Introduction

Active Forms

Resting Forms

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  :
  • 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  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

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 7 (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.