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), which affects sheep.

Other species of Psoroptes mite affect a variety of species including Cattle, Goats, Horse, Rabbit, Camelid, however, all mites are host specific and will be discussed later.

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.

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. The mite can survive off the host and so transmission via housing and bedding is possible. Most transmission occurs from direct contact such as at markets or in livestock transporters.

Predilection site: Lesions are most common on flanks, neck, back and shoulders

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

Pathogenesis

The mite is active in the keratin layer of the skin and has abrasive mouthparts. It feeds on exudate of lymph, skin cells and bacteria caused by a hypersensitivity reaction to antigenic mite faeces, by the host. This causes intense pruritus, leading to self trauma, crust and scale formation and inflammation.

The disease is most prevalent in autumn and winter months, however does still occur in the summer, especially in sheep that have not been shorn.

Psoroptic mange in sheep is a notifiable disease in the UK

Clinical signs

• Severe pruritus
• Evidence of self-trauma (loss, damage or staining of wool)
• Inflammation with exudate followed by a yellow crust
• Weight loss or reduced weight gain in young stock
• Secondary bacterial infection or Blowfly strike

Diagnosis

• History and clinical signs
• Skin scraping to microscopically identify mites (low magnification). Mites are found under scabs and in skin folds

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

•  

• Causes pruritic condition of cattle

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