Abstract

Fasciola hepatica, one of the causative agents of fascioliasis, infects animals and humans globally causing mass morbidity and expansive drains on the agricultural economy. Its complex lifecycle, requiring an intermediate snail host, makes it difficult to control with levels of resistance to the drugs used to treat it increasing. This research aimed to provide a global overview of F. hepatica prevalence, its distribution and how it is managed in the UK, and an insight into the reaction of an intermediate host to infection. The meta-analysis of global bovine and ovine fascioliasis prevalence indicated higher levels in temperate areas with moderate levels of precipitation, decreasing prevalence over time, and a higher infection rate in sheep than cattle. However high heterogeneity within the dataset means these conclusions must be interpreted with care. The questionnaire and accompanying livestock faecal egg count test for UK farmers indicated that many of the suggested control strategies are being used, such as rotating flukicides, targeting treatment, and limiting livestock access to areas of pasture at high-risk of infection. The presence of snail habitats, with these used as a drinking source, and grazing animals at high fluke risk periods during the year were the most suitable predictors of fluke presence on the farm, with a predicted prevalence of 24.42%.In addition, it was also observed that F. hepatica infection risk increased the further west the farm was located. When looking at the response of an intermediate host of F. hepaticato infection, namely Lymnaea stagnalis, both protein and phenoloxidase levels were downregulated with infection, with no effect of treatment on longevity, egg laying capacity, nitrate concentration, or haemocyte count. The prevalence study reiterates the importance of surveillance with an integrated approach of monitoring resistance and prevalence, feeding back the best methods of control to those with livestock, and the collaboration of parasitologists and climate change scientists required to help control this increasing burden. To successfully control this disease the interactions between the snail host and the parasite is required, with the immunological study carried out here aiming to kick-start this research. Novel control mechanisms are required which can only be developed with enough knowledge of this complex snail-trematode interaction. With climate change and drug resistance exacerbating the global fascioliasis problem it is imperative that research continues into the surveillance, management, and control of this parasites at all stages of its life cycle.