21-EEID US-UK Collab: Long-Distance Dispersal and Disease Spread Under Increased Ecological Complexity

This project will focus upon infectious pathogens that have the capacity to transmit infection over a long distance. We will explore how this long distance spread is affected by a range of different characteristics that include the initial source of the outbreak, the way that the virus spreads and the spatial dispersal in the early stages of the outbreak. We will investigate this for a range of diseases of plants, livestock and humans that will include foot-and-mouth disease, West Nile Virus, sudden oak death, cucurbit downy mildew, hop powdery mildew and wheat stripe rust.
The proposed research will add to our knowledge of disease transmission and spread by incorporating epidemic complexities that are not always considered in epidemic models and theory. The work will improve our understanding of disease spread, and is crucial to predicting the spread of epidemic invasions and designing disease control strategies. The work is potentially transformative as it will provide a rare opportunity to test hypotheses in natural and manipulative field experiments, and because the applicability of a broad diversity of plant, animal, and human pathogens with fat-tailed dispersal kernels will be rigorously evaluated via the interdisciplinary modeling efforts. Conclusions should apply over a very wide range of spatial scales due to the nature of these pathogens that have the potential for long-distance dispersal, and because empirical data used in the project will have been derived over varying spatial scales.
Several participants have long-term knowledge of their disease system that will enable them to investigation optimization of mitigations in terms of policies, societal impacts, and epidemic spread. For foot-and-mouth disease, indirect costs (those beyond direct loss of livestock) as a result of livestock movement restrictions, export bans and closure of the countryside that can affect tourism will be evaluated. The disparity between local costs (to individual farms) and nationwide costs (to the economy), whereby certain individuals may be disproportionately affected by a given intervention policy will also be evaluated. Through collaboration with the Oregon Department of Forestry, the sudden oak death group will sponsor workshops on how new research influences disease management, value of timber, loss of trade, cost of management, etc., as well as impacts on Native American and Hispanic communities. The West Nile Virus group will be involved with "Training the Trainers" activities relative to optimum management of that disease. The cucurbit downy mildew and hop powdery mildew groups will consider optimal control policies that are identifiable when spatial and temporal dynamics of epidemics are considered. They will do this by formulating a linked epidemiological and economic model of spread of hop powdery mildew and cucurbit downy mildew that considers management interventions that delay disease onset, therapeutics that reduce the rate of disease spread, and differential susceptibility of hosts in a landscape with multiple disease epicenters with and without collective actions of individuals. The wheat stripe rust group will continue their long-time associations with wheat growers of Oregon and applying ecological genetics to the sustainable management of wheat diseases.
The outcomes of this grant will provide vital insights into the risks associated with these pathogens and will help to inform contingency planning should these viruses emerge in the future.

Much of the extant theory regarding epidemic spread is understandably anchored in simplified conditions of single outbreak sites, genetically uniform hosts, and deterministic epidemic responses. The global objective of this proposal is to determine how epidemic outbreaks resulting from long-distance dispersal (LDD) of pathogens is influenced by more complex epidemiological conditions. This will be done by addressing four hypotheses: 1. Locations of multiple sources of epidemic outbreak can be imputed from population dynamic models. 2. Ecologic spillover effects influence the spread of LDD epidemics in a predictable manner, and strongly influence observed relationships between disease spread and host diversity. 3. More robust predictions of epidemic spread can be obtained by combining deterministic and stochastic variables influencing pathogen dispersal to produce a prediction cone of uncertainty that varies over time. 4. A unifying framework of epidemic models emerges across LDD diseases incorporating taxonomically diverse hosts and pathogens and time-variable environments.
These hypotheses will be addressed with a set of hosts and pathogens of highly divergent taxonomy, but which share the common characteristic of potential for LDD. The model systems include foot-and-mouth disease of livestock, West Nile Virus, sudden oak death, cucurbit downy mildew, hop powdery mildew, and wheat stripe rust. The model systems were carefully chosen based on a history of strong prior work, high quality data for parameterizing models, and extensive previous modeling efforts. Further, for five of these systems, observational tests of hypotheses from natural experiments can be made utilizing extensive data collected during actual epidemics. Two of the systems will also be used in manipulative experiments to test imputations of multiple outbreak sites.