Location: Foreign Arthropod Borne Animal Disease Research
2017 Annual Report
Objectives
1. Identify factors associated with Bunyaviridae (Rift Valley Fever virus) infections, pathogenesis, and maintenance in arthropod vector and vertebrate animal hosts, including identifying viral molecular determinants of virulence and mechanisms of viral pathogenesis in relevant animal hosts associated with arthropod-transmitted virus, and characterizing host, vector and bunyavirus interactions (molecular and cellular) associated with virus infection.
Sub-objective 1A: Create a network based stochastic model that accounts for
mosquitoes, cattle and humans to determine the best mitigation strategies in the
event of an outbreak.
Sub-objective 1B: Develop tools for rapid detection and characterization of emergent viruses.
2. Identify epidemiological and ecological factors affecting the inter-epidemic cycle and disease emergence caused by Bunyaviridae (Rift Valley Fever virus), including developing means to detect and characterize emergent arboviral diseases and use these data to generate models that predict future outbreaks, and developing epidemiological models to identify biotic and abiotic factors that contribute to virus establishment, evolution, inter-epidemic maintenance, transmission and disease emergence.
Sub-objective 2A: Develop RVFV “vector-transmitted” infectious models in target
ruminant species to facilitate studies of disease pathogenesis, disease transmission and vaccine efficacy.
Sub-objective 2B: Identify mammalian host innate and adaptive responses to insect transmitted RVFV.
Approach
The potential introduction of Rift Valley fever (RVF) virus (RVFV) is the most
significant arthropod-borne animal disease threat to U.S. livestock according to the USDA-APHIS National Veterinary Stockpile (NVS) Steering Committee. A number of challenges exist for the control and prevention of RVF in the areas of disease
surveillance, diagnostics, vaccines and vector control. RVFV is the third biological threat agent on the NVS Steering Committee’s priority list for generation and stockpiling of countermeasures for diagnosis, vaccination, and insect control. Understanding the epidemiological factors affecting disease outbreak and the interepizootic maintenance of RVFV is necessary for the development of appropriate countermeasures strategies. This includes the ability to detect and characterize emergent viruses since RVFV is an RNA virus and could evolve to adapt to a new environment. Also, the proposed research will identify determinants of RVFV infection, pathogenesis and maintenance in mammalian and insect vector hosts. Information derived from these studies will also provide a better vaccine evaluation challenge model. Vaccine formulations will be developed to improve immunogenicity, onset of immunity and stability to provide better response to outbreaks and prevent RVFV epizootics. The overall goals of this project are to utilize the unit’s unique multidisciplinary expertise to fill knowledge gaps about the interepidemic cycle of RVFV and provide the tools necessary for detecting, controlling and eradicating RVFV should it be introduced into the U.S.
Progress Report
This project was initiated in late FY17 as a replacement for the 3020-32000-005-00D project. Please refer to the 3020-32000-005-00D report for further information on work completed in FY17.
Sub-objective 1.1.A. The Rift Valley fever virus (RVFV) reverse genetic system has been established in the laboratory and synthetic viruses representing two wildtype RVFV strains have been rescued (i.e. viable virus recovered). The pathogenicity in sheep of one of these synthetic strains has been compared to the wildtype strain has been performed, however the sample analysis is ongoing.
Sub-objective 1.1.B. Animal models to better evaluate vaccine control approaches have been developed that demonstrate virus produced in mosquito cells provided more consistent host response to infection. Experimental infections of young lambs and calves using two virulent strains of RVFV have been conducted. A preliminary vaccine challenge study with and ABADRU/Kansas State University subunit vaccine candidate has been conducted with a promising outcome. This vaccine is now in commercial development.
Sub-objective 1.1.B. The first experimental Rift Valley Fever Virus infection of livestock animal studies were conducted in previous project demonstrated strain differences in clinical pathology in an experimental model. Preliminary sequence analysis has indicated that quasispecies that is genetic variation amongst the population of viruses within an inoculum contributes to the pathological outcome of infection. This analysis is ongoing.
Sub-objective 1.1.B. To further evaluate insect vector-host-virus interactions and to improve RVFV challenge models, a Culex tarsalis colony was established and is being used to understand mosquito saliva enhancement of infection by evaluating the host responses to virus and/or mosquito saliva in primary bovine macrophage cells. This has recently been expanded to include ovine macrophage cells. The virus growth characteristics in this primary cell-lines has been established. This work is ongoing but immunological markers effected by presence of virus and/or mosquito saliva have been identified.
Sub-objective 2.2.A. The multiplex pathogen detection and characterization continues to be evaluated including the Fluorescence Microsphere Immunoassay and MassTag multiple pathogen detection systems. A patent application for the MassTag system has been submitted. Experimental lots of recombinant RVFV Np and NSs proteins were produced for use in further development of enzyme linked immunoassays (ELISA). The assay development has been extended to lateral flow assays for both laboratory confirmatory testing as well as rapid, presumptive field diagnostics. One ELISA is in commercial development and the evaluation locally and through international collaborations is being compiled.
Accomplishments
1. Development of a subunit vaccine for Rift Valley fever (RVF). RVFV is an important animal and human mosquito-transmitted pathogen in Africa that could be introduced into the United States. ARS researchers and collaborators at Kansas State University in Manhattan, Kansas developed an efficacious, safe to produce and use sub-unit RVFV vaccine for livestock. This candidate vaccine has been approved for patenting pending final documentation and was licensed for commercial company for development (APHIS license pending). The subunit vaccine provides a new tool to prevent RVFV disease outbreaks that is compatible with a differentiate infected from vaccinated animals approach using new diagnostic tools also developed by this team.
Review Publications
Hossain, M.M., Wilson, W.C., Faburay, B., Richt, J.A., McVey, D.S., Rowland, R.R. 2016. Multiplex detection of IgG and IgM to Rift Valley fever virus nucleoprotein, nonstructural proteins, and glycoprotein in ovine and bovine. Vector-Borne and Zoonotic Diseases. 16(8):550-557. doi:10.1089/vbz.2014.1721.
Hossain, M.M., Wilson, W.C., Rowland, R.R. 2017. Incorporation of antigens from whole cell lysates and purified virions from MP12 into fluorescence microsphere immunoassays for the detection of antibodies against Rift Valley fever virus. Virology Journal. 1:24-31.
Faburay, B., Wilson, W.C., Gaudreault, N.N., Davis, A., Shivanna, V., Bawa, B., Sunwoo, S., Ma, W., Drolet, B.S., Morozov, I., McVey, D.S., Richt, J.A. 2016. A recombinant Rift Valley fever virus glycoprotein subunit vaccine confers full protection against Rift Valley fever challenge in sheep. Scientific Reports. 6(27719):1-12. doi:10.1038/srep27719.
Wilson, W.C., Davis, A., Gaudreault, N.N., Faburay, B., Trujillo, J.D., Shivanna, V., Sunwoo, S., Balogh, A., Endalew, A., Ma, W., Drolet, B.S., Ruder, M.G., Morozov, I., McVey, D.S., Richt, J.A. 2016. Experimental infection of calves by two genetically-distinct strains of rift valley fever virus. Viruses. 8(145):1-16. doi:10.3390/v8050145.
