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 and a losing cost to the UK sheep industry of over £8 million per year.
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.
The mite is just about visible to the naked eye and can only remain viable off the host (sheep) for 15-17 days. Sheep with early infestations may show no signs, at these early stages, sheep can look perfectly normal and can unknowingly be introduced to a flock.
Later stages of infestation see high mite numbers and the lesions spread. Scab mites cannot feed on the hardened scab so they are forced to go to the edge of the lesion, making it spread out. The mites tend to congregate on certain areas of the body such as the groin, between the fore legs, inside the ears, in between the cleats of the hoof and in the wrinkle skin of the scrotum of rams. The life cycle of the mites takes less than two weeks so it can accumulate rapidly in a short period of time.
Do not guess if you suspect your sheep have scab. Contact your vet and get a diagnosis before deciding what action to take. Skin scrapings can be examined, or a blood sample can be tested to detect antibodies to a specific protein found only in the sheep scab mite. The advantage of the blood test is that it can detect scab mite infestation at an early stage, before the onset of clinical symptoms. Unfortunately the blood test is not available in Northern Ireland at the minute.
Quarantine treatment options are currently limited to organophosphate plunge dipping or injection with macrocyclic lactones. All treatments should be administered strictly according to the manufacturers’ instructions. The selection of a suitable treatment for sheep scab may depend on integration into the flock’s current worming strategy. Dip-baths must be accurately calibrated and sheep should be weighed before treatment with an injectable. Bio-security is one key area to help prevent scab from getting into your flock. Quarantine is key for incoming stock and you should also monitor the source for the incoming flock.