Demodex spp

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Demodex canis under light microscopy
Demodex injai viewed under light microscopy[1]
Demodex gatoi viewed under light microscopy[2]
Secondary bacterial skin infection due to Demodex canis[3]

Demodex spp are a parasitic mite of the skin of dogs worldwide.

TEST Demodex mites are considered to be a normal part of the cutaneous microfauna in the dog and are transmitted from the bitch to the pups during the first days of life[4].

Species which are pathogenic to dogs include:

  • Demodex canis[5]
  • Demodex gatoi
  • Demodex cati
  • Demodex injai[6][7]

The parasite normally resides within the hair follicles of dogs and secondary bacterial infections do occur. The role of Staphylocoocus pseudintermedius as a secondary contaminant is an important consideration[8]. No evidence of Wolbachia spp endosymbionts has been detected with this parasite as is seen with Dirofilaria spp[9].

Clinically affected dogs with localized demodicosis present with alopecia, dermatitis, comedones, follicular papules and pustules, scaling, and crusting[10]. Pruritus is uncommon unless bacterial infection is involved.

Ocular lesions may occur, such as blepharitis and conjunctivitis.

In immunocompromised patients, generalized demodicosis occurs due to premature apoptosis of peripheral leucocytes. This is thought to be the mechanism underlying the immunosuppression observed with generalized demodicosis[11][12].

Generalised demodicosis is characterized by variable pruritus, alopecia, crusting, and secondary pyoderma, often affecting the entire body. A secondary ceruminous otitis externa is common.

Diagnosis is made by deep skin scrapings, although mite numbers are often small. Skin cultures are essential, because dermatophytosis such as Microsporum spp and yeast such as Malassezia spp[13] often occur concomitantly with this disease[14].

Differential diagnoses would include ringworm, pemphigus foliaceous, bacterial folliculitis, Notoedres spp and Otodectes spp.

Chlorhexidine and benzoyl peroxide shampoo weekly washes are indicated as antibiotic guidelines recommend to limit the use of broad spectrum antiobiotics in favor of topical antiseptics.

Miticidal drugs are usually indicated, such as:

  • Ivermectin at 600 μg/kg every 24 hours orally for 6 - 8 weeks or until negative skin scrapings is achieved.
  • Milbemycin orally at 1 - 2 mg/kg daily[15]
  • Moxidectin at 0.3 mg/kg after daily gradual dose increases from 0.05mg/kg
  • Doramectin orally or subcutaneously at 0.6 mg/kg

It is recommend to extend the treatment to beyond negative scrapings. The prognosis is good for most dogs, and better in juvenile than adult dogs, as juvenile dogs generally don’t have underlying diseases[16].

Prognosis of generalized demodicosis in older dogs is unpredictable because of its potential relationship with systemic disease. Some cases spontaneously resolve.

References

  1. Capc Vet
  2. Capc Vet
  3. Treaschig Veterinary Clinic
  4. Greve JH & Gaafar SM (1966) Natural transmission of Demodex canis in dogs. J Am Vet Med Ass 148:1043–1045
  5. Owen IL (2005) Parasitic zoonoses in Papua New Guinea. J Helminthol 79(1):1-14
  6. Milosevic MA et al (2013) PCR amplification and DNA sequencing of Demodex injai from otic secretions of a dog. Vet Dermatol 24(2):286
  7. Ordeix L et al (2009) Demodex injai infestation and dorsal greasy skin and hair in eight wirehaired fox terrier dogs. Vet Dermatol 20(4):267-272
  8. Kuznetsova E et al (2012) Influence of systemic antibiotics on the treatment of dogs with generalized demodicosis. Vet Parasitol 188(1-2):148-155
  9. Borgo SN et al (2009) PCR analysis for Wolbachia in human and canine Demodex mites. Arch Dermatol Res 301(10):747-752
  10. Mueller RS et al (2012) An update on the therapy of canine demodicosis. Compend Contin Educ Vet 34(4):E1-E4
  11. Singh SK et al (2011) The role of apoptosis in immunosuppression of dogs with demodicosis. Vet Immunol Immunopathol 144(3-4):487-492
  12. It V et al (2010) Association of canine juvenile generalized demodicosis with the dog leukocyte antigen system. Tissue Antigens 76(1):67-70
  13. Tarallo VD et al (2009) Efficacy of Amitraz plus Metaflumizone for the treatment of canine demodicosis associated with Malassezia pachydermatis. Parasit Vectors 2(1):13
  14. Shipstone M (2000) Generalised demodecosis in dogs, clinical perspective. Aust Vet J 78:240–242
  15. Mueller RS (2011) Evidence-based treatment of canine demodicosis. Tierarztl Prax Ausg K Kleintiere Heimtiere 39(6):419-424
  16. Mueller, R et al (2011) Treatment of demodicosis in dogs: 2011 clinical practice guidelines