Genetic differences in host infectivity affect disease spread and survival in epidemics

Survival during an epidemic is partly determined by host genetics. While quantitative 10 genetic studies typically consider survival as an indicator for disease resistance (an 11 individual’s propensity to avoid becoming infected or diseased), mortality rates of 12 populations undergoing an epidemic are also affected by endurance (the propensity of 13 diseased individual to survive the infection) and infectivity (i.e. the propensity of an 14 infected individual to transmit disease). Few studies have demonstrated genetic 15 variation in disease endurance, and no study has demonstrated genetic variation in 16 host infectivity, despite strong evidence for considerable phenotypic variation in this 17 trait. Here we propose an experimental design and statistical models for estimating 18 genetic diversity in all three host traits. Using an infection model in fish we provide, for 19 the first time, direct evidence for genetic variation in host infectivity, in addition to 20 variation in resistance and endurance. We also demonstrate how genetic differences in 21 these three traits contribute to survival. Our results imply that animals can evolve 22 different disease response types affecting epidemic survival rates, with important 23 implications for understanding and controlling epidemics.