Sheep scab is a disease caused by the non-burrowing mite, Psoroptes ovis. It is highly contagious between animals and can rapidly progress to severe disease once sheep are infected.
Sheep scab is a form of allergic dermatitis, which is caused by the faeces of the Sheep scab mite.

 

 

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Life Cycle

 

Psoroptes ovis mites live at the base of the fleece and feed on dead skin cells and skin discharge. The mite spends the majority of its life cycle on one host. Eggs are laid by female mites that can lay up to 80 eggs in their lifetime of about a month, which hatch into larvae after three days. The larvae then hatch into nymphs, mature to adult mites and the cycle begins again. The whole life cycle takes between 11-19 days.
Due to the disease being highly contagious, along with the number of eggs that the mite can lay, it only takes one female mite to cause an entire flock infestation.1
 

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Reference:

1. Lewis, C. (1997) Update on sheep scab. In Practice, November/December, 1997, 558-564. http://inpractice.bmj.com/content/19/10/558.short 

 

Signs of Sheep Scab

 

The signs of sheep scab include severe itching and self-trauma due to an allergic reaction to the mites, their saliva and faeces, rubbing on gates and the ground, biting their flanks, pawing at their shoulders and stamping. This results in loss, damage or staining of wool, reduced weight gain or weight loss in on-going cases due to irritation causing decreased feed intake. Secondary blowfly strike may be noticed as the skin damage creates an ideal breeding ground for blowfly to lay eggs. They then hatch into larvae which bury into the skin causing extensive skin damage.1 Significant loss of condition, secondary infections, hypothermia and eventually death can result.

Sheep scab is not the only cause of itch in sheep so a correct veterinary diagnosis is important before commencing treatment.

 

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Reference:

1. The Centre for Food Security and Public Health http://www.cfsph.iastate.edu/Factsheets/pdfs/psoroptes_ovis.pdf

 

How do sheep become infected?

 

The most common route of spread is directly from sheep to sheep, which occurs when animals are tightly packed together such as during transport or at sales. Shared grazing can also lead to neighbouring flocks passing on the infection. Farm personnel can carry mites on their boots or clothing and similarly, sheep can also pick up mites from contact with contaminated objects, such as by rubbing on fence posts or from vehicles that have transported infected sheep. Bought-in sheep or loan rams entering the farm can introduce scab into a previously unaffected flock.

 

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How to diagnose Sheep scab?


Skin scrapings must be taken by a vet and examined under the microscope to confirm the presence of Psoroptes ovis mites. Scrapings taken from the edge of the damaged area using a scalpel scraped at right angles over the skin surface which will demonstrate large numbers of mites.

 

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Prevention and control of sheep scab

 

Control of sheep scab is crucial and prevention should be based around

  • Correct use of anti-parasiticides
  • Biosecurity measures (coordinated regionally).

 

The timing of treatment and a collaborative approach is essential and should take into account a number of factors:

  1. Preventive treatment with an appropriate anti-parasiticide, used at the correct time and in accordance with the treatment guidelines.
    1. All in contact animals and any new animals coming onto the farm, such as bought in stock or loan rams, should all receive appropriate preventative treatment, as well as resident flocks in which mites have been diagnosed. 
  2. Biosecurity measures to keep mites out and prevent re-infestation after treatment.
    1. Incoming stock should be treated and quarantined for at least three weeks and the same goes for decontamination before restocking. This accounts for the life cycle of the mites and the fact that they can survive off the host for up to 17 days.
    2. If bought-in stock is certified as having already been treated, a producer needs to find out what treatment was used and exactly when it was carried out.
    3. Maintaining secure fencing is paramount to prevent transfer of mites between neighbouring flocks and double fencing can be helpful in achieving this.
    4. Any potentially contaminated environment, object or shared equipment must be disinfected and debris, such as wool on fences, removed.

 

    

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Reference:

  1. NADIS Bulletin. Control of Sheep Scab http://www.nadis.org.uk/bulletins/control-of-sheep-scab.aspx

 

 

 

Treatment options

 

  • Plunge dip
  • Injection with a macrocyclic lactone anti-parasiticide chemical e.g. doramectin (DectomaxTM)

 

 

 

For more information see: www.nadis.org.uk/bulletins/control-of-sheep-scab.aspx
Or www.scops.org.uk/ectoparasites-sheep-scab.html

 

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