8/9/2019 Canine Demodicosis and Its Management

1/3

CANINE DEMODICOSIS AND ITS MANAGEMENT

Canine demodicosis is a common disease encountered in small animal practice. It is a difficult

disease to cure and cases are often seen by referral dermatologist, either due to a failure to

diagnose the disease or because of difficulty in management. Localised demodicosis in young dogs is

very common and 90% of these will cure spontaneously. Generalised demodicosis can be divided

into juvenile onset (before the first year of age) and adult onset (after 2 years). A further subdivision

of generalised cases is demodectic pododermatitis. These may result as a failure of complete cure of

a generalised cases or present as foot lesions alone. Generalised cases in particular may be very

difficult to cure, especially the adult onset group. In these it will be necessary to identify an

underlying cause and treat it if success is to follow. In approximately half the cases it is not possible

to identify an underlying cause and in these continuous treatment is required with a guarded

outlook.

DEMODEX MITES

Three Demodexmites have been described in the dog. Demodex canis is the commonest.Demodex

injai is a slightly longer mite. Both mites are inhabitants of the hair follicle. A third mite inhabitants

the outer layers of the skin and is shorter than the other two. It is often called Demodex cornei due

to its location.

CLINICAL SIGNS

There are variable clinical signs. Localised alopecia in short haired young dogs is suggestive. The

generalised cases may show alopecia, pustules, comedones, and in early cases erythema which may

be mistaken for allergic disease. In chronic cases the colouration becomes blue grey. In time theentire body may be affected. In early stages it is the head and feet which are primarily affected.

DIAGNOSIS

Deep skin scrapings

Hair plucks

Tape strip preparations (for D. cornei)

Examination of pustule contents

Biopsy (mainly chronic demodectic pododermatitis)

8/9/2019 Canine Demodicosis and Its Management

2/3

TREATMENT OPTIONS

A. LICENSED PRODUCTS (UK)

Amitraz

This is the oldest licensed product. It is a monoamine oxidase inhibitor which affects the

neurological system of the mite. In the UK it is formulated as a 5% dip which is applied

weekly . In the United States the label is for half this strength applied every two weeks.

Using the UK system the success rate is approximately 90%. This depends on good

compliance. It is also advisable to clip long haired dogs before application of the product

Amitraz is also available as a spot-on in combination with metaflumizone. The advantage

with this treatment is that the veterinarian can apply the product thus eliminating

compliance problems. In the authors clinic it is applied every two weeks which is off label.

A series of cases of drug induced Pemphigus foliaceus apparently caused after application of

the product has been seen in the United States which has lead to the withdrawal of the

product recently. This has not been seen in Europe and for the moment there are no plans

to discontinue its use.

MoxidectinMoxidectin is available as a spot-on product in combination with Imidacloprid. It causes

paralysis and death of the mite. It is licensed for weekly use. Preliminary reports suggest that

it is not very effective in advanced cases.

B. UNLICENSED PRODUCTS

Ivermectin. The drug is given orally once a day at a dose of 0.6 mg/kg. Certain breeds show

side effects. These are Collies and other herding breeds. This is caused by an MDR1 gene

defect which renders such dogs unable to pump drugs which cross the blood brain barrier

out of the brain. The signs are vomiting, lethargy, inappetance, and ataxia. There is a blood

test available to detect this gene defect. Alternatively it is also possible to begin with a low

dose of 0.1 mg/kg and build up over a week or so to the full therapeutic dose if no side

effects occur. Ivermectin is effective in more than 90% of cases.

Milbemycin. This drug is given at a dose of 2mg/kg and is often used with Ivermectin

failures. Adverse effects are much rarer than is the case with Ivermectin and dogs which will

not tolerate this drug can usually be treated with Milbemycin. This treatment is expensive

Doramectin is similar to Ivermectin and there is a report of successful treatment with this

drug

Selamectin. Recently a report suggests that daily dosing orally with Selamectin is effective.

TREATMENT OF RESISTANT CASES

Griffin recommends combination therapy in cases which have failed to respond to one or both

agents mentioned above. He combines Ivermectin 450-600 mcg/kg twice weekly orally with amitraz

every two weeks either as spot on or dip.

8/9/2019 Canine Demodicosis and Its Management

3/3

REASONS FOR TREATMENT FAILURE

Owner induced(poor compliance) This includes improper use of the medication, not applying

the spot on to the skin, infrequent application of the product, premature discontinuation of

the product, not shaving the dog if the dip is used

Veterinarian induced. This includes no or late diagnosis due to failure to skin scrape of

failure to perform adequate deep scrapings, failure to treat secondary infection with long

term antibiotics, and stopping the treatment too soon. In addition some of the dogs wil l be

pruritic due to secondary infection. The use of glucocorticoids in these cases is

contraindicated as it favours the multiplication of mites and worsening of the secondary

pyoderma.

A concurrent disease which has not been diagnosed, for example hypothyroidism

hyperadrenocorticism, internal parasites.

FURTHER READING

Griffin treatment of Canine Generalised demodicosis British Veterinary Study Group November 2011

29-35 November 2011

Mueller R.S Treatment protocols for demodicosis: an evidence based review. Veterinary

Dermatology 15. 75-89 2004