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Lookup NU author(s): Zoe Berk, Professor Ilias Kyriazakis
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Implications As the emergence of parasite resistance to anthelmintics is a serious issue in grazing ruminants (Sutherlandand Leathwick, 2011) the development of effective control strategies to reduce the rate of selection for anthelmintic resistance is an imperative. Simulation models that enable the investigation of the consequences of such strategies may constitute a cheap and faster alternative to experimentation: here we describe the development of a novel model for cattle.Introduction Gastrointestinal (GI) parasitism poses a major challenge to the health, welfare and productivity of cattle. Ostertagia ostertagi is one of the most prevalent GI parasites of cattle worldwide and is responsible for health challenges to cattle in the UK. The objective of this work was to develop a deterministic, dynamic model to predict the dynamics of O. ostertagi and consequences to the host of different levels of infection in first season grazing cattle.Material and methods The model stems from the principles developed by Laurenson et al. (2011) to represent ruminant host-GI parasite interactions. Initially, the growth of a healthy calf was simulated, taking into account genotype and nutritional conditions. Subsequently, the effects of O.ostertagi infection were simulated using published data sets to estimate parameters. The effect of the immune development on within-host dynamics of the parasite was assumed to be a function of larval exposure, and the subsequent phenomenon of parasite-induced anorexia was assumed to occur as a result of the rate of immune development. Abomasal damage was assumed to cause plasma loss (Fox, 1993).Worm egg production was a function of worm number and fecundity which, in turn, showed density-dependent constraints. Simulations were run over 200 days for three infection doses of 3,500, 7,000 and 14,000 infective larvae administered daily.Results Worm burdens were greatest at higher challenge doses, but once immunity was developed the decline was steeper for higher challenges (Figure 1). Worm burdens never reached zero even when immunity was fully developed. Egg outputs (data not shown) were a reflection of the worm burdens; however the relative differences between challenge levels were smaller, due to the density dependence effects. A reduction in food intake was observed for all infection levels; with the reduction being greater for larger challenges. The point at which the maximum reduction in intake was observed was earlier for higher infection levels and all intakes returned to levels similar to a healthy host towards the latter stages of infection. As challenge level increased the losses in weight gain were disproportionately larger than the increase in challenge (Figure 2).Conclusion A model simulation has been developed which has behaviour consistent with our understanding of GI parasitism in sub-clinically infected calves. Predicted features of interest are: (i) the increased rate of decline in peak worm burdens for greater challenge doses, reflecting the greater immune response, (ii) smaller differences in egg outputs than worm burden with changing challenge level, due to the density-dependence effect, and (iii) disproportionately large body weight losses with increasing challenge level, due to greater parasite-induced anorexia and the inability to meet increased nutrient demands for repair. To ensure confidence in the model it must be validated against published literature studies.Acknowledgments The authors acknowledge funding from BBSRC and MerialReferencesFox, M.T. 1993. Veterinary Parasitology 46, 143–58Laurenson, Y.C.S.M., Bishop, S.C., Kyriazakis, I. 2011. The British Journal of Nutrition 106, 1023–1039.Sutherland, I.A., Leathwick, D.M. 2011. Trends in Parasitology 27, 176–181
Author(s): Kyriazakis I; Berk Z; Bishop S; Forbes A
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: Advances in Animal Biosciences - Science with Impact - BSAS
Year of Conference: 2015
Pages: 179
Print publication date: 01/04/2015
Online publication date: 01/03/2015
ISSN: 2040-4700
Publisher: Cambridge University Press
URL: http://dx.doi.org/10.1017/S2040470015000035
DOI: 10.1017/S2040470015000035
Series Title: Advances in Animal Biosciences
