A new blood test is giving hope that sheep scab can be eradicated in the UK and Ireland. But it is by no means a ‘silver bullet’.
Developed by staff at Scotland’s Moredun Research Institute, the new test acts to identify infected sheep before physical symptoms become apparent.
But according to Yorkshire-based veterinary surgeon, Karen Swindlehurst, using the test alone will not get eradication over the line.
She believes that the stigma around the disease and many farmers’ failure to even admit that they have the problem within their flocks, remain key obstacles to full eradication.
Perception of sheep scab
“Farmer mindset, where sheep scab is concerned, must be changed. The fundamentals of an effective eradication are now in place,” Swindlehurst said.
“The development of the new test is a game changer. But sheep farmers must use it effectively.
“Using the test without committing to the highest standards of flock health management will get us nowhere. So e.g., if new sheep are brought into an existing flock, they must be effectively quarantined from their new flock mates while testing is carried out.”
She stressed that only after the new arrivals have been tested, and found to be clear of scab, should they be mixed with other sheep. And all treatment interventions should be carried out as soon as possible.
Sheep scab is a notifiable disease in Scotland, but not in England. According to Swindlehurst, all sheep breeds are equally predisposed to the condition.
Effective treatment is an important component of any scab eradication campaign.
Currently, there are two methods of control. Sheep dip, which uses organophosphate-based chemicals, is one option. The second involves the use of macrocyclic lactone injectable products (MLs).
When a flock is treated with the MLs, ivermectin or doramectin, farmers are reminded that they do not offer any protection from re-infection.
Sheep have to be relocated to a clean pasture to prevent reinfection from the mite-infested environment. Scab lives in the location, off the sheep, for 17 days.
The ML moxidectin offers protection of 28 or 60 days depending on the concentration used. Some injectables require one treatment and some require two- farmers should to check the label for the correct protocol.
We are now seeing issues with resistance, following the widespread use of MLs.
ML-resistant scab mites were first identified in 2018 and sheep gut worm resistance to MLs is common in UK flocks.
As one of the five worming groups available for sheep, there is now a need to protect them and reduce the rate of development of resistance to manage roundworm burdens.
Cases of sheep scab mite resistance to the MLs were first confirmed in 2018, which has meant more and more farmers are now turning to organophosphates to protect and treat their flock.