Canine demodicosis

 Manoj karki (BVSC&AH)
Date: 2020/5/19

Canine demodicosis is a severe parasitic skin disease of a dog caused by overpopulation of the follicular mite of various demodex species. One of the most common cutaneous infection encountered in canine practice is demodicosis.

Demodex mites are normal flora localized in the skin of most apparently healthy dog, when Secondary bacterial infection of the hair follicle often occurs, and rupture of the hair follicle wall may lead to presence of free mites in the dermis and a severe pyogenic infection. Although, demodex canis is acquired by puppies within the first few hours of suckling it is a normal inhabitant of canine skin and demodicosis is not a contagious disease.

Fig: 1. Life cycle of Demodex canis: (1) the life cycle of Demodex includes, apart from the adult mite, egg, larva, and two nymphal stages; (2) the lifecycle happens in hair follicles. The puppy is infected by the dam during the first days of its life. The infestation is preceded by the multiplication of the mites on the dam’s skin (3). The mechanism, which accelerates the multiplication just before whelping, is not known. Most dogs harbor single, latent Demodex mites in their hairfollicles, living in quiet seclusion. In some individuals and in some circumstances the mites can start to multiply uncontrollably, leading into the symptomatic demodicosis.

Etiology:

Demodex canis is the main causative agent of canine demodicosis. The mites residue in the hair follicle and sometimes the sebaceous gland. Four stage are seen, the diamond shaped egg, the 6 legged larvae and 8 legged nymph form which develops into adult.

Generally three types of Demodex mites are found in dog. Demodex canis (long bodied mites), Demodex injai (large bodied mites) and Demodex cornei (short bodied mites)

Fig: 2. Demodex injai (10×magnification)

Fig: 3. Demodex canis and Demodex cornei (blue box)
at 10× magnification.

Pathogenesis:

The mites enter the hair follicle, reach the root and multiply. Due to inflammation the papilla is destroyed and the hair is lost. The parasite then enter the sebaceous gland where condition appear to be very congenial for the growth of mites, since the altered sebum is a very favourable medium for them to grow. The sebaceous gland may be dilated and become cystic and lined by squamous epithelium. Thus the skin comes to be covered by scaly material which may be desquamated. The sebaceous cyst may rupture, the spilled sebum causing inflammation locally. The blood vessels are congested and dilated.

Clinical sign:

The most common clinical sign are alopecia, scaly-crustly thickened skin with   hyperpigmentation, leechinification, erythema, pruritus and seropurulent discharge seems mostly on per ocular area, face, neck, shoulder and fore quarter region. Anemia may also occur in this condition due to loss of skin proteins and leukocytosis. Most case of demodecosis are non-pruritus unless there is secondary pyoderma. Very rare ulceration may develop, especially on the face and mucocutaneous area which may mimic autoimmune disease.

Canine demodectic mange is classified as two forms.

Localized and Generalized form

Localized form: The localized form typically starts as one or more focal alopecic lesion, erythema and comedomes in dog less than 1.5 years old. Usually only the head (perioral, peri ocular) or the forelimb are involved.  There is no significant pruritus. This is commonly seen in pups of 3 to 9 month old and spontaneous recovery without treatment.

Generalized form: Generalize demodicosis is a severe disease requiring aggressive therapy. This form involves the large part of the dogs skin and bears a guarded prognosis. Generalized form is however, characterized by number of area of localized disease or even infection in entire skin areas. Generalized demodicosis can be severe often complicated with secondary bacterial infection and life threatening.

It should be remember that every case of generalized demodicosis was localized form.

Juvenile onset demodicosis (onset prior to puberty) and adult onset demodicosis

Juvenile onset is by far the most common and although a serious disease, often a better prognosis than does adult onset. Adult onset is usually associated with severe internal disease and Is often very difficult to control.

Fig:3. Dog with lesions at face and neck regions

Fig: 4. Alopecia and scale/crusts formation throughout the body due to infestion of demodectic mite

Diagnosis:

Canine demodicosis is usually diagnosis by identifying mites in skin scrapping and hair plugs.

Performing of skin scrapping:

1. Some 3-5 site are selected for skin scrapping

2. The hair, if present, is clipped

3. The skin is gently squeezed between thumb and forefinger to force the mites more superficially in the hair follicle.

4.The skin is moistened with liquid paraffin or mineral oil

5. Some is also placed on the slide

6. The skin is then scraped using a blunted scalpel blade until capillary bleeding is observed.

7. The material is transferred to the slide

8. The entire slide is scanned using 10X objective

9. Focus on suspicious area using the 40Xobjective if necessary.

10. The proportion of live and dead mites of adult and young forms and of eggs should be recorded.

or

The scraping was placed in the test tube and 10% KOH solution was added. Then, the solution was gently heated (near up to the boiling) with frequent shaking for about 5-10 min until all the debris was digested. Often the solution was allowed to cool for some time and was allowed to centrifuge at 2000 rpm for 10min, supernatant were discarded and remaining sediment were a coverslip. The sediment was observed for mites with the help of compound (10x) microscope.

Prognosis:

 The prognosis for juvenile onset localized demodicosis is very good. The prognosis for juvenile for onset generalized demodicosis is always guarded.

The demodicosis mange upto 1 year of age were more susceptible to infection and the highest prevalence of the disease was found in winter season rather than summer or rainy season. Demodicosis is highly prevalent in dog whose immune system is distributed or not well developed. So it is highly recommended that dog should be given proper nourishment, immunization, deworming and care to avoid skin disorder like demodicosis.

Treatment and prevention:

Treatment should be occur in localized and generalized demodicosis

In localized, this is usually a self-limiting disease that cures spontaneously. Treatment with parasiticides is usually not warranted. But 10 % of case of localized demodicosis go on to become generalized. Therefore whether or not treatment is given a careful follow up is necessary.

In generalized demodicosis, it can be one of the most frustrating skin disease, one will ever treat.

Specific treatment of demodectic mange are:

Amitraz: 0.025% whole body dip applied every 2 weeks interval 5-8 application or till skin scraping are negative. Not recommended for cat and puppy

Ivermectin: 0.3-0.6 mg/kg bwt PO single dose

Moxidectin: 0.4mg/kg bw POsingle dose

Before application of medicine crust, scale and debris should be removed with soap and shampoo.

A course of antibiotic should be given to inhibit bacterial infection. Antibiotic therapy should be continued until the mite population is well controlled.

Reference:

1.    Ashfaq, K., et al. (2019).  “Alternative therapeutic approach to treat canine demodicosis”. EC veterinary science 4.4 :251-256

2.    Islam, M.M., et al. (2000). “Prevalence and pathology of demodectic mange in stray dog in Bangladesh”. Journal of science and technology. 11: 118-121

3.    Shrestha, D., et al. (2015). “Prevalence of demodectic mange in canine of KTM valley having skin disorder and its associated risk factor”. Int. Appl sci biotechnol, vol 3(3): 459-463

4.   Salem, N.Y., et al. (2020). “Canine demodicosis hematological and biochemical alteration”. Veterinary world.org., vol(13):68-72

5.   Bhatia, B.B., et al.(2016). “ text book of veterinary parasitology”. 4^th edition.

6.    Picture are taken from google.