The prevalence and distribution of sheep scab in Wales: a farmer questionnaire survey

I’ve authored my first paper! You can read the full journal article here if you have access to Wiley, or you can read on for a basic summary of the main results. The paper was co-authored by Dr. Hannah Vineer Rose and Prof. Richard Wall.

What is sheep scab?

Sheep scab is a skin infection which is (unsurprisingly) most commonly found in sheep, causing severe itching and self trauma which leads to tissue damage. It is caused by a non-burrowing biting mite called Psoroptes ovis.

Sheep scab is of high economic and welfare importance as it can result in a rapid loss of body condition and cause great discomfort to the sheep. In 2005, sheep scab was estimated to cost the UK sheep industry £8-14 million every year (Nieuwhof & Bishop, 2005).

Psoroptes ovis graphical abstract wordpress
A male Psoroptes ovis specimen, the causative agent of sheep scab

Prevention of sheep scab is extremely important; as well as being costly to farmers, the current treatment used (macro-cyclic lactones) can lead to resistance in other sheep parasites if over-used.

Sheep scab is usually spread through contact with other infected sheep; this makes it very important to isolate any new sheep being introduced to the flock.

Sheep-scab-615x346
Picture credit: County Vets

Outbreaks of sheep scab have increased 100-fold since it was deregulated in 1992 (this means it is no longer compulsory to use plunge dipping to prevent the infection), and since then it has been difficult to manage the disease.

How is sheep scab diagnosed?

The symptoms of scab are very similar to those seen in sheep with lice infestations. Therefore, it is important that farmers seek a conclusive diagnosis (ideally from a vet) so that the correct treatment is administered.

What did we do?

This study focussed on Wales as a previous study had already found that Wales has higher prevalence of sheep scab than England and Scotland. We carried out a postal survey of almost 1000 Welsh sheep farmers to investigate how prevalent sheep scab is in Wales now, around 10 years after the last study was carried out. We then used statistical analysis, GIS mapping and spatial analysis to determine the prevalence and distribution of sheep scab in Wales.

What did we find?

  • Scab outbreaks were reported to have occurred in 15.8% of farms during 2015
  • In the last 10 years, 29% of farmers claimed to have suffered from at least one scab outbreak, with 2.4% experiencing 6-10 outbreaks during this period
  • Most scab outbreaks occur between September-January (83%)
  • Scab outbreaks were clustered around Brecon (mid-Wales) and Bangor (North Wales)
  • Farmers using common grazing were significantly more likely to have suffered from a scab outbreak; 64.7% of farmers which use common grazing had experienced between 1-5 sheep scab outbreaks within the last 10 years
  • Many farmers (29%) did not use any quarantine procedures for bought in sheep, and 58.1% did not use any preventative treatments on sheep they introduced to their flock
  • Many farmers (69%) did not gain confirmation of their scab diagnosis, so there may have been some confusion between sheep scab and lice infestation
Fig 1 wordpress.jpg
Maps showing the distribution of sheep scab across Wales as reported by farmers. (A): Reported sheep scab occurrences in 2015; (B): Reported sheep scab occurrences in the last 10 years
Figure 2
Reported sheep scab outbreaks by month. We found that most scab outbreaks occur between September-January (83%), which coincides with the findings of other papers
figure-3-wordpress.jpg
Number of farms reporting having multiple outbreaks of scab in the last 10 years

Conclusions

The present study shows that common grazing is an important risk factor for sheep scab, and  that most farmers do not quarantine their bought-in sheep or use routine treatments to prevent against disease.  We’ve also found more evidence that sheep scab is very unevenly distributed, with a small number of farmers experiencing repeat outbreaks of sheep scab, and the majority of farms being scab-free most of the time.  The farms experiencing scab multiple times were clustered in several areas throughout Wales; these areas could be targeted for scab management efforts in future to help control a possible reservoir of scab-infected sheep.

What should future research focus on?

Further research is needed to develop localized management programmes, and it is important to focus on common grazing as these sheep are at higher risk from infection.

Further information about sheep scab

 

 

 

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