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Demodicosis Brochure

You'll find a brochure about Demodicosis in the download area.

Animations

Gripping life cycle animations of this parasite you'll find in the download area.

Demodex Mites

Advocate®: Effective Against Demodicosis

Demodex is part of the physiological fauna of the skin in many, if not all, mammalian species, including the dog and man. Demodex canis is responsible for one of the most important skin diseases of dogs: canine demodicosis.

The Parasite

Fig. 1: Adult Demodex canis

Demodex canis (Leydig, 1858), the hair-follicle mite, is a white, oblong mite. Adult female mites measure 300 µm and the males about 250 µm (Fig.1).

It normally lives as a commensal in the skin of most animals, spending its entire life cycle in the hair follicles and sebaceous glands. Mites can be found in healthy dogs, albeit in small numbers. For Demodex canis, so-called ‘short-bodied’ and ‘long-bodied’ mites have been described, although whether these are individual species, subspecies or races currently remains undetermined.

The capitulum is horseshoe-like with clearly visible mandibles. The cuticula of the body resembles transverse wrinkles. Four pairs of stump-like legs end with 2 claw-like structures. The mites feed on cells, sebum and epidermal debris.

Life Cycle

Demodex mites are transmitted from the bitch to the nursing puppies within the first days after birth. Mites spend their entire life on the skin of dogs, where they reside in the hair follicles and, rarely, the sebaceous glands.

Four stages have been described for Demodex canis (Fig.2).

The developmental cycle starts with the larvae hatching from the fusiform eggs. The six-legged larvae moult to become the eight-legged first nymphal stage. This is followed by a second nymphal stage, which in turn moults to give rise to the final adult stage. The whole life cycle is completed in about 3 weeks. All stages of the mite can be found in the hair follicles, as well as the lymphatic system, bloodstream, and other bodily organs. Mites in these „extra-cutaneous“ locations are dead and have relocated to these areas by means of lymph or blood drainage.

Fig.2: Life Cycle of Demodex canis

To watch or download the animation of this life cycle please visit our download area.

Pathogenesis and Clinical Appearance

While Demodex canis may be present in the normal canine dermis, transmission occurs from the nursing bitch to the puppies within the first 3 days of life. Mites have been demonstrated in pups as young as 16 hours old. In contrast, puppies born by caesarean section and kept apart from an infected bitch do not harbor mites – a clear sign that no intrauterine transmission occurs.

Two forms of the condition are recognized: a localized and a generalized form. The generalized type may be further subdivided into juvenile-onset and adult-onset demodicosis.

Factors that adversely affect the immune system are important in determining the occurrence and severity of demodicosis.

Generalized demodicosis involves several areas of the body and these may be quite large in size. A dog with five or more localized lesions, involvement of an entire body region, or involvement of two or more feet is considered as having generalized demodicosis.

Generalized demodicosis may occur at a young age and if it does not resolve spontaneously with the maturation of the immune system, it will require treatment.

The pathological mechanisms involved in juvenile-onset demodicosis remain unclear.

Adult onset demodicosis could affect any age and is most likely to be triggered by factors such as an underlying deficiency of the immune system, diseases such as infection or neoplasia, and certain therapies, especially immunosuppressive agents.

In addition to the demodicosis, secondary pyoderma is common and can result in a pustular form of the condition, which is severely pruritic.

Zoonotic significance

Human infection is rare, thus the mite has a low zoonotic potential.

Diagnosis

The standard method for diagnosis of infection with Demodex mites is microscopic examination of deep skin scrapings and detection of mites.

To perform a skin scraping, the skin should be squeezed, thus expelling the mites from the depths of the hair follicles to the surface. Demodex mites are present in the skin of healthy dogs and a single mite found in a scraping may be consistent with a diagnosis of healthy skin. However, while it is not common to detect mites in healthy dogs, such a finding should not be ignored. Skin scrapings from several areas are necessary to confirm infestation.

Special care should be taken when the face and paws are affected to avoid causing excessive bleeding. Another option is to examine plucked hair for the presence of mites.

Efficacy of Advocate®

Eighteen dogs with severe generalized demodicosis were treated with Advocate to assess its efficacy against Demodex canis.1 Prior to inclusion, infection was determined by mite counts from deep scrapings. A minimum of two and a maximum of four treatments were applied; treatment days were 0, +28, +56 and +84.

On day 0 all dogs were treated. The number of subsequent treatments per dog depended on the presence or absence of Demodex spp. mites as determined during assessments one day prior to the second, third and fourth treatments.

If mites were found the animal was given another treatment; if mites were absent the animal was also given another treatment, unless it had been negative at the previous assessment.

In this study, two to four treatments with Advocate, applied at four-week intervals, were effective against Demodex spp. infestations in dogs. The reduction in the geometric mean numbers of mites at the end of the study compared to the pre-treatment numbers was 97.84% (Table 1).

Clinical symptoms of demodicosis, namely the occurrence of erythema, casts, scales, crusts and alopecia, improved accordingly, body weight increased and the overall condition of the animals improved markedly.

As indicated above, demodicosis is a multifactorial disease, and wherever possible, one should also identify and treat any underlying disease appropriately.

Table 1: Efficacy of Advocate® against Demodex canis
  Number of animals  Number of animals with mites  Geometric mean number of mites  Median number of mites  % Efficacy 
Pre-treatment  18 18  1756.20 2238  N / A 
End of Study  18  14  37.92  23.5  97.84 

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References

  1. Bayer Study No. 29819

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