Thought to be the first sheep disease in Britain to incur statutory controls, scab is a highly contagious skin condition which causes significant animal welfare concerns. Once thought to be eradicated from the UK, scab is now considered endemic again (present throughout the national flock) and is responsible for major financial losses in the UK sheep industry as well as at individual farm level. Limited treatment options are available, and developing resistance gives real concerns over future control. 

So where does scab come from, how can it be spotted, and what should be done to treat and prevent it?  

History of sheep scab in Britain 

Awareness of the history of this disease is important in understanding the current situation and future control measures.  

1869 – Scab first made notifiable in Britain 

Early 1900’s – compulsory dipping begins 

1928 – By law, the Sheep Scab Order requires notification, movement controls, isolation and treatment. Treatment was by dipping with various chemicals no longer permitted due to toxicity and safety issues 

1948 – organochlorine chemicals approved for use, aided the eradication campaign 

1952 – Eradication believed to have been achieved in Britain, with ongoing surveillance of imported animals 

1973 – Scab reappeared in British sheep flocks and spread rapidly. Previous control measures re-introduced including dipping. 

Early 1980’s – OP dips became available but despite supervised compulsory dipping, scab case incidence increased. Injectable ML (macrocyclic lactone) products are shown to be effective against scab mites, but dipping is still compulsory. 

Check your pets symptoms
Symptom Checker

1992 – Scab deregulated (although some control measures remained) due to the high cost and ultimate failure of eradication efforts. The lack of compulsory dipping led many to rely instead on the more practical injectable products. 

1997 – Sheep Scab Order controls movement of affected sheep 

2001 – first reports of ML resistant worms 

2010 – Sheep Scab (Scotland) Order 2010 makes the disease notifiable again in Scotland 

2017 – ML resistant scab mites identified.  

  • Blood test for sheep scab developed at Moredun 

What is sheep scab? 

Sheep scab is caused by the mite Psoroptes ovis, a tenacious little fella who can survive off sheep for up to 19 days. This ability to survive in the environment, on fence posts, trailers, hedges and equipment (e.g. shearing combs), makes it a challenging opponent to tackle. 

On the sheep, scab mites are surface dwellers but cause an intense allergic dermatitis (inflammatory skin reaction). This results in itchy sheep who are restless, foot stamping, head shaking and biting at their own skin. Affected sheep will scratch on any available surface, resulting in wool loss and transferring mites to infect the next passing animal!  

Thick yellow scabs form on the skin and can become infected or bleed. The intense discomfort distracts sheep from feeding and uses extra energy in the process, so affected sheep may lose condition rapidly. Severely affected individuals may seizure (have fits) and can die due to lack of nutrition or from secondary disease, with surviving animals requiring substantial supplementary feeding to restore body condition. 

In breeding sheep, scab infestations may result in poor pregnancy rates, low lamb birthweights, and reduced lamb viability, whilst fattening animals may struggle to reach finishing weights, and carcasses may even be condemned at slaughter. 

What to do if you suspect sheep scab 

Contact your vet who will arrange to visit your flock and take samples.  

Scotland: At the time of writing, sheep scab is notifiable, meaning it is the legal obligation of anyone owning or caring for sheep that may have scab, to notify their local APHA office as soon as possible.  

England and Wales: scab is not currently notifiable, but the Sheep Scab Order 1997 prevents the movement of scab affected sheep, unless for treatment, slaughter, to clear common grazing or under a license following inspection. 

Diagnosing scab 

Symptoms of sheep scab can be similar to that of lice and other skin diseases, and more than one process may occur at the same time. It is therefore vital to make an accurate diagnosis before treating affected animals appropriately. Inappropriate treatments; 

  • Delay effective cure  
  • Prolong suffering 
  • Waste time and money 
  • Increase risk of mites (and roundworms) becoming resistant  
  • Increase risk of scab spreading to other groups and neighbouring livestock 

Two tests exist to diagnose scab: 

Skin scrapes carried out by your vet

  • Simple and accurate – scab mites are easy to differentiate from other parasites. 
  • Quick – samples can be examined under the microscope at the veterinary clinic, so same day results are possible.   
  • Useful to identify other parasites such as lice 
  • Highly effective in cases showing clear symptoms of skin disease. 

The disadvantage of skin scrapes is that the absence of mites in a sample leaves a question: Are they not present or were they just not found? 

This is particularly important in recently purchased sheep or those returning from grazing away from home, where recent infection may not yet cause clear symptoms and low numbers of mites may not allow for detection by skin scrapes. Even low numbers of mites are enough to cause a scab outbreak in your entire flock however, so in these circumstances, blood testing can be invaluable.  

The blood test

  • Very sensitive – groups of up to 2000 sheep may be screened for scab by testing just 12 individuals. 
  •  Highly specific – false positives are unlikely to occur even when other parasites are present.  
  • Able to identify scab in sub-clinical cases where symptoms are not yet visible. 
  • Results will take a little longer than skin scrapings. 

It can take up to 2 weeks from first mite exposure, before blood tests will become positive, so the test is best used in cases where: 

  • No mites are visible on skin scrapes but there is still a high index of suspicion that scab may be present.  
  • Incoming or returning animals have been isolated for 2 weeks following arrival, then blood tested before joining the rest of the flock.  

