Viral transmission between host species can harm public health, conservation efforts, and the global economy. I examine the determinants and dynamics of viral host jumps by identifying three steps required for viral emergence in a novel host species: encounter (contact between infectious virions and a potential new host species), infection (replication within an individual of a novel host species), and propagation (transmission between individuals of a novel host species). I first lay out a general framework for addressing the interaction of ecology and molecular biology that determines whether a host jump will occur. I then focus in turn on the determinants of infection once encounter has occurred and the dynamics of propagation following infection. I analyze the effect of three specific viral characteristics (site of replication, genome segmentation, and genomic material) on the ability of livestock viruses to infect human hosts. I find that (1) the ability to complete virion replication in the cytoplasm without nuclear entry facilitates viral host jumps, (2) genome segmentation has a non-significant but consistently positive effect on host-jump ability, and (3) having an RNA genome may facilitate host jumps though the effect is equivocal in the dataset used.; I next address the dynamics of propagation within a novel host species. I describe a general phenomenon, epidemic enhancement, whereby repeated viral introduction into a novel host population can produce longer and larger epidemics than observed upon initial introduction. Finally, I show that epidemic enhancement drove Nipah virus emergence in domestic pig populations in Malaysia, which ultimately led to widespread human infection throughout the country.; Overall, I have demonstrated that general principles and mechanisms do underlie cross-species viral transmission. As we continue to unravel the determinants and dynamics of viral host jumps, we will improve our ability to predict, prepare for, and respond to future threats. |