VIRUS-VECTOR-HOST INTERACTIONS OF ARBOVIRAL DISEASES OF LIVESTOCK
Location: Arthropod-Borne Animal Diseases Research
Title: Rift Valley Fever: International Coordinated Efforts from Early Warning to Rapid Responses
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 12, 2009
Publication Date: August 1, 2010
Citation: Wilson, W.C., Bennett, K.E., Mecham, J.O., Miller, M.M., Drolet, B.S. 2010. Rift Valley Fever: International Coordinated Efforts from Early Warning to Rapid Responses. Meeting Abstract. 301-303.
Scientists at the USDA, ARS, Arthropod-Borne Animal Diseases Research Laboratory (ABADRL) initiated research to develop operator-safe, rapid diagnostic tests and develop large animal models for both virulent and vaccine strains of Rift Valley Fever (RVF). The ABADRL currently does not have biological containment facilities that could be certified for virulent RVF research. Therefore, to accomplish this research mission, the ABADRL has relied on molecular applications and has established national and international cooperative agreements. The ABADRL and the Canadian Food Inspection Agency (CFIA) have been working together to develop clinical diagnostic test samples and a large animal infection model for vaccine evaluation. To date, six experimental virulent RVF infection studies with calves (four) and sheep (two) have been conducted at the CFIA laboratory. In addition, in the ABADRL BSL-2 facilities, three RVF MP-12 vaccine studies have been conducted in sheep. These studies have provided samples and reagents for ARS scientists and collaborators to develop of operator-safe BSL-2 diagnostics tools. One of these tools is a multiplex real-time RT-PCR that detects all three segments of RVF viral RNA and can distinguish between wild-type and several candidate attenuated vaccine strains. This assay was field tested at the Kenya Agriculture Research Institute and Kenya Department of Veterinary Services. The results indicated that some modifications were required, but overall the assay performed well, did not cross-react with Nairobi sheep disease virus and was more sensitive than existing nucleic acid detection assays. Immunological assays based on expressed glycoprotein (Gn), nucleocapsid (N) and Nonstructural protein (NSs) have also been developed and laboratory evaluated. International cooperative agreements are in place to allow for field evaluation of these diagnostic tests and of candidate RVF vaccines. The FAO/IAEA Animal Health and Production division has a coordinated research project of RVF veterinary surveillance in which ABADRL scientists participate as consultants. These interactions, along with the assistance of USDA, APHIS, will allow the development of internationally harmonized diagnostic tools for RVF in North America.
The ABADRL is also developing a RVF vaccine discovery project. In order to better evaluate RVF vaccine candidates, the ABADRL has been evaluating various tools to assess the humoral and cell-mediated immunity responses of sheep. The ABADRL, in collaboration with the U.S. Army Medical Research Institute for Infectious Diseases and CFIA, are evaluating the vector competence of North American mosquito species for infection and transmission of RVF virus. The West Nile virus vector, Culex tarsalis has been shown to be a competent vector for RVF. In addition, the origin of populations of Aedes vexans has been shown to affect this species vector competence. Thus, to effectively control the spread of RVF, knowledge of competence of geographic populations of vector species is needed. The ABADRL is working with ARS scientists at the Center for Medical, Agricultural, and Veterinary Entomology (CMAVE) have developed a Risk Assessment Model for RVF outbreaks in East Africa. ABADRL and CMAVE are coordinating insect vector research to further improve this model and develop vector control strategies. ABADRL, CMAVE, DHS, APHIS, CDC and various universities are coordinating research activities in a “One Heath” approach through a voluntary Interagency RVF working group, which was established to facilitate and coordinate U.S. research efforts. In summary, RVF is of significant concern in Africa and poses a significant threat to the US due to importations and globalization. The goal of these internal and international collaborations is to develop systems for early warning, early detection and more rapid and effective responses to this devastating disease. International cooperation is both mutually beneficial, and essential, in order to adequately evaluate the veterinary RVF countermeasure tools. ARS believes one of the most effective US countermeasures for the potential introduction of RVF is to provide tools to control the disease at its source.