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.

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.

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 and evidence of self-trauma (loss, damage or staining of wool) are the main signs to notice from within the herd. Once a closer inspection is made, inflammation and an exudate will be noticed on the skin and areas of yellow crust will also be present. In on-going cases,weight loss in adults, or reduced weight gain in growing animals, will be seen due to the irritation causing them to have a reduced feed intake. In some cases, secondary blowfly strike may by the first sign noticed, when the sore traumatised skin has become a perfect breeding ground for the blowfly.

Diagnosis

History and clinical signs are often enough to make presumptive diagnosis. Skin scraping to microscopically identify mites (low magnification) should be performed. 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

The dip must contain the Organophosphate, diazinon or the Synthetic Pyrethroid, cis-cypermethrin. The sheep must be dipped 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 the fleece allowing better penetration

Psoroptes can be treated with avermectins or milbemycins by injection, but only moxidectin has any prophylactic effect. Two injections 7 days apart or one single dose (doramectin only) are needed. 

Other species

Cattle

Psoroptic mange is uncommon in cattle in the UK. When present, it affects mainly the withers and can be treated with avermectin, milbemycins or topical acaracides.

Horses

Equine Psoroptic mange is notifiable in the UK, but has not been recorded for many years. There are no licensed products for treatment of horses in the UK.

Rabbits

Rabbits become infected by Psoroptes cuniculi causing 'Ear canker'. The external auditory canal infection is often asymptomatic, but may cause scratching and head shaking behaviour. It can be treated with avermectin, milbemycins or topical acaracides. For more information see the rabbit section.

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

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