Optimism grows that sheepscab can be eradicatedthroughout the UK

Sheep scab is a condition that causes terrible suffering for those animals afflicted by it, writes Richard Halleron.

By The Newsroom
Sunday, 27th March 2022, 9:41 am

Fifty years ago, the goal of totally eradicating the problem seemed to be in sight. But this proved to be false dawn.

Sheep scab, caused by the mite Psoroptes ovis leads to major economic losses to the UK flock and impacts sheep welfare. Attempts to control the disease through legislation began in the late 1800s, with compulsory treatment enforced from 1928. By 1992, complete eradication had failed and disease control was deregulated. There had been compulsory notification of 100 cases on UK farms that year.

Estimated UK case numbers by 2004 were at 7000, with Wales having the highest prevalence. A 2010 study identified 36% of Welsh sheep farms had a sheep scab outbreak in the previous five years. All studies show areas of persistent infection and sheep on common grazing are twice as likely to be infected as others.

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In England and Wales, it remains a legal requirement to treat infected animals and all others in the flock. Local authorities have the power to enforce treatment, prevent movement and control scab on the commons.

In 2010, Scotland again made the disease notifiable. The Sheep Scab (Scotland) Order 2010 places a legal obligation on any person who has reason to believe that sheep in their possession or care have sheep scab to notify their local Animal & Plant Health Agency (APHA) office as soon as possible. In 2019, Wales announced £5 million funding for a Sheep Scab Eradication Project with details yet to be released.

Sheep scab is spread by any contact with live mites. This is usually through direct sheep-to-sheep contact on commons, via break-ins, at markets or in livestock lorries. Adult mites can survive for up to 17 days in the environment enabling indirect spread via rubbing posts, trees, hedges and fences. Shearing combs and cutters, contaminated clothing, tags of wool or scabs can also harbour and spread mites. In rare cases, scab can infect cattle.

So much for the background: the good news is that the availability of a new blood test is driving hopes that sheep scab can be eradicated in the UK.

This was the key message delivered courtesy of a recent National Sheep Association (NSA) hosted webinar, reflecting the latest thinking on how best to deal with the disease, which is now thought to be endemic in the UK.

The cost of the disease to the UK economy ranges from £80m - £200m per annum with 10% - 15% of sheep farmers experiencing scab in any one year.

There are also a number of challenges to control, where scab is concerned. These include an over reliance on just two classes of drugs: the macrocyclic lactone (ML) injectables and organo phosphate (OP) plunge dips.

Significantly, there are no new control chemistries in the pipeline. ML resistance was reported back in 2018 and this phenomenon is now gathering pace across the UK. As a consequence, this method of scab treatment has to be handled very carefully.

The new blood test was developed by scientists at Edinburgh’s Morden Research Institute. Its efficacy has been confirmed on the back of trials carried out in England. This work is still ongoing.

Stewart Burgesss, from the Moredun Institute, addressed the webinar. He explained that the new test will detect the presence of the disease some weeks prior to physical signs appearing.

Burgess added:“We recommend that the test is used as part of a whole flock or group control programme. At least 12 sheep must be tested in order to obtain an accurate scab assessment.

“The test is an important tool in dealing with scab and determining how we think about scab.

“We can now get on top of the disease before it gets a chance to spread. In other words, flockowners can intervene before it gets worse in the case of individual outbreaks.”

The new test detects antibodies against a protein from the sheep scab mite.

Burgess continued: “The antibodies can be picked up by the new test some two weeks before scabs physically appear.

“However, the antibodies remain in the blood for up to six months after a successful treatment. So we have to take this into account in assessing the results of the test.

“The test confirms if the animal has been exposed to the mite: it isn’t able to determine between an actively infested sheep and an animal that has been recently treated.”

The accurate interpretation of the new test results is critical. Mite antibodies will start to fall back after successful treatment of scab. So the test provides a snap shot of an animal’s antibody status at the time of the blood sample being taken.

But only by knowing the past disease and treatment history of the sheep is it possible to determine whether or not the antibody levels are pointing to a fresh infection.

Burgess concluded:“It is important that the animals actually tested are randomly sampled from within a flock.”

