ISSN 2398-2942      

Sarcoptes scabiei

icanis

Synonym(s): Sarcoptes scabiei var. canis, S. scabiei


Introduction

Active Forms

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Resting Forms

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Clinical Effects

Epidemiology

Habitat

  • Epidermis of the dog and fox and will survive a few days to 2 weeks on man.
  • Female in burrow in epidermis as far as spinous cell layer.
  • Male on surface of skin and enters burrows.
  • Eggs in burrows.
  • Larvae/nymphs in pockets off burrow, or larva tunnels to surface and enters at new skin fold or hair follicle to form pockets.

Lifecycle

  • See lifecycle diagram Lifecycle Sarcoptes scabiei - diagram :
    • 1. Egg.2. Larva.3. Nymphs (3).4. Adult male and female.

Transmission

  • Transmission by direct contact when probably larvae or newly fertilized females are transferred.
  • Very contagious with rapid transmission between in-contact dogs; transmission occurs from foxes to dogs, clinical signs after 6-11 days.
  • Direct physical contact required; a lot of anecdotal evidence that infection is transmitted when dog rolls where fox has rolled. Foxes often harbor large numbers of mites.
  • Mites can survive a day or two off host (low temperatures and 100% humidity required; 10-15° female mites survive for 4-21 days, room temperature all stages survive 2-6 days). Little evidence of transfer via the environment, even those that are heavily infected.

Pathological effects

  • Antigens are assumed to be mite bodies, feces and hatching and moulting fluids.
  • Immune hypersensitivity reactions, both immediate type I and delayed type IV, seem to be involved.
  • Infiltrating cells are primarily mononuclear cells (T lymphocytes, macrophages and B lymphocytes).
  • IgE and mast cells and eosinophils may be found in the vicinity of the mites, burrows and papules.
  • Disease is due to the immunopathological response of the dog Skin: sarcoptic mange.

Pathogenesis

  • Following infection, female mites begin to burrow into the skin, produce eggs and mite numbers build up.
  • Initially there is no immune reaction to the parasites, the period of sensitization, for 3-5 weeks.
  • Mite numbers continue to increase, but now the animal is sensitized and the interaction between the hypersensitivity reaction and antigen produces the clinical signs and pathology.
  • Mite numbers may now decrease, removed physically by scratching, and developing stages are probably killed or inhibited by a protective immune response.
  • Some animals may clear the infection but, in others, large or small numbers of mites will persist producing chronic antigen exposure and chronic disease.

Clinical

  • Lesions particularly on ear pinnae, around eyes, muzzle, elbows and hocks, and spread on to head, abdomen, groin Scabies alopecia Skin: sarcoptic mange.
  • Itchy papules may be seen initially.
  • Focal or generalized hyperkeratosis with crusting of the skin, alopecia, severe pruritus and itching, and self-trauma and thickening of the skin.
  • The animal can become debilitated with secondary infection and lymphadenopathy.

Histopathology

  • Changes are variable Skin: sarcoptic mange.
  • In outer layers, simply the burrow, mites and feces.
  • Cytolysis in living epidermis and dermo-epidermis junction with increasing parakeratosis around the necrotic burrow.
  • Perivascular and dermal infiltration of mononuclear cells, eosinophils, etc.
  • Some vasculitis and spongiotic lesions beneath the burrows.

Other Host Effects

  • Some skin is eaten.
  • Female mite begins burrow in skin crease and enters by chewing with its chelicerae and moving its mouthparts from side to side. A flap forms and is lifted and the burrow is enlarged in this way with the claws on the legs. Female burrows down as far as spinous cell layer - 0.5-5 mm a day.
  • Growth of epidermis lifts the burrows, eggs, etc and the keratinized epidermis of the earlier part of the burrow is rubbed off.

Control

Control via animal

  • Acaricide treatment of the dog.
  • A second or third treatment at intervals of 1 week may be needed (a number of people use 1 treatment of phosmet and repeat after 14 days).

Control via chemotherapies

  • Phosmet.
  • Amitraz Amitraz.
  • Oral ivermectin Ivermectin (0.3 mg/kg PO every 7 days for 4 treatments) - very effective but toxic to breeds such as collie.
  • Oral milbemycin Milbemycin oxime (2.0 mg/kg PO every 7 days for 6 treatments).
  • Topical selamectin (Revolution).
  • Topical lime sulfur.

Control via environment

  • None required.
  • It may be useful to vacate kennel and bedding for a few days and wash the bedding in acaricide.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Bornstein S, Thebo P & Zakrisson G (1996) Evaluation of an enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of canine sarcoptic mange. Vet Derm (1), 21-28 VetMedResource.
  • Burgess I (1994) Sarcoptes scabiei and scabies. Advances in Parasitology 33, 235-292 PubMed.
  • Mellanby K (1944) The development of symptoms, parasitic infection and immunity in human scabies. Parasitology 35 (4), 197-206 Cambridge University Press.

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