Demodicosis

Description

An inflammatory parasitic disease of dogs and cats caused by Demodex. Rarely also affects horses, cattle, sheep, goats and pigs. The mites live in hair follicles and infestation may lead to secondary bacterial infection and furunculosis.

Signalment

Commonly affects the dog and more rarely the cat. Breed predilections Age predilections Often animals less than 12 months of age although adult onset is recognised. Increased incidence in Siamese and Burmese cats.

Pathogenesis and epidemiology

• Squamous demodecosis
  • Less serious
  • Dry reaction
  • Alopecia, desquamation and skin thickening
  • Absent to mild pruritus

• Follicular/pustular demodecosis
  • More serious
  • Skin invasion by staphylococci
  • Skin becomes wrinkled, thickened and contains pustules which ooze serum, blood or pus
  • Affected animals may be seriously disfigured
  • Severe pruritus is associated with secondary infection

• Immune factors are important in determining the severity and occurrence of demodecosis
  • Familial susceptibility
  • Immunosuppression
  • Immunosuppressant therapy

Diagnosis

• Liquid paraffin applied to a skin fold

• Deep skin scraping

Control

• Not easily accessible to acaricides due to their deep location in the skin

• Repeat treatments needed

• Recovery may take several months

• To aid acaricide penetration, clipping a dog's coat and washing is recommended

From Pathology

• Demodex are normal inhabitants of hair follicles and sebaceous glands
• Have to have increased number of immature mites to classify as infestation
• Host-specific
• Occurs in dogs, cattle, sheep, goats, pigs, horses and cats
• Transmits during nursing from dam to offspring
• Demodex canis in dogs:
  • Generalised or localised
  • Mainly young dogs affected or adults with other disease (hyperadrenocorticism, hypothyroidism)
  • Often inherited in pure bred
  • Grossly:
    • Localised: scaly, erythematous, macular, alopecic areas; usually face or front legs
    • Generalised: large, coalescing lesions, patches, erythema, alopecia, scales, crusts
  • Microscopically:
    • Localised: lymphoplasmacytic perifolliculitis with hyperkeratinisation, sebaceous adenitis, low pigment, intraluminal mites
    • Generalised: perifolliculitis and follicular hyperkeratosis, follicular pluggingf, bacterial proliferation, bacterial neutrophilic folliculitis
      • May cause folliculat rupture -> furunculosis, cellulitis, lymphadenitis and septicaemia

Dogs

Cats

Cattle

Goats

Pigs

Sheep

Horses