Sheep scab, or psoroptic mange, is a form of allergic dermatitis caused by infestation of the skin surface with the scab mite Psoroptes ovis.
Sheep scab is considered to be the most contagious endemic ectoparasite disease affecting sheep in the UK. The disease is characterised by a yellow scab on the skin surface, and is accompanied by restlessness, scratching, wool-loss, bleeding wounds and loss of condition.
Sheep scab has been identified as one of the most important diseases for UK sheep farmers from both financial and welfare perspectives due to: the costs associated with reduced performance, preventative measures and treatment; coupled with the apparent distress, irritation and/or pain caused.
Sheep scab used to be thought of as a disease of autumn and winter but it is now common throughout the year, although the majority of outbreaks still occur between September and March.
Research at Moredun seeks to understand the mechanisms of immunity to the sheep scab mite, Psoroptes ovis, with a view to developing effective vaccines and diagnostic tests based on sound scientific rationale.
Sheep scab (Psoroptic mange) research at Moredun is supported by a number of funding bodies, including:
For further Information about Sheep Scab please see Moredun Newssheet 6.11 – Sheep Scab:
Our scientists regularly give talks and Moredun events and roadshows. Please see our events page for any forthcoming activities in this area or if you would like to arrange a speaker for an event please contact The Moredun Communications Team.
Diagnostic blood test
Infestation with the sheep scab mite, P. ovis can often be asymptomatic and in these cases the detection of mites in skin scrapings, the traditional diagnostic test, is unlikely to be successful. The inability to diagnose infestation before disease has spread through the flock is an obstacle to effective control and disease prevention. At Moredun we have developed an alternative method to diagnose infestation with sheep scab mites, which involves the detection of antibodies in blood. This diagnostic blood test can reliably detect the presence of P. ovis on sheep even before clinical signs of disease are evident (Fig 1). Therefore, the test will be of particular use as an aid to control the highly infectious mite and is available commercially via BioBest Laboratories. This ELISA test is based on the detection of antibody (IgG) with specificity to a single recombinant protein from P. ovis, Pso o 2. The test is highly sensitive (98.2%) and specific for sheep scab (96.5%) with no known cross-reactivity with other common parasite infections of sheep.
Potential applications of the test:
The optimum use of the test is to apply it at the whole flock or management group level in which case we recommend that a minimum of 12 sheep from the group (up to a group size of 2,000) are tested.
Mull eradication work
Based on the numbers of notifications since the introduction of the Sheep Scab Order (2010) Scotland, we were able to identify areas where sheep scab was either absent or present at very low levels. The data collected suggested that sheep scab was either absent from Mull or present at very low levels. If it was absent, then we sought to maintain that status and if it was present at low levels, then this would provide an opportunity to eradicate it and keep it out. To achieve this, Moredun Scientists, in conjunction with NFU Scotland and Mull Vets used the Moredun sheep scab ELISA on an island-wide basis (Isles of Mull & Iona) to determine whether or not flocks had sheep-scab. The study was spread out over two years and was completed in 2015. The first year involved applying the whole flock testing regime to as many flocks on the islands as possible and resulted in >700 samples being tested from >70 premises. No confirmed positives were detected and at this point the islands were assumed to be either free of sheep scab, or that scab was present at very low levels (Fig 2). The second year of testing was designed to maintain this status and involved the use of tups as sentinels of disease, by serologically testing them pre- and post-tupping. This resulted in a very different pattern of responses (more border line and positive tests) and resulted in the detection of an outbreak of sheep scab in a defined geographical area (Fig 2). The outbreak was isolated and controlled and animals on neighbouring properties were also tested with the ELISA; as well as any animals that were recently moved from/or to the affected area. No further outbreaks or cases were detected but this clearly highlights the need to be vigilant even in an area of relative low risk. This study has demonstrated the use of the sheep scab diagnostic test as a means of assessing disease status as part of a local eradication campaign.