggests scabies.2.33.52-54
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-mutilation
are evident. (8) The same dog after six weekly amitraz (0.05%) treatments. three weeks of oxacillin sodium therapy. and fatty acid
supplementation.
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 reddened
crusty 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 % to
50% of cases, no mites are found and diagnosis is based on
history, clinical examination, and response to treatment. A
history of sudden-onset pruritus, exposure to a kennel or
pet shop, or pruritus among humans in the household suggests scabies. 52 The mite is highly contagious by direct
contact to other dogs; up to 50% of canine cases result in
human disease. Humans evidence pruritic lesions on the
arms, legs, and trunk. The canine parasite in humans is
self-limiting and transient without reexposure. 2 .4.11
Treatment
Treatment 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 source
of reinfestation. Weekly malathion or phosmet dips have
been suggested but may be ineffective because of resistant
mites. Lime-sulfur dip (2.5%) is safe and effective; five
dips are given at five-day intervals. Lime sulfur is also
antifungal, antibacterial, and antipruritic. 2 . 33 .52 Amitraz is
effective 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 require
a 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.
TABLE III
Geographic Distribution of Canine
and Feline Mites in the United States2 ,5,7-10
TABLE IV
Zoonotic Mites of Dogs and Cats2,4,7,11-15
Mite
Mite
Distribution
Demodex species
Throughout the United States
Trombiculidae
Uncommon; fields and
woodlands, especially in the
central United States
Human Anatomy Affected
Arms, thighs, trunk
Trombiculidae
Legs, arms
Sarcoptes scabiei var. caniso
Arms, legs, trunk, neck
Notoedres catiO
Arms, trunk, neck
Otodectes cynotisO
Arms, trunk
Lynxacarus radovskyio
Arms, forearms
Notoedres cati
Uncommon; scattered
enzootic areas
Dermanyssus gallinaeo
Arms, chest
Otodectes cynotis
Rare; Hawaii, Puerto Rico,
southern Florida
Rare; throughout the United
States
Rare; bird nests, henhouses,
pigeon coops
NOTOEDRES CATI
Notoedres cati is the mite of feline scabies. The mite is
smaller than Sarcoptes mites and has a dorsal anus and evident body striations (Figure 5 and Table I). Its life cycle is
similar to that of Sarcoptes mites. Notoedres cati is highly
contagious 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 are
not a common parasite of cats, enzootic feline populations
create cluster outbreaks with high morbidity. 2.9.10.57
CLINICAL ,ign, include inten,. pm,itu, attributable to a hypersensitivity response to the burrowing female
mites as well as alopecia, crusting, and scaling of the face,
ear tips, and distal extremities. Hyperpigmentation, lichenification, self-inflicted injury, and secondary skin infection
can be severe (Figure 5). Young and chronically infected
cats become debilitated 2,9.10,47 (Figure 6). Humans contacting infected cats can develop pruritic skin disease. Papules,
crusts, and excoriations of the arms, legs, and trunk can
occur. The human disease is self-limiting and transient
without reexposure. 4.11 Dogs rarely become parasitized by
Notoedres mites. 2,47
Skin scrapings of lesions reveal numerous mites and
eggs (Figure 7). The mites are active and rapidly spread
over the cat's body. Diagnosis is usually easy.
°Extralabel use of ivermectin in dogs and cats kills these mites; ivermectin
is contraindicated for collies and sheepdogs,
Treatment
Treatment includes cleansing shampoos to remove scales
and crusts. Antibiotics for secondary skin infection and
corticosteroids to treat pruritus and self-inflicted injury
may be needed. Four to six weekly dips with 2.5% lime
sulfur are safe and effective and alleviate pruritus. 2.9.11
Amitraz dips (0.0125%) repeated at two-week intervals are
reportedly 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 the
household must be treated.
Extralabel use of ivermectin is highly effective against
Notoedres 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 been
treated; most need only one ivermectin injection. No adverse effects have been apparent. 10
OTODECTES CYNOTIS
Dogs and cats share the same ear mite species, Otodectes
cynotis. The mite is a large and mobile surface feeder (Table I). Transmission is by direct contact between pets; the
mite is not host specific. Otodectes cynotis mites have a
21-day life cycle on the host; the life cycle features a distinct stage involving deutonymphs. Deutonymphs are a
sexually undifferentiated stage and will be joined end to
end by an adult male mite (Figure 8). If the deutonymph
molts to become a female, it will be fertilized. If a male
develops or if a deutonymph fails to be joined by a male,
no reproduction occurs. Ear mites have characteristic long
legs that extend beyond the body as well as short pedicels
on these legs l.2,47 (Figure 8 and Table I).
Ear mites irritate the ear canal and hypersensitize the
pet. 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
Figure 5-Reactive skin from a cat with Notoedres cati infestation. Hyperplasia, excessive keratinization, deeply burrowing
mites, and inflammatory infiltrates are evident. (x 25)
Figure 7-Notoedres cati mite (length 200 J.(m). Body striations
are 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 leave
the ear canal and irritate the neck, head, rump, and tail. 2.9
Head shaking can induce aural hematomas, and ear
scratching can cause localized moist dermatitis and traumatic skin excoriations. Humans can develop papules on
the arms and trunk; this condition is self-limiting without
reexposure. 4 .62 Diagnosis of Otodectes cynotis is by direct
visualization or microscopic examination of a swab smear.
