2008 Annual Report 1a.Objectives (from AD-416) The objective of this project is to evaluate RVF Clone 13 vaccine viability as a possible U.S. veterinary vaccine and to assess the safety of the vaccine, and thus facilitate USDA, Center for Veterinary Biologics (CVB) to consider licensure in the U.S. 1b.Approach (from AD-416) ABADRL will perform and coordinated exploratory research centered on: i) insect vector susceptibility, competency and transmissibility of Clone 13 vaccine strain, ii) reversion to virulence potential of Clone 13 vaccine strain, iii) ability of Clone 13 vaccine strain to prevent virulent RVF virus replication in young animals, and iv) onset of immunity studies. 3.Progress Report The Department of Homeland Security (DHS) is supporting an extension of ABADRL’s RVF research efforts to conduct evaluation of the efficacy and safety of potential commercial veterinary vaccines and complementary diagnostics that are currently unavailable in the U.S. This has resulted in additional studies through the interagency agreements with the U.S. Army Medical Research Institute for Infectious Diseases (USAMRIID). These additional studies include vector competence studies for attenuated RVF vaccine candidates. Mosquito colonies that will facilitate this work have been or are being established at ABADRL. Preliminary studies have been conducted with wild-type RVFV to identify high priority mosquito species for this project. These studies also include application of new diagnostic test to a Differentiate Infected from Vaccinated Animal control strategy. ABADRL has obtained the necessary reagents to initiate this research through national and international collaborations. ABADRL has been investigating whether RVF Clone 13 could be considered a DIVA vaccine by performing Western blot analysis for the NSs protein deleted in Clone 13. Preliminary data suggests that sheep sera are immunoreactive against expressed NSs protein in Western blot analyses. This may provide a valuable assay to distinguish between naturally infected and vaccinated (Clone 13) animals against Rift Valley Fever. This finding is consistent with recent results reported by the Centers for Disease Control. Further investigation examining sera from vaccinated and uninfected animals will be necessary to confirm these findings.