Date Full Report Received08/02/2010
Date Abstract Report Received08/02/2010
InvestigationInstitution: University of Nebraska
Primary Investigator: Fernando Osorio
Co-Investigators: Asit Pattnaik
Funded ByNational Pork Board
Work in our laboratories is exclusively oriented towards the development of a new generation of PRRSV vaccines that would confer broad protection. We work, through different basic and applied projects and with the participation of different members of our laboratories, towards such main goal. This particular proposal has been aimed at developing an optimal marker differential vaccine system for the new generation of vaccines currently under development. The main hypothesis is that the optimal new generation PRRSV vaccine will be of the live-attenuated type. The live-attenuated PRRSV vaccines are more effective because their components or antigens that are determinants of protection are “seen” by the pig’s immune system in a similar way as are seen those of live wild-type (fully infectious) PRRSV. Our ultimate goal is to develop a live vaccine of high safety and efficacy that would be compatible with the ability of cleansing the PRRSV infection from a herd, that is, compatible with the ability of differentiating, through a simple test, the vaccinated/protected animals from those that have suffered infection by wild-type PRRSV. Engineering of new live-attenuated PRRSV marker vaccines requires knowledge of the genetic make-up of PRRS antigens and identifying small areas of the proteins which can be eliminated from the vaccine without affecting the virus’ ability to multiply in cells and in the pig. This concept is similar to that successfully applied for the development of Pseudorabies marker vaccines. The differential vaccines, which, like in the example of Pseudorabies, were originally called “marker vaccines” are now also identified as DIVA vaccines (which stands for “Differentiating Infected from Vaccinated Animals”). With previous support from swine producers (NPB 06-177), we had developed the first prototype of DIVA live vaccine for PRRSV through the elimination of small protein fragment (epitope) from the make-up of these vaccines. Such vaccine candidate, although falling short of being a perfect marker vaccine, served as proof of the concept and encouraged further research on more efficient small protein fragments that can be used as markers. We attempted such task through this most recent project now being reported (#08-248). The specific objectives of this proposal were: 1) To develop a live PPRSV mutant deprived of the 201 ORF6 epitope reactivity, a small part of the PRRSV M protein which our results would suggest to be the ideal marker, based on its level of conservancy among many PRRSV strains 2) Testing of this epitope 201-deprived mutant in vivo , using an standard experimental design for animal inoculation which has been previously tested and described. 3) Field testing of the companion peptide-ELISA specific for the marker epitope, validating its specificity and sensitivity based on the analysis of a large number of field serum samples. At the end of this NPB supported project we know much more about all these three points, and significant advances have been made, although a final product is not available yet. Thanks to the work conducted under this project, we have now a much better sense of the technical modifications and new constructs that are needed to be explored in order to secure a stable and effective prototype of live marker vaccine. This research is being continued in our laboratories beyond the termination of this project NPB #08-248. A major obstacle to overcome in the next series of experiments has to do with developing a stable live mutant of PRRSV that would not revert to the wild-type type PRRSV after injected in a pig. Such stability of the strain in vivo is essential to maintain the “marker negative” character of the DIVA vaccine strain. The specific points of this research are presented in more detail under the discussion section of this report.