Parasitological examinations in sheep health management

Sheep are parasitised by a diverse range of internal and external parasites. The majority of adult helminths and many of the ectoparasites affecting sheep, are grossly visible to the naked eye due to their size. With internal parasites, however, observation and detection of adult stages is generally only possible on post-mortem examination of the appropriate organs and viscera. More often, the presence of parasites in the gastrointestinal tract, lungs and liver can be detected by parasitological examinations of appropriate samples, usually faeces, for the presence of their eggs, cysts or larval stages. This review focuses on the clinical and laboratory diagnostic approaches to a number of important parasitic diseases of sheep, in particular, parasitic gastroenteritis and the detection of species showing the presence of anthelmintic resistance, as well as other diseases, such as liver fluke and coccidiosis. The diagnosis of ectoparasite infections is generally much more straightforward, because of their size and location on the skin. However, misidentification can occur without appropriate experience in parasite identification. Accurate and correct diagnosis is fundamental to good parasite control, otherwise inappropriate or consequential, apparent treatment failures may occur.