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Title: Predicting temporal changes in Fasciola hepatica abundance from climatic variables
Author: Smith, Daniel Barnaby
ISNI:       0000 0004 6059 9852
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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Fasciola hepatica is an economically important parasite of sheep and cattle. The life cycle of this parasite includes freeliving stages and an intermediate snail host (Galba truncatula). In the past, several statistical models have been developed to predict how climatic factors, specifically temperature and rainfall, affect parasite abundance. However, these models were built under historic climate conditions, or for a specific geographic region, and are not well suited to predict how the epidemiology of infection might change in situations of global climatic change. The primary objective of the work described in this thesis was to develop a mathematical model of the life cycle of Fasciola hepatica that, for the first time, captures the seasonality of the parasite and can be used to predict parasite abundance under the varying conditions of climate change and alterations in farm management practices. To build the model, experimental studies were conducted to increase the available data on parasite development and survival in the environment. The experimental work focused on the effects of temperature and water availability on parasite eggs and metacercarial development and survival. The survival of parasites at low temperatures suggests that overwintering of parasites on pasture is very possible. The differential equation model developed focused solely on the freeliving stages of F. hepatica and runs on daily temperature and rainfall (rainy day) data. The model was validated against data from published longitudinal studies and passive disease surveillance data. The limited data available to validate this type of model made it impossible to validate the model in a sufficiently robust manner. From the validation studies, it appears that the model is good at predicting the seasonality of the parasite but performs less well at predicting differences in peak abundance between years. The model predicts that, under two different greenhouse gas emissions scenarios, the abundance of F. hepatica will increase dramatically in future, with more than twice the number of metacercariae currently seen between August and October, and significantly more pasture contamination between June and December. The effects of dosing animals at different times of the year was also investigated, Under historic conditions, in the United Kingdom, a single dose of an appropriate helmintic treatment administered to animals in March will not reduce the number of metacercariae seen in the autumn, but a significant reduction results if an appropriate anthelmintic is administered in May. Greater metacercariae pasture contamination predicted under future climate projections will necessitate changes in farm management practices aimed at limiting transmission, which is predicted to occur earlier in the year.
Supervisor: van Dijk, J. ; Williams, D. ; Morgan, E. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral