Sheep Scab
Sheep scab, or psoroptic mange, is a form of allergic dermatitis caused by infestation of the skin surface with the scab mite Psoroptes ovis. It is considered to be the most contagious endemic ectoparasite diseases affecting sheep in the UK.
Key facts
Why is it important?
Sheep scab has been identified as one of the most important diseases for UK sheep farmers from both financial and welfare perspectives. It is one of the most contagious diseases affecting sheep and causes annual losses of £78 – 200m to the UK sheep industry.
Economic losses associated with reduced performance are due to loss of ewe condition, poor lamb growth, reduced quality of skins and wool damage. Untreated infestations can be fatal.
A brief history of sheep scab in the UK
What do the mites actually do?
As the mites feed on the surface of the skin they scrape it with their mouthparts and deposit faeces directly onto the skin resulting in an allergic-type reaction. The intense irritation causes the sheep to rub, kick, scratch and nibble the affected area resulting in raw skin and the formation on a scab at the site of the damage.
Transmission
Sheep scab mites are usually transmitted by direct contact between sheep. However, as the mites can survive for up to 19 days off the host they can also be transmitted via fence posts, trees, bushes, gates etc that infested sheep have been rubbing and scratching on.
Scab can also be introduced from neighbouring flocks as well as new and returning stock. Sheep trailers and other equipment can be potential sources of infection if not properly disinfected between farms/flocks.
Clinical Signs
Early Signs
Itching and scratching, rubbing on fences/gates etc, nibbling flanks, dirty discoloured fleece.
Developing Disease
Yellow/brown crusty lesions, skin exudate, damp/matted fleece
Advanced Disease
Large areas of wool loss, thickened and inflamed raw skin, dry crusty scabs, poor body condition and weight loss, secondary bacterial skin infections, potential death.
While scratching and rubbing may indicate sheep scab these signs are also seen with chewing lice which is common in UK sheep flocks. It is important to ensure accurate diagnosis through consultation with your vet.
It is also important to consider subclinical disease where the animals appear normal but are a source of infection for others. Animals which have been infested can develop immunity and appear heathy while carrying small numbers of mites in hidden areas (around the eyes, ears and crevices between the hind legs).
Using an inappropriate treatment or treating for the wrong ectoparasite will be ineffective, prolonging the welfare issues and may also select for resistance.
Diagnosis
Whenever an outbreak is suspected it is crucial that a definitive diagnosis is sought.
Traditional Diagnosis
Veterinary examination and skin scape to look for sheep scab mites. This method is heavily reliant on operator experience, and the accuracy of diagnosis can be low.
Moredun’s Sheep Scab Blood Test (ELISA)
This detects antibodies that are specific to sheep scab mites so this test can accurately determine if the clinical signs are due to sheep scab mites or another reason. The test can also detect mites before clinical signs are present. The test must be used at the flock/management group level and is not recommended for testing individual animals.
The Moredun ELISA test is available commercially as a diagnostic service through the Wales Veterinary Science Centre.
Prevention and Control
Notifiable in Scotland
In Scotland sheep scab is a notifiable disease. That means you must tell the Animal and Plant Agency (APHA) immediately if you suspect you have it in your flock. Failure to do so is an offence. In England, Wales and Scotland local authorities can force you to treat your sheep or take other action if the disease is present in your flock and you don’t take appropriate steps.
Biosecurity - Quarantine
Good biosecurity can prevent the introduction of sheep scab mites and other infectious diseases in a flock. - Quarantine: Separate newly acquired and returning sheep for at least two weeks before introducing to the main flock and observe for clinical signs of disease. Carry out the ELISA test and treat if necessary.
Biosecurity - Diagnosis & Treatment
It is crucial that all infested sheep are identified including subclinical cases. Quarantined sheep must not be introduced to the main flock until treatment is completed and shown to be successful.
Biosecurity - People, fencing & equipment
Anyone in contact with infested sheep (shearers, scanners, veterinarians etc) must disinfect their protective clothing and wash exposed skin with hot water before leaving the premises. All equipment in contact with sheep should be cleaned and disinfected after use. Good quality, well maintained fencing will help control the introduction of scab mites by preventing contact with neighbouring flocks. Ideally there should be at least two parallel lines of fencing preventing sheep-to-sheep contact.
