Using Caenorhabditis viruses to identify the ecological role of spillover outcome on the evolution of disease emergence

The emergence of new infectious diseases can have important consequences for the health of many organisms. Most emerging diseases arise when a pathogen of one host species infects a new host species and then evolves the ability to replicate well within hosts and transmit well between hosts. When the pathogen transmits itself well enough to remain in the new host species indefinitely, this is referred to as a disease emergence event. This phenomenon is also known as a "host jump". Preventing host jumps depends critically on identifying traits associated with disease emergence so that actions can be taken early to stop the spread of the disease. However, knowledge of the factors that facilitate or prevent host jumps is limited. This research seeks to identify the conditions following exposure that determine risk of emergence. The findings of this research will have direct relevance for conservation efforts, food security and human health. The researcher will also widely disseminate the knowledge gained from this work to the public. Pathogens can be classified by spillover potential. SP1 pathogens are incapable of infecting new hosts. SP2 pathogens can infect new hosts but not transmit. SP3 pathogens can infect new hosts and transmit but not well enough to persist. Pathogens in any of these three categories could presumably, under the right circumstances, evolve to become established pathogens. Current theory assumes that emergence risk is highest for SP3, followed by SP2, followed by SP1 pathogens. Despite these theoretical predictions, little empirical work has explored how emergence risk varies by spillover class. This research will use experimental and theoretical approaches to challenge this theory. It will identify the underlying mechanisms that explain variation in emergence success using a novel experimental system (Caenorhabditis hosts and viruses native to C. elegans and C. briggsae). The Caenorhabditis-virus system allows for pathogen transmission in large, replicate host populations. Furthermore, preliminary data has shown that host-virus combinations span the range of SP1, SP2, and SP3 pathogens. Specifically, the research will first characterize virus dynamics following exposure of Caenorhabditis hosts to their non-native viruses. Second, the work will characterize the evolution of pathogens following exposure of Caenorhabditis hosts to their non-native viruses. Finally, the work will develop mathematical models connecting virus dynamics to host jump success. This project is jointly funded by the Division of Environmental Biology (Evolutionary Processes Cluster) and the Division of Integrative Organismal Systems (Symbiosis, Infection and Immunity Program). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.