CANINE DEMODICOSIS IS
A COMMON SKIN DISEASE
in which there is an increased
number of Demodex mites, normal
inhabitants of canine skin. Three
mites have been identi ed, with
their usual site in brackets: Demodex
canis (hair follicle and sebaceous
gland), Demodex injai (hair follicle and sebaceous gland) and Demodex
cornei (stratum
corneum).
Development
of the disease is
associated with
immune deficiency
(Paterson, 2008). Demodex canis is
the most commonly seen mite and
is described in this article. Demodex
cornei is less common although
clinically indistinguishable (Miller,
Grif n and Campbell, 2013).
Demodex injai has a different
clinical presentation, mainly a greasy
seborrhoea that tends to be dorsal,
with a breed predisposition for
terriers, especially the West Highland
white and Shih-Tzu. This form is
not described further in this article
and interested readers are referred
to other texts (Miller, Grif n and
Campbell, 2013; Paterson, 2008).
Clinical presentations
Demodicosis occurs in various
clinical manifestations. These are
localised, generalised (further divided into juvenile onset and adult onset)
and pododemodicosis, which may be
seen in both localised and generalised
forms.
Authors vary in their definitions
of what constitutes localised and
generalised, and also concerning the
age of onset. Paterson (2008) defines
localised demodicosis as having fewer than five patches
on the skin,
and one foot
only involved in localised
pododemodicosis.
Generalised
demodicosis is defined as more than five patches of affected skin and two or more feet in
the pododemodicosis form. Juvenile
onset disease is de ned as occurring
between three and 18 months of age
and adult onset after three years. There
is no uniformly accepted standard for
the above definitions but this author
prefers those described by Paterson.
Adult onset generalised
canine demodicosis
Signs
- Age of onset is after three years and
frequently older than this - Care needs to be taken with dogs
presenting at around the three-year
age group, as it is not unusual for
the disease to remain undetected
for several years if careful sampling has not been done. A
detailed history will be
essential in these cases. - Regardless of the age of onset
the generalised
forms are clinically
indistinguishable. Early
signs are erythema,
alopecia, scaling,
comedones, crusts and haemorrhagic
lesions. Generalised
erythema accounts for
the old description of the disease “red
mange”. This colour
is highly suggestive of
demodicosis but may be
misdiagnosed as atopy. - With chronicity,
secondary infection with Staphylococcus pseudintermedius
is common. Occasionally Proteus
and Pseudomonas can be involved.
Bacterial infection in untreated cases
is frequently severe with cellulitis,
furunculosis and generalised
lymphadenopathy. In chronic skin
cases the skin is often a blue-grey
colour and should suggest the disease
and prompt skin scrapings. - Lesions tend to be most severe
in the predilections sites – the facial
area, neck and feet, but ultimately may
involve the entire body. - Depression, lethargy and anorexia
develop in advanced neglected cases
and fatality is possible.
Underlying causes
- In all cases of generalised
demodicosis the immune system is
depressed. - In adult onset cases, an immune
suppressing disease occurring later
in life is responsible for the sudden
appearance of demodicosis. - These cases are much rarer than the
juvenile onset cases. - Possible underlying causes
include hyperadrenocorticism (both
naturally occurring and iatrogenic),
hypothyroidism, diabetes mellitus,
neoplasia, leishmaniasis, and
immunosuppressive treatments for
neoplastic or immune-mediated
diseases. - Underlying trigger diseases may
become apparent some time after
cutaneous lesions are apparent, thus
these dogs should never be considered
cured and frequent monitoring is
advisable.
Diagnosis
- History and physical examination.
- Identification of mites from hair
plucks, acetate tape impression smears,
deep skin scrapings, and in chronic cases,
where the skin is
lichenified particularly
in interdigital areas, and
biopsy. - Complete blood
count, biochemistry,
endocrine function
tests, radiography
and ultrasonography
depending on clues
from the history and
physical examination.
