Sheep Scab remains a major concern for industry

Springtime sheep. Picture: Cliff Donaldson

Commodity watch by UFU policy officer David McClure

Sheep scab has been the subject of this commodity watch repeatedly every summer.  This is by no means a coincidence, as it is a real concern for members of our animal health and welfare committee. The pilot project which was delivered last year by Animal Health and Welfare Northern Ireland (AHWNI), has made great progress in raising the profile of this highly contagious disease and provided an insight into the practical challenges associated with the prevention, diagnosis, and treatment of sheep scab in Northern Ireland (NI). This funded project identified wide geographic spread in 106 flocks across the province and involved 39 different veterinary practices.

August sees the risk period for transmission of scab heighten, with breeding sheep being traded from farm to farm, often via marts. Therefore, the potential for infection to arrive on farm increases. There is a responsibility on buyers, sellers and marts to prevent the spread of scab. Visibly infected sheep should never be presented for sale either privately or at marts, until they are treated and fully recovered.

The scab mite is difficult to see with the naked eye making it challenging for purchasers of infected animals to identify that their new stock are already playing host to a potential nightmare which will soon unfold. Intense itching and wool loss are amongst the earliest signs visible to the farmer. However, this sometimes only occurs months after the initial infestation.

Farmers should remember that transmission can occur at other times of the year, and risk exists where infected sheep have shared a common space. Livestock trailers and scanning trailers are also common sources of infection. Thorough disinfection before and after use of such equipment will help to prevent spread.

Aside from the symptoms of scab which range from subclinical to severely symptomatic, and the highly contagious nature of the condition, the main concern from our committee members is around the limited number of effective treatment options available. Resistance has reduced the number of options available to effectively treat scab. As such, the industry must act responsibly to protect the treatment options which remain effective. The consequences of having no effective treatment method would devastate the NI sheep flock.

Fears of such devastation are replicated in Scotland. According to recent press, a Perthshire show cancelled all livestock due to a scab outbreak in the area. Beyond this, three neighbouring veterinary groups in Scotland have launched an initiative to fight scab in the area. A huge uptake has been reported and unlike the pilot which has just finished in NI, all costs lie with the farmers.

To avoid scab spreading to clean livestock, the best practice is to employ quarantine for all incoming stock. This facilitates a period of careful monitoring, where a treatment option can be selected if required. Blood tests can be used to confirm diagnosis where there is any doubt about the presence of scab on any animal. Purchasing animals privately from known sources will reduce the risk of picking up the condition indirectly, through shared handling pens and races.

Farmers can choose from using ivermectin based injectable products (administered under strict conditions) or plunge dipping with organophosphate (OP) products. It has been reported that injectables in some areas are somewhat ineffective due to resistance. The recent NI pilot project found that 25% of the flocks treated with injectable required subsequent dipping because of either resistance or a failure of injection technique. This concerning finding has also been mirrored by our neighbours in Scotland, according to recent reports.

It is critical that showers and jetters are not used to apply OP products, and to do so is illegal. By choosing to ignore this and continuing to shower with OP, scab mites would be exposed to a sub-lethal dose which not only ineffectively treats but encourages the development of resistance. This is a risk which cannot be taken given the limited number of treatment options that exist. It’s essential that producers act responsibly to protect these limited methods.

If you are in any doubt as to whether scab is present in your flock, consult with your veterinary surgeon immediately to confirm a diagnosis. Whilst an outbreak of this notifiable disease will restrict movements within the flock, these restrictions are very temporary and will be removed following appropriate treatment. There is no shame associated with an outbreak of scab on your farm. The only shame should be in not seeking appropriate help and guidance to promptly eradicate the condition.