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ARS Home » Research » Research Project #431942

Research Project: Rift Valley Fever Pathogenesis, Epidemiology, and Control Measures

Location: Foreign Arthropod Borne Animal Disease Research

2020 Annual Report

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.

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
Rift Valley fever (RVF) virus (RVFV) is an exotic zoonotic pathogen that poses a significant arthropod-borne animal disease threat to U.S. livestock if introduced. Objective 1 focuses on identifying factors associated with infections, pathogenesis, and epidemiological maintenance in the arthropod vector and vertebrate animal hosts. Specifically, Objective 1A is directed toward identifying markers of viral molecular determinants of virulence and mechanisms of viral pathogenesis. An important aspect to RVFV evolution is that because the genome consists of three segments they can be exchanged between different genetic types and potentially very closely related viruses. The rate this can occur is important to know, especially when an attenuated live vaccine is the only conditionally approved vaccine in the U.S. Tools to evaluate RVF reassortment have been developed in fiscal year 2020. The rate of reassortment from two distinct virulent strains and the attenuate live vaccine and virulent strain have been accessed in sheep. The data analysis and compilation are in progress. In Objective 1B, the further evaluation of host responses to virus and/or mosquito (Culex tarsalis) saliva in primary bovine macrophage cells was conducted. This information is being used to better understand mosquito saliva enhancement of infection. The virus growth characteristics of both the attenuated vaccine strain and a virulent strain of RVFV in this primary cell-lines has been established. Work to quantitate the effects of the presence of a virus and/or mosquito saliva on specific immunological markers has been completed. The data analysis and compilation are in progress. Under Objective 2A we developed the means to detect and characterize emergent arboviral diseases and generate models to predict future outbreaks. Two assays to detect antibodies to RVFV developed in the previous project were further validated in the laboratory and the field. Additionally, new pathological tools were established to assess presence of RVF viral genome or proteins in tissues. Current studies are directed at rapid detection and characterization of arboviruses in the field. In Objective 2B, machine learning and Kalman filters (methods to differentiate the true signal from the noise in the data) were used to make predicative models for the abundance and distribution of a common disease vector, the Asian tiger mosquito (Aedes albopictus) based on environmental factors (temperature and precipitation). The entomological risk is estimated per month globally. Furthermore, the locations of mosquito collections and dengue cases are mapped as well. Experimental investigation of environmental factors, such as ambient temperature on RVFV transmission by Culex tarsalis (known U.S. vector of West Nile virus) and Aedes taeniorhynchus (known vector of encephalitic viruses) were conducted to increase accuracy risk models for viral persistence and spread in nature. The project also used the Invasive Mosquito Project (the USDA’s citizen science/community outreach program) partnered with the Centers for Disease Control (CDC) to recruit zoos to participate in long-term national surveillance of mosquitoes and pathogens. New insect mass traps developed with the USDA-ARS innovation funds were distributed to zoos who use CDC funds to collect and test the mosquitoes for pathogens. Furthermore, the USDA partnered with the National Science Foundation’s National Ecological Observation Network to collect biting flies in 20 distinct ecosystems throughout the United States. These partnered projects increase the number of long-term collection locations beyond citizen scientists.

1. Development of a test for antibodies to Rift Valley fever virus. ARS researchers in Manhattan, Kansas, along with collaborators at Kansas State University developed and evaluated a serological assay using antisera from sheep and cattle experimentally infected wildtype Rift Valley fever virus (RVFV) strains, and sera of indigenous sheep and goat populations exposed to natural RVFV field infection in Gambia. The high specificity and correlation with the virus neutralization test support the feasibility of using the recombinant RVFV Nucleocapsid protein (N)-based indirect enzyme-linked immunosorbent assay (ELISA) to assess RVF seroprevalence in livestock in endemic and non-endemic areas. This assay doesn’t require propagation of RVFV thus is a safe to produce serological assay for antibodies to the zoonotic RVFV.

2. Environmental temperature effect mosquito transmission of Rift Valley fever virus. ARS researchers in Manhattan, Kansas, and collaborators at U.S. Army Medical Research Institute for Infectious Diseases evaluated how environmental temperature affects the ability of mosquitoes to transmit numerous arboviruses including for Rift Valley fever virus (RVFV). The effect of incubation temperatures ranging from 14-26ºC on infection, dissemination, and transmission rates for Culex tarsalis and Aedes taeniorhynchus. The results indicated that increase dissemination and transmission due to temperature was species dependent. This data on the effects of environmental factors, such as ambient temperature, ensures accurate development models for viral persistence and spread in nature.

