Keep dipping to control outbreaks of sheep scab
As vets, we always keep an eye out for interesting disease occurrences in Britain and in our northern European neighbours. An outbreak of sheep scab in northeast Scotland caught my attention recently.
Sheep scab is a skin parasite that gets a lot of attention but not too much detail whenever it emerges. It is a notifiable disease which means we must inform the Department of Agriculture whenever we suspect or diagnose the disease.
Sheep scab is caused by a parasitic mite Psoroptes Scabii Ovis that feeds on sheep skin. It is a tiny mite with eight legs and two large biting jaws that penetrate the skin. The mite lives off the blood and lymph that oozes out of the bites.
A few interesting points with sheep scab is that an egg can hatch and grow and begin to lay more eggs in as little a time as nine days. One female mite will lay up to 90 eggs and live for up to 30 days on the sheep's skin. They love warm moist conditions and as the winter fleece thickens and the wetter autumn days approach, the fleece becomes a haven for mite development.
The parasite spreads by contact and can only be spread in two ways. One is close contact with an infected sheep or direct contact with any contaminated equipment.
This means that control is based on preventing infected sheep entering the flock or contaminated material coming onto the farm. This time of year farms will be taking in new breeding ewes or replacing stock rams.
Treatment involves dipping the incoming sheep and holding them in isolation from the rest of the flock to allow the dip to take effect. Injectable anti-parasitic agents can be used, but when it comes to specific treatment the best advice is always to contact your vet.
With sheep scab (as with many skin parasites) we take special care when dipping. With an outbreak of scab we always advise a double dip about 8-10 days apart. Follow the 4x100pc rule when dipping i.e. 100pc of the flock in each session; immerse 100pc of the sheep's body in the dip; keep the animal in the dip for 100pc of the recommended time (60 seconds) and dip at 100pc of the recommended strength of the dip mixture until the last animal has been dipped.