It is impossible to be certain if a sheep has sheep scab without a diagnosis. Yet thousands of sheep are treated every year on the basis that people think they know. Getting it wrong it will waste your time and money, risk the health of the sheep and result in unnecessary use of products. It will delay the animal recovering, resulting in financial losses, and increase the risk of resistance in the future.
What is sheep scab?
Sheep scab is a major source of economic loss in affected flocks and is a serious threat to sheep welfare. Infestations can be very debilitating with significant loss of condition, secondary infections, hypothermia and eventually death. Sheep scab is a notifiable disease in Scotland.
Sheep scab is actually an acute or chronic form of allergic dermatitis caused by the faeces of the sheep scab mite (Psoroptes ovis). The mite is just about visible to the naked eye and can only remain viable off the host (sheep) for 15-17 days. There are no other hosts for these mites, although they can remain viable on cattle. The lifecycle takes 14 days.
Sheep scab can be contracted via any contact with live mites. This is usually through sheep-to-sheep contact at market, in livestock lorries or areas such as shared rubbing posts. However, shearing combs and cutters, contaminated clothing, tags of wool or scab attached to brambles bushes etc. can also spread scab.
Sheep scab is mainly a winter disease with most cases occurring between September and April, although a significant number of cases do occur in the summer months, particularly on full fleeced animals such as lambs and the ‘ridges’ of longer fleece on poorly shorn sheep.
During the early stages of sheep scab, infestations are not obvious and animals often appear clinically normal. Early disease involves low mite numbers and very small lesions that are virtually undetectable. Sheep with early infestations may show no signs or simply be restless, rubbing against fence posts, have soiled and stained areas of wool toss their heads or have deranged or tags of fleece. 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. Rubbing and head tossing becomes more and more excessive, areas of wool loss may appear often with open, bleeding wounds. Sheep rapidly lose condition and serious cases will start fitting.
Get a diagnosis
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.
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