What is Sheep Scab?
Sheep scab is a endemic disease caused by Psoroptes ovis, more commonly known as scab mites. Scab mites defecate on the skin which causes an allergic reaction. With a short life cycle of only 14 days, scab mite populations can increase fast and can infect an entire flock, even more so when kept indoors and in close proximity. The mite can survive for up to 17 days off the sheep but must use the sheep to complete their lifecycles.
Psoroptes ovis is an Ectoparasite
Sheep Scab is caused by the ectoparasite Psoroptes ovis. Ectoparasites are simply parasites that live on the outside of an animal like a tick or blowfly. In comparison to endoparasites that live internally, like worms or coccidia. As is common husbandry practice, sheep fleeces are left to grow over the colder months to keep the animals warm. Some farmers may also choose to house their animals indoors too. Although this keeps the sheep warm and unexposed to the elements, it does produce the perfect home for some lovely little critters!
How do sheep get sheep scab and what are the signs?
Sheep scab is spread via contact, mainly via sheep to sheep but infected surfaces can also pass the parasite on. Similarly, mites can be spread by contaminated clothing on handlers and shared equipment such as shearers. The mites can also live within the wool left by sheep that have been scratching on surfaces providing another source of transmission.
With small burdens there may be no observable signs of infestation. This means infected animals may be introduced to a new flock unknowingly. In sheep with moderate burdens, obvious signs begin to occur such as: restlessness, scratching or rubbing against gates/posts/fences/hedges, a soiled back end, head tossing and some missing patches or fleece or fleece tags dangling. With more severe cases, sheep may exhibit excessive head tossing, rubbing, excessive wool loss with some bloody lesions from scratching on surfaces. Left severe and untreated, eventually body condition will deteriorate fast and an animal can undergo seizures and death.
How do I know if my sheep have sheep scab and what do I do next?
To diagnose sheep scab, you can ask your vet to take skin scrapes or a blood sample for ELISA testing. A skin scrape is not always suitable for detecting low burdens, however a blood test should be able to do this. We can examine skin scrapes at RRL and perform a parasite ID test.
Once diagnosed, find out where the mites originated from and try to reduce contact. You may also want to think about reducing contact of the infected sheep with any neighbouring flocks. You can treat sheep scab with two types of medication: organophosphate plunge dips and injectable endectocides. Please do not use these if you have not confirmed sheep scab, as you will waste money. If you are unsure at all, please contact your vet.
Ensure you are giving the right product for your sheep, at the right dose rate with the correct technique. Make sure you’re aware whether the treatment you’ve chosen is one or two doses, as one may be ineffective and cause resistance. Will you need to also move the animals to somewhere clean so they don’t become re-infected?
If you have treated your sheep and symptoms persist, you must contact your vet and not re-administer treatment. This could be a resistance issue and re-treating may make it worse and/or waste your money. More detailed information and guidance can be found on the SCOPS website.
Sheep mite infestations can be very severe and cause huge economic burden to a farmer, as well as the welfare implications on a flock. Please note that sheep scab is a notifiable disease in Scotland so please be sure to report this to APHA here.