Genetic differences in host infectivity affect disease spread and survival in epidemics O. Anacleto1, S. Cabaleiro2, B. Villanueva3, M. Saura3, R.D. Houston1, J.A. Woolliams1, A. Doeschl-Wilson1 1The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Division of Genetics and Genomics, Midlothian EH25 9RG, UK osvaldo.anacleto@roslin.ed.ac.uk (Corresponding Author) 2INIA, Departamento de Mejora Genética Animal, Crta. La Coruña Km 7.5, 28040 Madrid, Spain 3Cluster de la Acuicultura de Galicia (CETGA), Spain Genetic analyses of infectious disease data usually focus on host resistance to becoming infected or host ability to survive when exposed to infection. Increasing evidence however shows that risk and severity of disease outbreaks also depend on infectivity, which is the host ability to transmit infections. These traits may be under genetic control and correlated, but empirical evidence for this is currently sparse as appropriate data are lacking. This hampers introduction of effective breeding techniques that reduce disease spread. We developed a large scale transmission experiment using 1800 fish, which provided suitable epidemic data for genetic analyses of infectivity, resistance to becoming infected and also tolerance to infection (ability to survive despite being infected). Scuticociliatosis, caused by the parasite Philasterides dicentrarchi, was used as a disease model. Since genetic studies of infectivity require natural transmission of the parasite, unrelated families of full-sibling fish (shedders) were artificially infected and distributed into 72 tanks, which in turn contained non-infected naïve fish (recipients). Disease outcome was observed by daily recording of infected and dead fish. Differences in Kaplan-Meier curves for recipient time to infection pooled by shedder or recipient families strongly suggested genetic variation in shedder fish infectivity, as well as in resistance, whereas evidence for genetic variance in tolerance was weak. Bayesian generalized linear mixed models fitted to daily counts of recipient fish with visual signs revealed that fish were on average 2.4 times more likely to become infected when exposed to the most infective shedder family compared to the least infective family. These results provide the first evidence for genetic variation in infectivity and offer new opportunities for implementing novel disease traits into animal breeding strategies to reduce infectious disease spread in livestock population. Keywords: animal breeding, disease resistance, host infectivity, aquaculture

Osvaldo Anacleto, Santiago Cabaleiro, Beatriz Villanueva, Maria Saura, Ross Houston, John Woolliams, Andrea Doeschl-Wilson

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology - Disease Resistance 3, , 500, 2018
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