Treatment - OP Dipping
Organophosphate: Plunge dipping with OP remains the most effective method for control of sheep ectoparasites (sheep scab mites, lice, ticks and keds). - Plunge Dipping is essential. spray races, jetters and pour-ons are ineffective for the treatment and prevention of scab. These methods are unable to effectively kill all the sheep scab mites. - Dipping should be carried out according to the manufacturer’s instructions and ideally by using a professional contractor
Treatment - ML Injectable
ML injectables offer some advantages over dipping such as increased safety for operators, ease of use, lower stress for animals, reduced need for specialist facilities and reduced environmental impact. - ML resistance is present across the UK - MLs are heavily relied on for control of worms so should not be used as a preventative for sheep scab – only when you have an active infestation
Downloads & links
Related Resources
Video
Stop the Spread - Moredun Animation
Link
Sheep Scab App
Visit siteLink
Sheep Scab Biobank
Visit siteDownload
Take control of sheep scab
DownloadDownload
A test is best
DownloadDownload
Invest in the test
DownloadDownload
Who let the tups out?
DownloadDownload
A race to the finish
DownloadKey resource
Factsheets
Stop the Spread: Taking Contol of Sheep Scab
Published 28/02/2023Who's involved
Our Experts
Frequently asked questions
FAQ
Sheep scab, or psoroptic mange, is caused by infestation of the skin surface with the scab mite, Psoroptes ovis.
The disease is characterised by crusty yellow scabs on the skin surface and is accompanied by restlessness, scratching, loss of wool, bleeding wounds and loss of condition.
Scab is common throughout the year, but majority of outbreaks occur between September and March.
Psoroptes mites can survive off-host for 16-19 days and sources of infestation include anything the infested sheep has contacted, e.g. fence posts, trees, equipment, trailers and anyone handling the sheep.
Accurate diagnosis is crucial to ensure that the correct treatment is given at the right time. For example, other skin infections or infestation by multiple ectoparasites can affect treatment selection.
Diagnosis is classically performed by a skin scrape but sensitivity can be low and often fails to detect sub-clinical disease. A diagnostic blood test (ELISA) for sheep scab, developed at Moredun, is available and can diagnose the disease before clinical signs appear.
Good biosecurity, such as well maintained double fencing, can prevent the introduction of sheep scab into a flock by preventing direct contact with neighbouring flocks.
Test all incoming stock to see if treatment is required, quarantine for at least two weeks and observe for signs of infestation such as nibbling, rubbing, scratching, deranged wool and areas of wool loss.
- The Lewis & Harris Animal Health and Welfare Project is a successful example of a living lab approach, co-developed with crofters, vets, regulators, and the local community to tackle endemic livestock diseases.
- Initially focused on controlling sheep scab, the project evolved through collaboration with Moredun and James Hutton scientists.
- Funded by the Scottish Government, it highlights how participatory design and community leadership can drive practical, policy-aligned changes in livestock health management.
- From the beginning, the project was rooted in local knowledge. Two experienced crofters were hired as coordinators and worked closely with the Lewis & Harris Sheep Producers Association (LHSPA) and the island’s sole veterinary practice.
- Crofter workshops held across Lewis & Harris gathered insights on disease risks, biosecurity practices, and barriers to adopting best practices, directly informing the project.
Relevant Reports
The first cartoon titled ‘a test is best’, describes exactly how the blood test works through identifying antibodies produced in response to a protein in the sheep scab mite faeces.
The second cartoon called ‘invest in the test’, describes the financial gain in testing sheep as opposed to treating an entire flock, giving a comparison of £160 for testing 12 individuals including vet fees as opposed to £1100 for treating a flock of 500 sheep.
The third design labelled ‘who let the tups out’, delivers a key biosecurity message about bringing animals on to the farm, which can be a particular issue when new tups are bought in.
It advised farmers to isolate new tups for at least two weeks, carry out the test and when the results are clear they can be turned out with the ewes.
The fourth cartoon, called ‘a race to the finish’, details the issue of store lambs coming in to be finished and the importance of testing for sheep scab, so if treatment is needed there is plenty of time for the withdrawal period to pass.
The final design ‘it is good to talk about scab’, looks at the need for coordinated treatments and the importance of talking with neighbours and sharing an effective biosecurity plan.
