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

Mange Mites

Advocate®: Effective Against Sarcoptic Mange

Sarcoptes scabiei is able to infect a wide range of mammals, with the various sub-species being relatively host-specific. The type found on dogs is Sarcoptes scabiei var. canis; this mite does not infect cats.

The Parasite

Sarcoptes scabiei is the mite originally been described by Gerlach in 1857 and found in humans. Sarcoptes scabiei is able to infest a wide range of mammals, while the various subspecies tend to be relatively host-specific.

Thus, one may find in the literature both Sarcoptes scabiei var. canis and Sarcoptes canis. Sarcoptes canis does not infect cats. However, cats can be parasitized by a similar-mange mite called Notoedes cati (Hering, 1836). Infection occurs by direct contact between hosts.

Female mites are 200 – 400 µm long, round to oval in shape and white in colour. The first two pairs of legs project anteriorly, bear long, unjointed stalks with suckers, and extend beyond the body. The two posterior pair of legs are rudimentary and do not extend beyond the border of the body. These legs lack suckers in females, possessing long bristles instead.

Fig. 1: Sarcoptes scabiei var. canis female

The nymphal stage is similar to the adult female stage of the mite. The off-host survival time of mites is rather limited and, as usual with permanent parasites, is dependent upon temperature and humidity. At room temperature, all Sarcoptes stages will survive for 2 – 6 days only; the maximum reported time has been 18 days under optimal conditions.

Life Cycle

The whole life cycle of the mite takes place in the keratinaceous layer of the host’s epidermis. Copulation takes place in burrows created by the mites, where the female lays up to three eggs per day over a period of 2-3 weeks.

The life cycle from the egg through one larval and two nymphal stages to the adult may be completed, under favourable conditions, in only 10 days. However, on average, the normal development time is 2 – 3 weeks. The larval stage hatches from the egg and feeds and moults to the nymphal stage within the burrows in the skin. However, both stages frequently wander about on the skin surface.

Fig.2: Life Cycle of Sarcoptes scabiei var. canis

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

Pathogenesis and Clinical Appearance

Fig. 3: Clinical lesions of Sarcoptes scabiei var canis infection in a dog

Female mites create burrows in the stratum corneum, stratum lucidum, and upper Malpighian layer of the skin. Mites prefer skin with less hair and, as a result, initial lesions tend to occur on body parts with less hair, such as the ear margin, abdomen, axillary and inguinal regions, the elbows and hocks.

The infection spreads from these areas over the body. However, the incubation period remains unknown. The first visible signs are small nodules and pustules, as well as increased scaling.

The first clinical sign in infected dogs is the onset of pruritus; subsequently, alopecia, thickening of the dermis and wrinkling of the skin occur. Due to the intense pruritus, extensive excoriation occurs and secondary bacterial infection are common. In contrast to these „classical signs” of sarcoptic mange infections, some dogs display incessant pruritus with only erythema or minor excoriations.

Histopathology reveals a high degree of inflammation in the epidermis, with hyper- or parakeratosis. The corium typically shows only minor chronic inflammation.

Zoonotic significance

Sarcoptes can readily transfer from canine to human skin if there is close contact. Although mites from dogs can survive and burrow in human skin, they seem unable to breed on the abnormal host. Repeated close contact with the infested dog is necessary to maintain human infestation.

Diagnosis

Diagnosis of sarcoptic mange infection is by deep skin scraping to find the parasite. Multiple scrapings are necessary on skin areas without excoriation. Deep scrapings are necessary and should be performed to a depth where some bleeding occurs.

Scrapings should be examined under the microscope, and are best treated with 10% potash before examination. The presence of a single mite is sufficient for diagnosis. However, mites are often absent, even with multiple skin scrapings.

A diagnostic clinical sign, although non-specific, is the pinnal-pedal reflex.

Efficacy of Advocate®

A study was performed in South Africa to compare the efficacy of Advocate with that of a positive control (selamectin, applied as a spot on) against severe natural infestations of Sarcoptes scabiei var. canis.1

Dogs were treated twice, on days 0 and 28, according to the labeled instructions for each product. Efficacy was based on the presence or absence of mites, as well as clinical signs and lesions, over a 64 day period.

The overall success of the treatment was defined as a dog that complied with all of the following criteria:

  • No live mites or eggs found
  • Complete reduction of papules and crusts
  • Marked reduction (> 80%) in the extent of alopecia

A clinical assessment of the presence and extent of papules, crusting, alopecia and hyperkeratosis was conducted at several times during the study. Advocate was highly effective in eliminating Sarcoptes scabiei var. canis, and resulted in an almost complete resolution of clinical signs within 50 to 64 days of the first application (Table 1).

Table 1: Overall treatment success of Advocate® spot-on against Sarcoptes scabiei var. canis*
  Group 1 (n=15) (selamectin)  Group 2 (n=14)
(imidacloprid / moxidectin)
Efficacy and treatment success  Day + 22 Day + 50 Day + 64 Day + 22 Day + 50 Day + 64
Efficacy (%) (Mite counts)  100 100 100 100 100 100
Overall treatment success (%)** 6.7 (1/15) 66.7(10/15) 66.7 (10/15) 7.1 (1/14) 92.9 (13/14) 100*** (14/14)

* On naturally infested dogs in comparison to selamectin
** Overall treatment success=mite counts and clinical signs
*** One dog in the Advocate-treated group showed some residual hyperkeratosis at day + 64 however the case was judged to be a treatment success

Questions about the product?

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References

  1. Bayer Study No. 25841

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