PC Sheep Scab 2020 FINAL


Sheep Scab

How does it spread? Sheep to sheep

Most commonly, it is transferred between sheep through direct contact. It is important to recognise that this mite can survive off the host and maintain infectivity for up to 16 days in buildings, on posts or gates where sheep have been itching and scratching or on sheep-handling equipment. As a result, other sheep may potentially become infested when rubbing against these same objects. Farm to farm Sheep scab can be spread from farm to farm through the purchase of infested sheep, many of which may be sub- clinically infested (not yet showing clinical signs of disease such as itching or scratching) or through the borrowing of sheep-handling equipment which has been used on infested sheep within the previous 16 days without adequate cleaning. The use of communal or shared grazing areas is also a potential risk factor for infestation when sheep from Although the species that affects cattle is considered to be the same species that affects sheep, there is limited transfer of the mite between cattle and sheep . Indeed, the scab mite strain that is found on sheep tends to feed on skin oils which contrasts with the mite strain found on cattle, where red blood cells form an important part of the diet. If it is suspected that cattle are affected by P. ovis , this should also be reported to the local Veterinary Inspector. How is sheep scab diagnosed? Sheep scab is commonly diagnosed based on clinical signs such as itching, scratching and nibbling. Other ectoparasites such as lice must also be considered when investigating the potential cause(s) of these clinical signs. To confirm a diagnosis, both skin scrapes and samples of wool should be collected from the edges of active lesions and examined for the presence of ectoparasites such as mites and lice. A blood test has been developed in the UK which can be used to detect sub-clinically infested animals. Antibodies detectable in blood are produced by the sheep from two weeks after exposure to the sheep scab mite. This test can be particularly useful, as in many cases purchased sheep that are not showing any clinical signs are a means of introducing this mite into a new flock. Animals that are brought onto a farm should be quarantined and treated if necessary, before mixing with the main flock to prevent spread of mites. Control and treatment It is important to recognize that although the entire life cycle of the scab mite is spent on the sheep, these mites can also survive off the host and maintain infectivity for up to 16 days . Thus, fields or sheds which previously housed sheep scab-infested animals can only be considered mite-free areas if these locations have been kept free of sheep for more than 16 days. The treatment of sheep scab involves the use of either dips (e.g. organophosphate-based diazinon or the synthetic pyrethroid cypermethrin) or injectable macrocyclic lactone anthelmintics (wormers) (e.g. ivermectin, doramectin and moxidectin). There are important differences in administering the treatment and the speed of action between dips and injectable treatments. There are also differences within the macrocyclic lactone wormer group as regards their persistence of action. These differences are outlined below in Table 1 below. affected flocks can potentially come into contact with sheep from unaffected flocks. Is there transfer of mites between cattle and sheep?


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