3. Demonstration of the immunogenicity of Schmallenberg virus (SBV) glycoproteins. ARS researchers in Manhattan, Kansas, and collaborators at Kansas State University developed a novel differentiating infection from vaccinated animals (DIVA)-compatible SBV vaccines using viral glycoproteins expressed in baculovirus and evaluate their immunogenicity and efficacy in cattle. Two separate trials in six-month old dairy cattle were conducted using two different formulations. Neither of the SBV candidate vaccines prevented viremia nor conferred protection against SBV infection. Hence, future studies should focus on better understanding the role of different SBV proteins in inducing sustainable, protective immunity against SBV infection in ruminants.

4. Mosquito transmission models used for COVID-19 modeling. ARS researchers in Manhattan, Kansas, and collaborators at Kansas State University developed robust mathematical models to forecast outbreaks of mosquito transmitted pathogens. By changing the epidemiological data in the models, these models were adapted to predict the coronavirus disease outbreak (COVID-19) in China. The short-term predictions accurately estimated the new daily cases 72 hours prior to reporting. Second, an individual-level network-based model reconstructed the epidemic dynamics in Hubei Province during the early stage and examined the effectiveness of non-pharmaceutical interventions such as social distancing and masks on the viral spread. The development of predictive models that can be applied to exotic and domestic viral pathogens will better position resources or to initiate mitigation strategies prior to case detection or epidemic peaks. These models allow U.S. agriculture and public health agencies to be responsive rather than reactive to disease outbreaks and specifically exotic mosquito transmitted pathogens such as Japanese encephalitis or Rift Valley fever if they were introduced to the United States.

Review Publications
Wilson, W.C., Kim, I., Trujillo, J., Sunwoo, S., Noronha, L.E., Urbaniak, K., Mcvey, D.S., Drolet, B.S., Morozov, I., Faburay, B., Schirtzinger, E.E., Koopman, T., Indran, S., Balaraman, V., Richt, J. 2018. Preliminary evaluation of the susceptibility of white-tailed deer (Odocoileus virginianus) to Rift Valley Fever Virus. Emerging Infectious Diseases. 24(9):1717-1719.
Endalew, A., Morozov, I., Davis, A.S., Gaudreault, N.N., Wernike, K., Bawa, B., Ruder, M.G., Drolet, B.S., McVey, D.S., Shivanna, V., Ma, W., Faburay, B., Wilson, W.C., Richt, J.A. 2018. Virological and serological responses of sheep and cattle to experimental Schmallenberg virus infection. Vector-Borne and Zoonotic Diseases. 18:697-703.
Ragan, I., Schuck, K.N., Upreti, D., Odendaal, L., Richt, J., Trujillo, J.D., Wilson, W.C., Davis, A.S. 2019. Rift valley fever viral RNA detection by in situ hybridization in formalin-fixed, paraffin-embedded tissues. Vector-Borne and Zoonotic Diseases. 19(7):553-555.
Ragan, I., Davis, S.A., McVey, D.S., Richt, J., Rowland, R.R., Wilson, W.C. 2018. Evaluation of fluorescence microsphere immunoassay for the detection of antibodies to Rift Valley Fever nucleocapsid protein and glycoproteins. Journal of Clinical Microbiology. 56(6):e01626-17.
Neng, J., Li, Y., Driscoll, A., Wilson, W.C., Johnson, P. 2018. Detection of multiple pathogens in serum using silica-encapsulated nanotags in a surface-enhanced Raman scattering-based immunoassay. Journal of Agricultural and Food Chemistry. 66:22:5707-5712.
Faburay, B., Wilson, W.C., Secka, A., Drolet, B.S., McVey, D.S., Richt, J. 2019. Evaluation of an indirect enzyme-linked immunosorbent assay based on recombinant Baculovirus-expressed Rift Valley Fever virus nucleoprotein as the diagnostic antigen. Journal of Clinical Microbiology. 57(10):e01058-19.
Faburay, B., Labeaud, A., McVey, D.S., Wilson, W.C., Richt, J. 2017. Current status of rift valley fever vaccine development. Popular Publication. 5(3):29.