Treatment
Miticidal therapy is preceded by gentle cleansing of the
ear canals with a cerumenolytic agent, such as mineral oil
or squalene. Such miticides as topical thiabendazole, rotenone in oil, or methylcarbaryI are all effective. Treatment intervals are staggered to increase kill of wandering
mites; periauricular areas can also be treated to kill any
mobile mites. Because the mites are so contagious, all animals in the household, kennel, or cattery should be
treated. 2.47
Figure 6-A debilitated five-month-old male kitten. Notoedres
cati 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 a
deutonymph. Fertilization will occur if the deutonymph develops
into a female mite. The male measures 250 J.(m x 300 J.(m.
Eight long legs and short pedicels are evident. (x60)
E
XTRALABEL use of ;venneclin (;njectinn of 200 In
400 J.(g/kg) can successfully eliminate Otodectes cynotis
mites in dogs and cats. Ivermectin may be the ideal remedy
for chronic infestations in a kennel or cattery. 4.55.63 Extralabel use of amitraz (0.05% on the body and 0.5% diluted
with 50% propylene glycol in the ear canals) is reportedly
effective against Otodectes cynotisY Amitraz at a concentration of 0.025 % is also effective. 48
LYNXACARUS RADOVSKYI
Lynxacarus radovskyi is the cat fur mite. It is a large
hair-clasping surface feeder that can be easily seen through
a head loupe (Table I). The mite has modified sternal
plates that allow it to clasp a hair and travel along hair
shafts over the eat's body I (Figure 9).
Figure 9A
Figure 9C
Figure 9-(A) Female Lynxacarus radovskyi mite measuring
500 JAm long. Modified sternal plates enclose the eat's hair. The
first pair of legs moves the mite along the hair. (x60) (8) Male
mite 430 JAm long. (x60) (C) Fur mite eggs measuring approximately 200 JAm long attached to the eat's hair. (x60)
Figure 98
Although Lynxacarus radovskyi is not common throughout the United States, it is enzootic in a few areas (Table
III).6.7.63-66 The mite has an affinity for the tail tip, tailhead,
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; but
heavily parasitized cats have pruritus, regional alopecia,
and areas of shortened fur and develop a dry, rust-colored
coat 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 that
resolved when her heavily parasitized cat was cleansed.
Diagnosis is swiftly made by plucking suspect hairs to reveal the mite or attached eggs (Figure 9).
Treatment
Treatment is easily accomplished using 2.5 % lime-sulfur
dips or pyrethrin shampoos, powders, or sprays.25 Flea
Figure 10A
Figure 108
collars do not work. House cats should be separated from
feral cats to prevent reinfestation. 7 Subcutaneous ivermectin (300 j.Lg/kg) has been effective in killing Lynxacarus
radovskyi in an ongoing epizootic I am treating,
PNEUMONYSSOIDES CANINUM
Pneumonyssoides caninum is the nasal or sinus mite of
dogs. As with the previously mentioned cat fur mite, little
is known about the complete life cycle of Pneumonyssoides
caninum. Like fur mite infestation, Pneumonyssoides
caninum infestation responds favorably to treatment. The
sheltered habitat of the nasal sinus mite, however, protects
it from injury and investigation, Larval and adult stages
are usually seen, and the female may be ovoviviparous,
The mode of contagion is unknown but is probably direct
contact. The mite may cause no signs; however, rhinitis,
serous nasal discharge, facial pruritus, sneezing, nocturnal
restlessness, stertorous breathing sounds, and orbital infection have been reported, The mite has reportedly been
found in lung, liver, and perirenal tissue8.68 (Figure 10).
Diagnosis is made by finding the long-legged mite
crawling on the dog's muzzle, in nasal discharge, or in the
nasal passages (observed by rhinoscopy). The mite could
be confused with Dermanyssus mites or larval ticks,
Treatment
Figure 10C
Figure 10-(A) This two-year-old male English bulldog has nasal
discharge and pruritic facial irritation resulting from Pneumonyssoides caninum infestation. (8) A typical Pneumonyssoides
caninum mite embedded in dried nasal exudate from the dog.
(C) A long-legged nasal mite found wandering on the dog's
muzzle. (x60)
The 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 GALLINAE
The red poultry mite, Dermanyssus gallinae, infests
dogs, cats, and humans contacting infested bird nests,
henhouses, or pigeon COOpS.2.70.15 The eight-legged nymph
and adult stages are parasitic. The mite has long anterior
legs. It tends to infest the back and legs of pets. Pruritus,
papules, crusts, and erythema can be present. The mite is
diagnosed by skin scrapings.
Treatment
Treatment is accomplished with lime sulfur, pyrethrins,
or any safe acaricide. Ivermectin injections are effective in
killing Dermanyssus gallinae on poultry71; ivermectin may
be as effective when used in the rare canine and feline
cases of infestation. Avoidance of the source of the parasites or treatment of the source prevents reinfestation.
CONCLUSION
Parasitic mite infestations of dogs and cats can be difficult or impossible to cure. Inherited factors, the contagious
nature of the parasites, and their zoonotic potential complicate the management of these parasites. Because extralabel
or nonapproved use of therapeutics may be necessary,
owner awareness and cooperation are critical. Milbemycin, which has recently been approved for use in the
United States, might someday be used to treat parasitism
that is resistant to ivermectin or that has occurred in animals unable to tolerate ivermectin.
About the Author
Dr. Foley is affiliated with the Upper Keys Veterinary Clinic located in Islamorada. Florida.
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Parasitic Mites of Dogs and Cats

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