Anthelmintic suppression of Fasciola hepatica infections in sheep

In an experiment to examine the use of anthelmintics to suppress the faecal egg output of Fasciola hepatica from sheep and reduce the prevalence of infection on a sheep farm with a history of chronic fasciolosis, triclabendazole was administered four times annually for three years. During the first year, treatments in April, June, August and October failed to reduce the prevalence. In the subsequent two years the first annual treatment was brought forward to January and February, and the prevalence was reduced by 74.6 and 69.7 per cent, respectively. The mean plasma gamma-glutamyl transpeptidase concentration of the flock was significantly reduced from 55.9 units/litre before the experiment to 40.9 and 38.3 units/litre. In the second and third years the packed cell volume increased from 0.29 litre/litre to 0.36 litre/litre and the percentage of infected Lymnaea truncatula decreased to zero.