Full text of DOI:10.1111/j.1751-0813.2000.tb11742.x

Clinical
Treatment of canine adult-onset demodicosis
SE SHAW and AP FOSTER
Department of Clinical Veterinary Science, University of Bristol, Langford House, BS40 5DU, UK
This is used in combination with topical 2% chlorhexidine or
10% ethyl lactate-based shampoos. Benzoyl peroxide shampoos
are not used in our cases as they have been associated with
potentiation of pruritus.
emodicosis can present in a variety of clinical patterns
including adult-onset generalised demodicosis with
Dbacterial pyoderma. The latter is the most common
pattern seen in dogs presented to our dermatology service.
The onset of demodicosis in dogs over three years of age has
been associated with a number of underlying diseases that
apparently deregulate the commensal relationship between
parasite and host. The treatment protocol and overall prognosis
for demodicosis in these cases is dependent to a large extent on
the prognosis for the underlying disease. Concurrent underlying
trigger factors reported for adult-onset demodicosis include
neoplasia, spontaneous or iatrogenic hyperadrenocorticism,
hypothyroidism and immunosuppressive therapy.1,2 Unlike
juvenile-onset demodicosis, a familial or breed disposition is not
reported.
In a study of 25 cases of adult-onset demodicosis (unpub-
lished) all were pure-bred dogs and 15 were small terriers,
predominantly West Highland White Terriers (six) and Shih
Tzus (four). The terrier breeds were overrepresented when
compared to the British pure-bred dog population and the
hospital dog population. Most (84%) of the affected dogs had
more than one risk factor for generalised demodicosis: 21 cases
had received a systemic glucocorticoid for four weeks or longer
for existing skin disease, including allergy and pemphigus foli-
aceus, and of these, six were classified as having iatrogenic
hyperadrenocorticism. Five dogs had neoplasia, four dogs had
hypothyroidism and one had protein losing glomerulopathy. In
only one case was no risk factor identified. Follow-up periods
from the time of diagnosis of demodicosis were two to seven
years during which time only three dogs died or were
euthanased. Clinical, but not necessarily parasitological, remis-
sion was achieved in the remaining dogs with appropriate miti-
cidal therapy and management of the underlying cause.
However, all cases experienced intermittent periods of clinical
relapse and some dogs required continuous long-term miticidal
therapy.
Amitraz
In the UK, the only licensed product for the treatment of
canine demodicosis is amitraz applied topically at 0.05% solu-
tion once every five to seven days. We recommend total-body
clipping or, at least, clipping of the affected areas. The antimi-
crobial shampoo of choice is applied first and the dog towel-
dried prior to amitraz application.
Side effects associated with amitraz acting as an α2-adrenergic
agonist include hypotension, bradycardia, hypothermia and
mydriasis. Its use may also be associated with hyperglycaemia,
sedation for 24 to 72 hours, convulsions, ataxia, personality
change, diarrhoea, anorexia, vomiting and transient pruritus.
Care should be taken to ensure that amitraz therapy does not
exacerbate any underlying disease. Small dogs with generalised
skin disease are overrepresented in our cases and increased
systemic absorption of amitraz with the risk of side-effects is an
issue in treatment choice. In small dogs, we may use 0.025%
solutions or occasionally only 50% of the body surface is treated
at any one time. The use of a residual dip such as amitraz does
limit the use of topical antibacterial shampoos that may be
useful in controlling pyoderma.
Assessing the case for therapy
Orally-administered miticides
For many of the above reasons amitraz may not be the treat-
ment of choice in an individual dog. If the risk of side-effects or
exacerbation of underlying disease in unacceptable or if the
response to amitraz is poor or already causing adverse effects,
owners are commonly offered milbemycin or ivermectin alter-
natives.
Ivermectin – In the UK, this product is not licensed for use in
the dog. The injectable ivermectin formulation (10mg/mL)
used in cattle, sheep and pigs is the most commonly used
product. We use it in non-herding dog breeds orally at a dose
rate of 600 µg/kg daily. Prolonged treatment may be required in
adult-onset cases: 10 to 18 weeks being the average for parasiti-
cidal remission. Ivermectin is never given to Rough-Coated
Collies, Shelties, Old English Sheepdogs or any individual with
a merle- coloured coat or blue iris. If in doubt about the toxicity
in an individual dog, a test dose of 100 µg/kg subcutaneously is
given and the dog monitored for ataxia and mydriasis for 24
hours. The margin of safety for ivermectin in dogs is much
narrower than in other species and unexpected toxicity can
occur in any individual. One of our dogs, which had previously
tolerated a 10-week course of oral ivermectin, was inadvertently
given a single dose of 900 µg/kg for one day by her owner. The
dog developed typical but fortunately reversible signs of toxicity
within hours. Clinical signs of toxicity include ataxia, hyperme-
tria, disorientation, depression, mydriasis, tremors, ptyalism,
hyperaesthesia, blindness and coma.
Any therapeutic protocol in adult-onset demodicosis must
include management of the underlying disease. However,
although long-term clinical response compatible with good
quality of life is achieved in more than 80% of our cases,
repeated or continual therapy is required, as is the practical and
financial commitment from the owners.
Therapeutic options
The majority of dogs with adult-onset demodicosis treated at
our institution receive a combination of miticidal and anti-
microbial therapy. Our most frequently used systemic antimi-
crobial agent is cephalexin at a dose rate of 20 to 30 mg/kg
twice daily for a minimum of three to four weeks and for six to
eight weeks in cases of deep pyoderma and pododemodicosis.
