Psoroptic Mange

Also Known as: 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 causesintense pruritus, leading to self trauma, crust and scale formation and inflammation.

It is not only economically important to the sheep industry due to poor fleece quality and weight loss, but it can also pre-dispose to life-threatening condition such as Blowfly strike, as the blowflies find the damaged skin ideal for egg laying.

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 'used to be a notifiable 'disease in the UK, but has been de-regulated since 1992

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

Treatment/ Control

Infestations are difficult to eliminate from a flock so a key factor in control is to not allow it to enter.

• New stock should be isolated for at least three weeks before mixing with the main flock
• Plunge dipping is curative and preventative
  - dip must contain the Organophosphate diazinon or the Synthetic Pyrethroid cis-cypermethrin
  - plunge dipping must last for at least one minute and the head should be fully submerged twice during this time
  - the sheep must be kept moving when in the dip as the movement displaces air from in the fleece allowing better penetration
• Can treat with avermectins or milbemycins by injection
  - only moxidectin has any prophylactic effect
  - need two injections 7 days apart or one single dose (doramectin only) 
  

Other species

Cattle

Uncommon in the UK.

Affects withers mainly

Can be treated with avermectin, milbemycins or topical acaracides

 

Horse

Notifiable in the UK, but has not been recorded for many years

No licensed product for treatment of horses in the UK

 

Rabbits

'Ear canker mite' in rabbits

Externam auditory canal infection is often asymptomatic, but may cause scratching and head shaking behaviour

Can be treated with avermectin, milbemycins or topical acaracides

 

 

References

Aitken, I.D, (2007) Diseases of Sheep fourth edition, Blackwell Publishing

Fox, M and Jacobs, D. (2007) Parasitology Study Guide Part 1: Ectoparasites, Royal Veterinary College

Hindson, J.C, (2002) Manual of Sheep Diseases second edition, Blackwell Publishing

Taylor, M.A, Coop, R.L, Wall, R.L, (2007) Veterinary Parasitology third edition, Blackwell Publishing