Rose Young BVM BVS MRCVS, Molecare Veterinary Services
Scab is a parasitic disease of sheep unfortunately familiar to many farms. It is caused by a mite, psoroptes ovis which specifically affects sheep, and is responsible for considerable economic losses and welfare implications in parts of the UK. In England and Wales, local authorities can enforce treatment in a flock where disease is suspected and no action is being taken. In Scotland, scab is a notifiable disease which must be reported to APHA. This article provides an overview of the condition, advice on diagnosis, treatment and best practice for biosecurity and control.
Mites survive for relatively long periods off the host (up to 17 days) and can therefore be spread via contaminated objects in the environment as well as the primary route; direct nose to nose contact between animals. Early infection, when mite numbers are low, may be virtually undetectable. As parasite numbers rise, the classic signs begin to appear;
- Rubbing/nibbling
- Severe itching
- Head shaking/foot stamping
- Fleece loss
- Scab/sore formation
Once a sheep is heavily infected, significant loss of condition, ill thrift and even seizures and death can occur. Often animals within a flock will be at varying stages of infection.
Diagnosis
Correct diagnosis of scab is vital to ensure that appropriate treatment is initiated. Scab is indistinguishable by eye from other conditions causing itching in sheep; treatment targeted at lice will be ineffective against mites and vice-versa, potentially resulting in wasted time and money. Where disease is already suspected, a quick skin scrape taken by your veterinary surgeon from the edges of an established scab lesion and examined under the microscope should yield a diagnosis. A blood test is also available to detect antibodies produced by the sheep in response to infection; this method may provide a diagnosis earlier in disease before lesions appear, if skin scrape is insufficient, or as part of a quarantine protocol. However antibodies are only detectable approximately two to four weeks after infection, so timing of testing and quarantine in the interim period is crucial.
Treatment
If scab is diagnosed in your flock, the entire group of in contact animals will require treatment to eliminate infection. This may include stock from neighbouring farms if boundaries are not very secure. The treatment will need to remain effective for long enough to cover the possible re-infection period of up to 17 days while mites remain alive in the environment. Sustainable Control of Parasites in Sheep “SCOPS” is an organisation that provides some excellent practical advice on all aspects of parasite management in sheep, with a focus on preventing further wormer resistance developing in our industry. A downloadable table available from their website sets out some treatment options, which should be discussed with your vet to decide on the most practical and suitable option for your situation.
Biosecurity and control
Scab diagnoses are increasing in England and Wales, sheep farmers are therefore strongly advised to protect their flocks and maintain biosecurity wherever possible.
- Maintain secure double-fenced boundaries
- Maintain a closed flock
- Avoid handling areas/equipment shared with other sheep
- Test/treat and quarantine purchased animals
- Investigate all cases of itching or loss of fleece promptly
Identifying the source of infection, for example purchased animals, neighbouring sheep or use of summer grass keep is an important step in preventing reinfection. Discuss the options with your vet who can help you tailor a flock health plan and biosecurity measures to your farm and make sure the biggest risk areas are covered.
For more information phone Molecare Veterinary Services on 01392 872934.
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