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Research Project: Assessing the Risk of Emergence, Transmission and Establishment of the Japanese Encephalitis Virus in the United States

Location: Foreign Arthropod Borne Animal Disease Research

Project Number: 3022-32000-025-019-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Aug 1, 2023
End Date: Apr 1, 2028

Objective: Identify factors associated with Flavivirus infections, pathogenesis and maintenance in vectors and animal hosts to inform prevention and mitigation strategies. (A) Identify factors associated with JEV maintenance in relevant insect vectors. Update and re-assess the existing qualitative risk assessment to estimate the risk of emergence of JEV into the continental US, Alaska and Hawaii, and subsequent transmission by incorporating the latest scientific information and elements contributing to the risk, which may have been previously overlooked. This study will ultimately provide a framework necessary for decision-makers to assess the risk of JEV considering both likelihood of occurrence and potential impacts. Revisiting the pathways of introduction and considering paths, either inadvertent or intentional, that were previously deemed non-important or that were disregarded, can lead to different assumptions and therefore, different probability estimates and risk ratings. (B) Characterize susceptibility, pathogenesis, and clinical disease of JEV in swine. Conduct a systematic review of the literature appraising peer-reviewed literature on the role of pigs (domestic and feral) in the transmission of JEV. Specifically, aspects related to susceptibility, pathogenesis and clinical manifestations will be gathered from this study. A formal identification of data gaps, using previously validated tools, will be also pursued. (C) Characterize vector-host interactions associated with JEV transmission. Our prior systematic review evaluating vector and host competence of JEV (Oliveira et al., 2018), along with our current work updating the SR (compiling evidence from 2016 to 2022), aligns with this sub-objective. We aim to identify whether new species of mosquitoes, new information on vectoral or host capacity, and new host species have emerged in recent years. Moreover, a deterministic compartmental model of JEV transmission in pigs will be built considering bird, pigs, feral pigs and mosquito vectors. When reevaluating transmission dynamics, parameters pertaining to host density, vector abundance, biting rate (interaction between host and vector), and the probability of transmission per bite will be revisited. The basic reproduction number will be computed, considering transmission from host to vector to host, vector to vector and from host to host (vector-free transmission), and upon further integrating climatic and regional factors, under specific local conditions. Similarly, we propose to construct, test and deliver a JEV spatial interaction model to estimate, predict, and forecast how a JEV outbreak in the US may spatiotemporally spread, and how a JEV outbreak can be controlled.

Various methods will be used to synthesize the scientific literature. (1) Rapid review: This will collect and appraise the available scientific evidence in a timely-manner following the Cochrane Rapid Reviews Methods Group. (2) Risk assessment: A qualitative assessment of the estimated the risk of emergence of JEV in the US will follow the framework for risk assessment of emerging vector-borne livestock diseases, which consists of a structured questionnaire. These data will then be imported into a semi-quantitative risk assessment model to quantify the risk posed by all potential pathways of JEV introduction in the US. (3a) Spatial interaction models: In collaboration with the Center for Ecology of Infectious Diseases (CEID) at the University of Georgia, a Japanese encephalitis virus (JEV) spatial interaction model will be constructed, evaluated, and delivered to estimate, predict, and forecast how a JEV outbreak in the United States may spatiotemporally spread, and how a JEV outbreak can be controlled. Researchers will leverage experience and existing code base to model the potential spread of JEV in the United States. A major hurdle is that spatial interaction models are customarily fit to data during on ongoing event. The transferability of models from one region to another or from one species to another has not previously been demonstrated. Nonetheless, considerable progress can be made by combining insights from models of JEV spatial spread in Australia and West Nile virus (WNV) spread in North America. Additionally, relevant covariate data (e.g., distribution of JEV competent Culex species, distribution of wild pigs, the spatial ranges of Ardeid birds, climatic conditions such as precipitation and temperature, and natural barriers such as the Rocky Mountains) could be incorporated into a model. Such a model could then be updated in real time during any future outbreak of JEV in the US. (3b) Modeling the 2022 Australian JEV Outbreak: The CEID proposes to form collaborative relationships with researchers in Australia to collect and catalog pertinent JEV data. If data can be obtained with sufficient time resolution, a spatial interaction model could then be used to estimate the effects of spatial covariates on spread rate. (3c) West Nile virus model: WNV is now found throughout the contiguous United States and similar to JEV. WNV is spatially spread by infected birds and Culex. County level records of the first reports of WNV can be used to fit a spatial interaction model for WNV spread in North America. (3d) Model for the potential spread of JEV in the United States. The WNV model will be compared with the Australia-JEV model to identify points of agreement and disagreement, e.g., effect of water bodies, estimated dispersal distances, etc. The WNV model will then be modified to account for the presence of wild pigs as a persistent wildlife reservoir and role of Ardeid birds in the long-distance movement of the virus.