Treatment  

Current options for treatment of scab affected sheep are already very limited and will be further diminished as resistance to these products continues to develop.  

Organophosphate (OP) plunge dipping 

  • Highly effective against scab, killing mites within 24 hours 
  • Residual effect lasting several weeks, reducing reinfestation from the environment.  
  • Also effective against ticks, lice and other parasites.  
  • Safe use and disposal of OP’s is vital for human and animal health as well as the environment. A certificate of competence from an approved training course is therefore required to purchase and use OP dips. Appropriate equipment is required including a suitable dip tank, but mobile dipping services now enable most farms to access this 
  • Dipping may not be suitable for heavily pregnant ewes, although hydraulic cage dippers reduce handling and stress so may be more appropriate 
  • Lambs cannot be dipped if under 15kg or with unhealed navels (i.e. under 8 weeks of age) 

Injection with macrocyclic lactone (ML) products  

Treatment using injectable ML products is a practical option for treating; 

  • Small numbers of sheep 
  • Sheep with open wounds or sores that should not be dipped 
  • Heavily pregnant or very recently lambed ewes 
  • Unfortunately, when ML’s are used to treat scab, roundworms are also exposed to the same product. This increases the risk of ML resistance forming in roundworms  (documented since 2001) as well as in scab mites (documented since 2018). 

The loss of efficacy of these products will leave only one option for treatment of sheep scab – OP dipping.  

Resistance 

To reduce resistance pressure; 

  • Test first to confirm the need to treat  
  • Use the most appropriate treatment for the stock and time of year e.g. injectable ML’s for heavily pregnant sheep or young lambs, but dipping may be more beneficial after shearing in summer and autumn when flies, ticks and lice are also of concern. 
  • When using injectables, follow the SCOPS code of best practice to ensure all sheep are treated accurately and correctly, at an appropriate dose for the heaviest animal in the group. 
  • Consider blood testing 12 ewes before lambing time, as treating pregnant ewes will be more practical and effective than trying to treat ewes and lambs during lambing! 

If you think a treatment has failed, DO NOT just retreat as this may make the situation worse. Speak to your vet who will guide you through the appropriate steps to take. 

Prevention 

Strict biosecurity protocols including quarantining and testing (2 weeks later) any purchased or returning animals, are key in preventing sheep scab entering your flock. In Scotland, where scab is notifiable, some sheep are being sold as dipped prior to sale, and some markets are offering a post-sale dipping service, so that purchased animals can be treated immediately before being transported to their new holding. This is especially useful to reduce the use of injectable ML’s where small numbers of animals are involved. 

In Shetland, a specific set of regulations exist meaning that all sheep imported to the islands are examined by vets on arrival at the pier and then transported to a community run facility where they can be dipped for scab. This coordinated biosecurity approach enables sheep producers in Shetland to protect their flocks from scab in a more effective way but relies on geographical control of incoming livestock which is not so achievable in mainland Britain.  

Well maintained boundary fencing is necessary to prevent (as far as is ever possible!) straying sheep, and where scab is confirmed, communication with neighbouring sheep keepers is key to coordinating treatments and avoiding reinfestations. Where boundaries cannot be enforced between farms or when common grazing is used, a coordinated approach to treatment is required, and this has been the subject of a recent pilot project on Scotland’s largest island. 

The Lewis and Harris Sheep Producers Association Project 

In the Outer Hebrides, the crofting communities of Lewis and Harris have been working alongside the island’s vets and specialists from Moredun to assess the control of sheep scab through large scale testing and strategic treatment.  

In February 2023, blood testing of 1260 sheep (12 animals per flock) was carried out in 1 week, followed by treatment of positive flocks with injectable ML’s. As the sheep were close to lambing, plunge dipping was not appropriate, however an ambitious plan was hatched and in Autumn 2023, around 28,500 sheep were gathered and treated using a mobile OP dipping contractor.  

In 2024, small scab outbreaks were reported on holdings or in groups that had not participated in the initial treatments. These were controlled effectively using injectable ML’s before a second round of dipping was carried out in the autumn, this time dipping over 30,000 sheep (over 90% of the island’s breeding sheep population).  

In early 2025, blood testing indicated that overall scab prevalence had reduced and a coordinated plunge dipping was carried out again in the autumn, with the island’s sheep producer’s association looking to find economically sustainable ways to continue this approach to scab control, beyond the conclusion of the project.  

The future 

Work is ongoing at Moredun to explore whether vaccination could reduce the severity of symptoms and therefore economic and welfare implications of infection with scab mites.  

In the meantime, it is imperative that we protect the treatment options that we currently have by following best practice use of injectable ML’s as well as strategic, coordinated, and safe use of OP dips when possible. There remains some reluctance amongst shepherds to talk about scab, and to contact neighbours when outbreaks occur, however communication in this instance can significantly reduce the impact of an outbreak and reduce the risk of reinfestation. 

If you would like to read more about sheep scab, the Moredun website has a wealth of information, and the experiences of the Lewis and Harris Sheep Producers Association project gives a fascinating insight into what can be achieved, as well as the indirect benefits to the community of coordinated control programmes.  

Further Reading 

Taking control of sheep scab – Moredun 

History of sheep scab eradication in the UK 

NADIS – sheep scab 

The Lewis and Harris Sheep Producers Association project in association with Moredun