Russell, Vinca N. L. (2013) Combining genetics and epidemiology : a model of footrot in sheep. PhD thesis, University of Warwick.

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Abstract

The interaction between host genetics and epidemiological processes in ovine footrot
was investigated using a combination of data analysis and simulation modelling. The
study’s aims were to determine the potential for genetic selection to be used to
reduce the prevalence of footrot in the UK and to assess different strategies for use of
conventional epidemiological interventions.
A stochastic simulation model was developed, incorporating host genetics for traits
controlling footrot resistance, bacterial population dynamics, sheep population
dynamics and epidemiological processes. Sensitivity analysis of the model showed
survival time of Dichelobacter nodosus in the environment and infection rate were
the key determinants of disease outcomes.
Antibiotics were predicted to be the most effective conventional control method,
reducing prevalence of footrot to 1-2% when administered promptly. Pasture
rotation, selective culling and vaccination were all predicted to reduce prevalence but
to a lower extent.
Analysis of field data confirmed the likely role for some degree of host genetic
control of footrot resistance, i.e. resistance appears to be lowly to moderately
heritable. Using the simulation model it was then shown that genetic selection could
be effective at reducing footrot prevalence. In combination with antibiotic treatment
or pasture rotation elimination of footrot from an individual flock could be achieved.
Genetic selection was predicted to be effective at reducing prevalence and improving
resistance but the choice of selection criteria impacts the results seen. It is likely that
progress would be slower in field situations because footrot traits would be diluted
by simultaneous selection for other traits affecting profitability.
Field studies are required to determine optimal combinations of interventions and
genetic selection and to validate modelling outcomes. Combined data from
longitudinal disease observations, genetic information and bacterial samples are
necessary to address current knowledge gaps and to further advance understanding of
host and disease processes in ovine footrot.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QR Microbiology > QR180 Immunology S Agriculture > SF Animal culture
Library of Congress Subject Headings (LCSH):	Footrot in sheep -- Simulation methods, Footrot in sheep -- Epidemiology, Footrot in sheep -- Susceptibility, Sheep -- Immunology -- Genetic aspects, Host-parasite relationships -- Genetic aspects
Official Date:	June 2013
Dates:	Date Event June 2013 Submitted
Institution:	University of Warwick
Theses Department:	School of Life Sciences; Roslin Institute
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Green, Laura E.; Medley, Graham, Bishop, S. C. (Stephen C.)
Sponsors:	Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC); Pfizer Inc.
Extent:	xiv, 210 leaves : illustrations.
Language:	eng

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