Felis ISSN 2398-2950

Sarcoptes scabiei

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

Contributor(s): Karen Campbell, Susan Dawson, Maggie Fisher, David Scarff

Introduction

Classification

Taxonomy

  • Family: Sarcoptidae.
  • Genus: Sarcoptes.

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Clinical Effects

Epidemiology

Habitat

  • Epidermis of the cat and will survive a few days to 2 weeks on man - no evidence of ability to complete life cycle in human skin.
  • Female 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 also S. scabiei life cycle Lifecycle: Sarcoptes scabiei - diagram .
    1. Egg Sarcoptes scabiei: egg . 2. Larva. 3. Nymphs (3). 4. Adult male Sarcoptes scabiei: male and female Sarcoptes scabiei: female .

Transmission

  • Transmission by direct contact when probably larvae or newly fertilized females are transferred.
  • Very contagious with rapid transmission between in-contact animals; transmission occurs from foxes to dogs to cats, clinical signs after 6-11 days.
  • Direct physical contact required; a lot of anecdotal evidence that infection is transmitted when dog/cat 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°C 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 cat 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

  • See also sarcoptic mange Sarcoptic mange.
  • Lesions particularly on ear pinnae, around eyes, mouth, elbows and hocks, and spread on to head, abdomen, groin.
  • 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

  • See also sarcoptic mange Sarcoptic mange.
  • Changes are variable.
  • 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 cat.
  • A second or third treatment at intervals of 1 week may be needed.

Control via chemotherapies

No treatment for Sarcoptes licensed for use in cats.
  • Frontline (fipronil) Fipronil - licensed for use in puppies. No evidence of efficacy in cats.
  • Oral ivermectin Ivermectin(0.3 mg/kg PO every 7 days for 4 treatments).
  • Oral milbemycin Milbemycin oxime(2.0 mg/kg PO every 7 days for 6 treatments).
  • Topical selamectin.
  • Topical lime sulfur.
    Amitraz Amitraz occasionally causes very severe reactions in cats Amitraz toxicity.

Control via environment

  • None required.
  • It may be useful to wash the bedding in acaricide.

Diagnosis

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Further Reading

Publications

Referred papers

  • Brunetti B, Vitiello A & Delfino S (1998) Findings in vivo of sarcoptes scabiei with incident light microscopy. Eur J Dermatol 8(4), 266-267 (Epiluminescence microscopy trialled for identification of Sarcoptes scabiei in human patients).
  • Bornstein S, Thebo P & Zakrisson G (1996) Evaluation of an enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of canine sarcoptic mange. Vet Dermatol 7, 21-28 (ELISA test for dogs).
  • Burgess I (1994) Sarcoptes scabiei and scabies. Advances in Parasitology 33, 273-292 (Review covering primarily human infection but relevant to any species).
  • Mellanby, K (1994) The development of symptoms, parasitic infection and immunity in human scabies. Parasitology 35, 197-206 (Was and remains the classical description of the development of infection and disease in any host).

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