School of Aquatic and Fisheries Sciences
Non Technical Summary
The emergence of pathogens into new hosts and geographic regions is a widespread problem for a variety of wildlife, human, and agricultural diseases. Although pathogen emergence has been broadly studied in many terrestrial systems, there is relatively little knowledge of the transmission processes that drive aquatic pathogen emergence. Due to expansions of, aquaculture, aquatic habitat loss, fisheries harvest, and aquatic species conservation, the emergence of pathogens in aquatic ecosystems has become a critical issue. As such, there is increasing demand from aquatic animal health managers for tools to predict pathogen disease outbreaks and emergence. Aquatic pathogens have unique transmission properties and understanding emergence events in aquatic hosts requires information on a variety of ecological, environmental, host, and viral factors. Here we propose to develop informative models of transmission dynamics for the salmon pathogen infectious hematopoietic necrosis (IHN) virus. We will focus on documented viral emergence and displacement events that have occurred in Pacific Northwest river systems by testing viral genetic types associated with these events in relevant fish host populations that vary in IHN virus susceptibility. This will involve utilizing a novel integrative approach that combines process, data, and transmission network models, informed by epidemiological and ecological data, in vivo viral fitness experiments, and genetic and immunological markers of host susceptibility and phenotypic plasticity. Our goal is to elucidate general principles and ecological processes that drive IHN virus transmission, emergence, and displacement. Results from this project will have impacts on the economic health of rural and tribal communities, as well as State- and region-wide fish hatchery programs, by improving their return on salmon rearing investment and overall fish health. Longer term impacts will be felt by conservation programs, with the reduction in risks to threatened and endangered fish populations through better disease control. Finally, managers of a variety of global aquatic systems, like those concerned with recent fish virus disease outbreaks in the US Great Lakes and the international Atlantic salmon industry, will benefit from what we learn about the drivers of aquatic pathogen emergence.
Animal Health Component
Research Effort Categories
Goals / Objectives
We propose to develop informative models of transmission dynamics for infectious hematopoietic necrosis (IHN) virus, a globally important pathogen of salmon and trout. This study will focus on documented viral emergence and displacement events that have occurred in Pacific Northwest river systems by testing IHN viral genotypes associated with these events in relevant fish host populations that vary in IHN virus susceptibility. Aim 1 will quantify the relative importance of spatially- and temporally-associated variables in IHN viral epidemic events and genotype divergence in Pacific Northwest river systems. Aim 2 will define viral factors associated with transmission and fitness of four IHN viral variants involved in emergence and displacement events in the field. Aim 3 will quantify the interaction between genetic and environmental factors that affect host susceptibility to viral disease and emergence. Aim4 will integrate experimental and field data in a Bayesian hierarchical model to generate inference about viral transmission, prediction of emergence, and testing of virus control strategies. We will rapidly disseminate the result of our interdisciplinary research through established ties with specific groups that can utilize the data to inform policy decisions about fish resource management. Dissemination of results will be achieved by direct interaction with these groups, and by continued updating of our existing online database of IHN virus genetic typing. A new synthetic database will also be a product of Aim 1 and will also be provided freely online on the Western Fisheries Research Center (U.S. Geological Survey) website. As part of our outreach plan we will develop a curriculum entitled Fundamental Drivers of Aquatic Pathogen Transmission that will be offered at the end of the project as a continuing education course at the annual AFS Fish Health meeting, and as an online version available through the Western Fisheries Research Center websites
In Aim 1, we will create a synthetic database that includes all available diagnostic and genetic typing data for field-collected infectious hematopoietic necrosis (IHN) virus samples and the associated measures of environmental and ecological conditions. This will be done by careful reconciliation of reports from various agencies and integration of geospatial data at varying scales. This database will allow us to evaluate ecological determinants of IHN viral transmission and interactions between environmental and/or population characteristics that may influence transmission and viral genotype emergence. In Aim 2, the goal is to define virulence, infectious dose and virus shedding of four IHN viral types under laboratory conditions. These four IHN virus types sequentially emerged in the steelhead trout in the Columbia River basis with each field emergence displacing the former type. This analysis will determine the statistical differences in virulence between types and how it correlates with viral displacement and emergence. We will assess the transmission potential of the four viral types in terms of the kinetics and quantity of virus shed from infected fish. Viral fitness in co-infection and super-infection for pairs of IHN viral types associated with field displacement events will also be evaluated. Finally, we will address the probabilities of long-term infection outcomes and determine the frequencies and duration of viral persistence compared to the frequency of viral clearance over a 1 year period. In Aim 3, the focus shifts to the interaction between genetic and environmental factors that affect host susceptibility to viral disease and emergence. We will compare the reactions of host populations that differ in IHNV susceptibility, under two different temperature regimes, to determine whether host susceptibility a stable trait when environmental conditions shift and if the kinetics of the immune response and infection dynamics differ depending on temperature. Markers associated with IHNV resistance will be identified using genome wide association studies and these markers will be evaluated in other steelhead populations. In Aim 4, we will integrate experimental and field data in a Bayesian hierarchical model to generate inference about viral transmission, prediction of emergence, and testing of control strategies. This will include defining landscape-level dynamics of IHNV and assessing the relative importance of different IHNV transmission routes. This will allow us to test hypotheses regarding IHNV persistence in populations, the influence of host susceptibility and environment on IHNV expansion, and how management actions influences IHNV transmission. Furthermore, we will address the hypothesis that areas where multiple viral types have emerged in the past will share predictive traits with future sites of emergence and displacement. Finally, the effects of management options for dealing with epidemics and their effects on potential emergence events will be evaluated within the model.