Sentinel lambs were used to identify young Echinococcus granulosus infections in sheep, to provide an early indication of the progress of the South Powys Hydatidosis Control Scheme. Four sentinel lambs were purchased on each of 60 farms, from inside and outside the control area; they were examined when approximately six, 10 and 15 months of age. Gross examination, thin slicing of organs and histological examination of the lesions in the viscera revealed no E granulosus hydatid cysts in lambs born within the control area, whereas 25 per cent of the 15-month-old lambs from outside the area harboured E granulosus cysts (less than 1 to 2 mm in diameter). Lambs from E granulosus infected farms had significantly higher anti-E granulosus ELISA antibody titres than lambs from uninfected farms. It was concluded that within one year of beginning to treat dogs with praziquantel every six weeks the transmission of E granulosus to sheep had ceased. In contrast, this treatment did not prevent infections with Taenia hydatigena or T ovis; an examination of the 240 lambs revealed T hydatigena in 33.3 per cent of them, Tovis in 4.2 per cent, Dictyocaulus filaria in 12.1 per cent and Meullerius capillaris in 49.2 per cent.
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