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Clinical
Milbemycin oxime – A number of studies have reported the
References
1. Duclos DD, Jeffers JG, Shanley KJ. Prognosis for the treatment of adult-
onset demodicosis in dogs: 34 cases (1979-1990). J Am Vet Med Assoc 1994;
204:616-619.
use of milbemycin oxime in dogs with generalised demodicosis
in the USA, Australia and the UK.3,4 A study performed here
investigated the response of dogs with adult-onset demodicosis
to treatment with milbemycin oxime.5 Fifteen dogs, from 2 to
14 years old, were treated including three West Highland White
Terriers and four Shih Tzus. Pododemodicosis was a major or a
partial feature of the disease in seven dogs. None of the dogs
had unmanageable underlying disease. Milbemycin was admin-
istered for 120 days at a dose rate of 0.5 mg/kg daily and there-
after at 2 mg/kg for up to a further 120 days if required.
Adjunctive antimicrobial therapy was used as the case
demanded. Three dogs were parasitologically in remission after
treatment for 120 days but four dogs deteriorated during the
trial. The remaining eight (53%) dogs were clinically controlled
but were not cured.
2. McEwan NA. Demodectic mange in adult dogs. In: Proceedings of the British
Small Animal Veterinary Association Annual Congress, British Small Animal
Veterinary Association, 1991:167.
3. Mueller RS, Bettenay SV. Milbemycin oxime in the treatment of canine
demodicosis. Aust Vet Pract 1995;25:122-126.
4. Hertage MA, Skelly BJ, Reading MJ, Dunn KJ. The use of milbemycin oxime
in the treatment of generalised demodicosis and chronic sarcoptic mange. In:
Proceedings of the British Small Animal Veterinary Association Annual
Congress, Birmingham, British Small Animal Veterinary Association, 1995;222.
5. Foster AP, Shaw SE. Treatment of canine demodicosis with milbemycin
oxime. In: Proceedings of the Association of Veterinary Teachers and Research
Workers Annual Meeting, Scarborough. Association of Veterinary Teachers
and Research Workers, 1995:8:1C24.
Suggested reading
Lemarie SL. Canine demodicosis. Compend Contin Educ Pract Vet 1996;8:354-
368.
In our experience, milbemycin is a useful drug for
adult–onset demodicosis because of its minimal side effects,
good efficacy (including cases of pododemodicosis) and its
excellent owner compliance.
Paradis M. Ivermectin in small animal dermatology. Compend Contin Educ
Pract Vet 1996;20:193-200, 459-469.
(Accepted for publication 21 September 1999)
Generalised demodicosis in the dog: the unresponsive or
recurrent case
AK BURROWS
Murdoch University Veterinary Hospital, Division of Veterinary and Biomedical Science, Murdoch, Western Australia 6150
performed on every case of generalised demodicosis. A direct
impression smear of a pricked lesion should be assessed for the
presence of degenerate neutrophils, cocci and rod-shaped
bacteria. Samples containing rods should be submitted for
culture and susceptibility testing.
An antimicrobial drug with bactericidal activity that achieves
good concentration in the skin may be empirically selected for
the management of superficial bacterial pyoderma but the treat-
ment of deep bacterial pyoderma should be based on culture
and susceptibility testing of the contents of an intact bulla or
tissue biopsy. Antimicrobial therapy must be administered at
the appropriate dose rate for a minimum of four weeks for
superficial bacterial pyoderma and six to eight weeks for deep
bacterial pyoderma.
any cases of seemingly unresponsive or recurrent
generalised demodicosis in the dog are not truly resis-
tant at all. Instead, the apparent failure of therapy
M
results either because a treatment program has not been devised
or adhered to correctly or the animal has a concurrent under-
lying disease. The following discussion outlines five common
reasons for apparent failure of therapy in generalised demodi-
cosis in the dog.
1. Failure to identify and control concurrent super-
ficial and/or deep bacterial pyoderma
Concurrent bacterial pyoderma is present in most cases of
canine generalised demodicosis and will contribute to immuno-
suppression. The bacterial pyoderma may be superficial, with
papules and pustules, or deep, with furuncles, oedema,
cellulitis, severe pain and draining tracts that coalesce to form
large exudative erosions and ulcers with adherent crusts. Many
dogs with deep bacterial pyoderma are lethargic and febrile with
a generalised lymphadenopathy and septicaemia.
Topical antibacterial therapy with chlorhexidine or benzoyl
peroxide shampoo is an important adjunct to antimicrobial
therapy.
2. Failure to identify and manage a concurrent
medical problem.
Staphylococcus intermedius is the organism most often cultured
from dogs with pustular demodicosis. Gram-negative organisms
such as Pseudomonas aeruginosa and Proteus mirabilis are less
frequently isolated but are commonly resistant to routinely
prescribed antimicrobial drugs.
Several recent studies have highlighted the causal relationship
between adult-onset demodicosis and the presence of concur-
rent systemic disease. Adult-onset demodicosis is defined as
onset of disease after 12 months of age for small, medium or
large breed dogs and after 18 months of age for giant breed
dogs. Diseases causally associated with adult-onset demodicosis
Routine cytologic evaluation of the contents of an intact
pustule, bulla or exudate from a draining tract should be
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