Infectious diseases have a huge impact on animal health, production and welfare. Animal breeding schemes exploit heritable variation in host susceptibility, however, increasing evidence suggests that there may be additional genetic variation in host infectivity, i.e. the ability of hosts to transmit infections. We combined quantitative genetics and epidemiology to investigate the potential for enhancing genetic disease control by utilising host infectivity. A stochastic SIR (susceptible-infected-recovered) epidemiological model was used to simulate how disease dynamics are influenced by polygenic genetic variation in susceptibility and infectivity. Response to selection was calculated over 20 generations, exploring a variety of selection schemes differing in accuracy and intensity. Changes in epidemic risk and severity due to selection were compared between selection schemes considering only susceptibility, or combining susceptibility and infectivity. We explored how response to selection may be influenced by genetic correlations between susceptibility and infectivity, and finally, we present a case study for bovine tuberculosis, an infectious disease with global impact on cattle industry. Our results demonstrate that genetic selection considering both susceptibility and infectivity significantly accelerates disease eradication when compared to selection for susceptibility alone. For example, with moderate genetic variance, selection only on susceptibility required 13 generations to reduce epidemic risk by 50%, while combined selection for both susceptibility and infectivity required only 7 generations. With a favourable genetic correlation between susceptibility and infectivity, progress in the selection scheme was marginally improved by adding infectivity in the breeding goal. However, with a negative genetic correlation, including both susceptibility and infectivity reduced the delay due to indirect correlated responses in infectivity by 6 generations. In conclusion, our results suggest that to develop efficient genetic disease control strategies in the short- and long-term, genetic effects for both susceptibility and infectivity should be considered. Keywords: genetic gain, selection scheme, breeding objectives, breeding strategies, models

Smaragda Tsairidou, Osvaldo Anacleto, Kethusegile Raphaka, Enrique Sanchez-Molano, Georgios Banos, John Woolliams, Andrea Doeschl-Wilson

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Theory to Application 1, , 535, 2018
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