Chemotherapy of ovine fascioliasis: use of an analytical model to assess the impact of a series of discrete doses of anthelmintic on the prevalence and intensity of infection.

An analytical model of ovine fascioliasis is described. The model describes the essential features of the epidemiological patterns observed in the field and is used to assess the impact of a series of discrete doses of anthelmintic on the prevalence and intensity of infection in the flock. The reduction in prevalence after treatment with anthelmintics is shown to be critically dependent on the distribution of flukes amongst the ewes. The model is further used to define the optimum dosing times for a 2- or 3-dose regime. Model predictions concerning the optimum regime are in accord with usual treatment practices in the United Kingdom. The usefulness of analytical models of this kind in the assessment of disease control strategies is discussed.