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24/11/2017
BBC Radio 4

Sheep Scab – what it means for Brookfield

Writer, The Archers

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Alistair has confirmed that the Brookfield flock has sheep scab – and that it was almost certainly brought in with the refugee sheep David and Ruth are hosting after the floods in Worcestershire. Real-life vet Anne Gibbs explains the implications, treatment – and history – of this serious condition.

Sheep scab is a severe debilitating skin disease of sheep. It is caused by a mite, Psoroptes ovis, which burrows into and feeds off skin cells. Early signs of infection are very mild; maybe just a flick of an ear or occasional scratch, which can easily go unnoticed.

As mite numbers increase, sheep become so distracted with itching that they cause severe damage to their skin and rapidly lose weight. Skin damage leads to bacterial infection and, if left untreated, can cause death. Development of severe signs may take up to six weeks depending on individual flocks and level of introduced infection.

A single female mite will lay an egg every one to two days. Each egg takes around two weeks to reach adulthood  and adults live 40-50 days. The adult mite can live off its host sheep for up to 17 days, thus allowing infection to remain in pens, trailers, lorries and on equipment.

A farmer may inadvertently spread infection by trying to help another, if not careful about cleansing and disinfecting items that come into contact with sheep. This appears to be what has happened at Brookfield.

Treatment

Treatment options are either injectable products or sheep dipping, where all sheep must pass through a bath of an organophosphorus compound. Dipping is very effective but is labour intensive and carries risks to the operators as well as the environment.

Injectable products work well as long as strict guidelines are adhered to and every sheep on the farm is treated. A single escaped sheep can be responsible for a new outbreak of disease.

History

Sheep scab leads to poor fleeces, poor skins, poor carcasses and poor animal welfare. It clearly has a major economic effect . But it is not a new problem. Records show that Henry VIII suffered huge financial losses in the 1530s when the disease debilitated flocks held by the monasteries. He had hoped to gain substantial wealth from wool production but this was devastated by the mite.

Effective products and compulsory dipping led to the eradication of the disease in the 1950s, but it was reintroduced in 1973 following importation of infected sheep.

Legislation to control the disease using organochlorine products was successful until its withdrawal in 1984. The dip was replaced by organophosphorus compounds and used in compulsory dipping schemes until 1992. Concerns regarding human health and a reduction in cases led to deregulation that year.

Unfortunately, since that time there has been a rapid increase in the number of flocks affected and the disease is now found in every county of the UK. A Stamp Out Scab initiative has been running over the last 12 months. This advises farmers throughout the country on the best ways to recognise and treat the disease and to keep it out of their flocks if they are uninfected.

Eradication is again the aim of the industry.

Anne Gibbs is a partner in MacArthur, Barstow & Gibbs, a veterinary practice in Worcestershire

Learn more about sheep scab from DEFRA

 


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