Treatment
- Successful treatment
in adult onset cases is more difficult than in the juvenile
onset cases. - Treatment of underlying causative
diseases is essential and if successful
will result in success rates comparable
with juvenile onset cases. - In those cases where the
underlying disease has not been
diagnosed or has not yet manifested
itself, some improvement and
control may be possible but relapse
will quickly occur on cessation of
treatment. As many as 50% of cases
may fall into the category.
Licensed treatments
- Amitraz (Aludex, MSD). This is
applied as a 0.05% solution (50ml in five litres) of water weekly. The dip
is left on the coat and not rinsed off.
Clipping long-haired dogs will aid
penetration. Treatment is continued
until two weeks after clinical cure and
negative skin scrapings. Sedation is
common particularly after the first
application and tends to diminish as a problem subsequently. When
secondary infection is confirmed cytologically, anti-bacterial treatment is
essential. The product should not be
used on Chihuahuas. - Moxidectin/Imidacloprid
(Advocate, Bayer). This treatment is in
the form of a spot-on applied weekly,
and is continued for two weeks
beyond clinical cure and negative skin
scrapings.
Success rates with both these
treatments vary according to the
literature. In the author’s experience
and with good compliance the success
rate in first opinion cases is in excess
of 90% in juvenile onset cases and a similar percentage in adult onset
cases where the underlying cause is
determined and successfully treated.
If this is not possible such cases need
maintenance therapy and frequent
monitoring.
Unlicensed treatments
Most of the unlicensed treatments
that have been used are avermectins.
Two are mentioned here:
- Ivermectin. This drug is the most
widely used at a dose of 0.2-0.6mg/
kg by mouth daily. It is often started at
0.1mg/kg and gradually built up over
a few weeks to monitor for possible
neurological side-effects. These are
particularly common in Collie dogs
and their crosses but can occur in
other breeds. - Milbemycin. This is given at a
dose of 0.5-2mg/kg by mouth daily.
Neurological side-effects may occur
but are less common compared to
ivermectin. With both these drugs
the success rate is equivalent to the
licensed treatments. - Recent attention has focused on a
product licensed for fleas and ticks in
the UK. - Fluralaner (Bravecto, MSD). This
product is a chewable tablet given
once every three months. Fourie and
others (2015) reported on a study
involving 16 dogs that were treated
for generalised demodicosis either
with uralaner or imidacloprid/
moxidectin spot on. Both treatments
resulted in clinical cure but uralaner eliminated mites at 56 and 84 days,
whereas mites were still present
at these times with imidacloprid/
moxidectin. However, the product
was administered monthly in this study. Weekly administration
according to the more recent license
has been shown to give better results. - A larger open study in
Poland (Karas-Teczay and
Dawidowicz, 2015) treated 163
dogs with uralaner for generalised
demodicosis. The overall response
to therapy was 100% with 87.1%
skin scrape negative after one month
and the remainder after two months; 37.4% of these dogs were over two
years of age when the disease was
diagnosed, which suggests that it
may be effective in dogs with true
adult onset disease. This definition of
adult onset disease differs from that
of Paterson described in this article.
Further studies are under way to see
if these promising results can be
replicated.
References and
further reading
- Fourie, J. and others. (2015) Ef cacy
of oral administered uralaner
(Bravecto) or topically applied imidacloprid/moxidectin (Advocate) against generalised demodicosis in
dogs. Parasites and Vectors 8: 187. - Karas-Teczay, J. and Dawidowicz,
J. (2015) Ef cacy of uralaner for the
treatment of demodicosis. In: Proceedings
of the Annual Congress of the
European Society and College of
Veterinary Dermatology, pp124-125.
Miller, Grif n and Campbell (2013)
In: Muller and Kirk’s Small Animal
Dermatology, 7th edition, p305.
Elsevier. - Paterson, S. (2008) In: Manual of Skin
Diseases of the Dog and Cat, 2nd edition,
pp104-109. Blackwell.
