Testing for sheep scab could prevent unnecessary treatment costs

Sheep scab is an intensely itching skin disease that costs the UK sheep industry between £78-202 million a year, according to research published in Vet Record. It’s caused by the parasitic mite Psoroptes ovis that infects around 9% of flocks annually, with rates significantly higher in some hotspot areas, University of Bristol research has shown.

For practicality reasons, many farmers administer treatment for sheep scab on a ‘just in case’ basis. However, using medicines simply as insurance is not only an ineffective control strategy, but is also expensive and leads to unwanted resistance issues, according to independent sheep consultant Lesley Stubbings.

Since the symptoms of sheep scab can take weeks to appear, testing is imperative to early detection. The sheep scab blood ELISA test can detect antibodies produced against the disease as quickly as two weeks after exposure.

Farmers are advised to quarantine new flock for 3-4 weeks upon arrival and test 12 animals from each group after the first two weeks. The cost of the ELISA blood test is around £84 for 12 sheep.

Testing will indicate whether the group of sheep has been infected with scab and whether treatment is necessary, Ms Stubbings explained.

“You cannot tell simply by looking at sheep if they are carrying scab mites. Clinical sheep scab can take weeks, if not months, to present itself, by which time much of the flock can be infected.

“The sheep scab ELISA test means scab can’t hide from us anymore. It makes it much easier for farmers to use the right product at the right time, knocking sheep scab on the head,” she added.

If the disease is detected on the premises, farmers have two options for treating the affected animals. They can either use an injectable group 3-ML such as Cydectin 2% LA that also prevents reinfestation for 60 days from a single dose. Or, they can choose to treat via plunge dipping using an organophosphate (OP) dip.

Ms Stubbings said it doesn’t matter which method farmers choose as long as every animal is treated correctly. Using an injectable is a practical option when there is only a small number of affected sheep or the farm doesn’t have facilities for dipping.

“The main thing when treating for scab is that you do it properly, whether using an injectable or a dip. There’s no reason why you shouldn’t use an injectable, providing it is used properly, meaning the correct dose is administered and all the animals are treated.”

Sheep scab is a disease of major economic and welfare implications, which is why correct control is so important, Zoetis vet Ally Ward explained.

“Scab is so itchy for sheep, and in the later stages, they will spend all their time rubbing, scratching and biting their wool to alleviate the itching. This is a real welfare concern,” she stressed.

In collaboration with Zoetis, manufacturer of Cydectin 2% LA, the Sustainable Control of Parasites in Sheep (SCOPS) produced a code of practice for using injectables, which can be found here: https://www.scops.org.uk/workspace/pdfs/best-practice-use-of-injectable-scab-treatments.pdf