Psoroptic Mange

Synonyms

• Sheep Scab
• Psoroptic scabies
• Psoroptosis

Introduction

Psoropitc mange is the disease caused by the non-burrowing mite, Psoroptes ovis (common name Scab mite).

Description: The mite looks very similar in appearance to Chorioptes, being oval in shape with long legs, but is almost visible to the naked eye. It has pointed mouthparts and jointed pedicles which have suckers on the distal aspect.

Hosts: Sheep, Cattle, Goats, Horse, Rabbit, Camelid

Life cycle: Egg- Larvae- Nymph- Adult is confined to the skin surface. This life cycle takes around 10 days to complete. Adult female life expectancy is around one month and she lays 2-3 eggs per day, hence a mite population on an animal can expand rapidly.

This mite is found worldwide, but has been eradicated from Australia and New Zealand.

• Occurs in cattle, sheep, horses, goats, rabbits and other animals
• Host-specific
• Psoroptes cuniculi in ear canals of rabbits, horses, goats and sheep

Pathogenesis

• The ears are painful and intensely pruritic

• Affected rabbits shake their heads and scratch their ears

• The inner surfaces of the pinnae are covered with brown, scaly, fetid material, and the skin beneath is raw

• Mites are grossly visible

• Histologically, there is chronic erosive and proliferative eosinophilic dermatitis
  • The mites are non-burrowing and thus are found only in the exudate, not in the tissue

Diagnosis

• Microscopic examination for mites (low magnification)

• Appearance

Control

• Infestations are difficult to eliminate from a colony
  • Ivermectin is usually effective.

• P.equi at base of mane, tail and forelock in horses
• P.ovis in sheep (sheep scab)and cattle
  • Thickened skin and dry scales and crusts
  • Starts at withers and spreads due to self trauma
  • Microscopically:
    • Spongiotic, hyperplastic or exudative superficial perivascular dermatitis
    • Eosinophils

Pathogenesis

• Economically important ectoparasite of sheep

• Causes sheep scab
  • Wool loss, restlessness, biting, scratching of infested area and decreased productivity through decreased weight gain
  • Usually seen in late autumn and early winter (although may also occur in late summer)
  • Population numbers decline after shearing due to a change in the micro-climate, then build up again as the fleece grows
  • Notifiable in UK

• Mites found under scabs and in skin folds

• Lesions most common on flanks, neck, back and shoulders

• Causes pruritic condition of cattle

• Active in keratin layer

• Mouthparts abrade the skin

• Antigenic material in mite faeces can lead to hypersensitivity reactions

Diagnosis

• Skin scraping

• KOH added

• Warm slide over a bunsen flame

• Examine under a microscope

Treatment

• Sheep
  • Plunge dipping; no less than 1 minute and must dip head at lease once
  • Can treat with avermectins or milbemycins by injection

• Cattle, horses and rabbits
  • No licensed product for horses in the UK
  • Cattle and rabbits can be treated with avermectins, milbemycins or topical acaricides