The availability of a new blood test is driving hopes that sheep scab can be eradicated in the foreseeable future.

This was the key message delivered at a recent webinar hosted by the UK’s Sustainable Control of Parasites in Sheep (SCOPS) group.

The purpose of the event was to reflect the latest thinking on how best to deal with the disease, which is now thought to be endemic in the UK and Ireland.

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

Challenges to the control of sheep scab

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 Moredun Research Institute. Its efficacy has been confirmed on the back of trials carried out in England. This work is still ongoing.

Blood test

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

"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, flock owners 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.

"The antibodies can be picked up by the new test some two weeks before scabs physically appear," Burgess added.

“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.

"It is important that the animals actually tested are randomly sampled from within a flock," Burgess concluded.