Bringing clusters of farmers together in hot spot areas is delivering a coordinated response to sheep scab result in the UK.

An ongoing trial, developed under the aegis of the Rural Development Programme of England (RDPE), got underway just under a year ago.

The campaign has been entitled: ‘For Flock’s Sake Let’s Stop Scab Together’.

Its objective is to demonstrate the effectiveness of a community-led approach to improve the control of sheep scab in three hotspot areas of England.

Within each hotspot, there are a number of ‘clusters’ of farms that share common boundaries or use the same common grazing, where the aim is to foster cooperation in the control of scab. Running over two years, the project offers up to 300 participating farmers a unique combination of on-farm advice, best practice training, and free blood testing.

The unique test at the very heart of the project was recently developed by scientists at the Moredun Research Institute.

The RDPE-funded project also covers the costs of visits by participating farmers’ local veterinary surgeon and two sets of blood tests. Also included is a face-to-face advisory visit by the vet for each farm to discuss scab control and biosecurity.

The scab hot spot areas identified were in the North West, the Midlands and the South West of England.

The recent NSA sheep scab webinar provided those involved with the three sets of farm clusters to report on the impact made by the project since its launch.

All confirmed the willingness of most farmers to take part. In some areas the project has been over-subscribed many times over.

There was also unanimous agreement that the new blood test works well under commercial farming conditions. In many cases, scab had been identified on units where the farmers in question had firmly believed they did not have a problem in the first place.

In terms of scab control, the project is pointing to the benefits of effectively dipping sheep and the need for farmers to work together with a common purpose.

The Sustainable Control of Parasites in Sheep (SCOPS) group chairman, Kevin Harrison, took part in the general debate afforded by the webinar.

He confirmed that the new testing and control pilot project is working in England, adding: “The sheep industry has shown that it is willing to invest its own resources in tackling the problem of sheep scab.

“But we need more funding and support from government to get us further down the road.”

Harrison foresaw the introduction of relevant legislation by government as being a critical step in the future development of an effective scab eradication campaign.

So how is sheep scab impacting on Northern Ireland’s sheep industry?

Postgraduate research veterinarian Paul Crawford is currently developing a farm management programme to address the challenge of sheep scab in Northern Ireland.

He spoke on this matter at the recent NSA webinar.

According to Crawford, very little has been done up to this point to quantify the impact of scab on Northern Ireland’s industry.

He went on to confirm that getting accurate data in this regard is his first priority, adding:“Eradicating sheep scab is now a confirmed objective for all stakeholder organisations operating within the sheep industry. And a working group was specifically set up to move the project forward.

“This took place in 2019. However, the intervening Covid-19 pandemic has greatly held up all work to this end.”

Crawford admitted that sheep scab is, almost certainly, endemic within Northern Ireland’s sheep flocks.

He continued:“As part of the work undertaken up to this point, we have explored some of the barriers to better control.

“People with particular expertise in specific areas were asked to input their thoughts to the working group on how best to get to grips with scab.

“Working group members have also met representatives of the Agriculture, Environment and Rural Affairs committee at Stormont, to brief them on the need to eradicate sheep scab.”

Crawford also confirmed that no academic research had been carried out, up to this point, to investigate the real prevalence of scab in Northern Ireland.

As part of his ongoing PhD research project he has recently carried out an internet survey of sheep farmers on the matter.

“Initial indications are that scab is more prevalent than the official figures published by the Department of Agriculture, Environment and Rural Affairs would indicate,” Crawford further explained

He believes that bespoke legislation will be required to eradicate scab, drawing parallels with the ongoing BVD eradication programme.

Crawford commented:“The current BVD initiative is getting us 93% of the way, or thereabouts, towards the full eradication of the disease.

“But there remains a core of farmers who are not complying fully with the current measures.”

He added:“Legislation is the only way that these matters can be addressed. And there are obvious parallels, in this regard, between BDV and scab eradication.”

Northern Ireland’s sheep scab working group has applied for Biotechnology and Biological Sciences Research Council (BBSRC) funding to allow it to more fully investigate the impact of the disease, across a range of disciplines: economic, animal welfare and environmental.