Project Title: Sub-typing of PRRSV isolates by means of measurement of cross-neutralization reactions

Institution: University of Nebraska-Lincoln

Outcome/Results: A new typing system based on the immune response induced by a PRRS virus strain was investigated.

Summary: One of the major obstacles for PRRSV control is the significant variability of this virus in the field. Such variability of PRRSV is expressed as genetic information of the strains (commonly detected by PCR followed by gp5 sequencing) and also, and most importantly, in the protein make-up of the PRRSV strains. These proteins of the PRRS virus determines the strain’s ability to induce specific protective immunity in the pig. There is a significant need for typing and classifying PRRSV strains by some means different than the genetic sequencing now in use. Rather than genetic sequencing, a typing system based in the distinct ability of strains to induce similar or different immune responses is a way to classify and group the large universe of PRRSV strains circulating in the field. To our knowledge this project is the first attempt worldwide to apply such a typing system for PRRSV. We designed reference antisera under the assumption that the main PRRSV glycoprotein 5 of PRRSV plays a central role in antigenic diversity and neutralizing activity of PRRSV. With this concept in mind, we were unable to type 50 % of the samples analyzed. While the typing done so far is incomplete, the results obtained, when joined with sequencing studies currently ongoing under different collaborative projects with SDSU and ISU should shed light on the role of specific structural genes of PRRSV. Such information could then be used to increase the number of reference antisera to be incorporated in our library so to maximize the number of “typable” isolates. Likewise, a closer analysis of some strains with abnormal reactivity detected by this research should teach us about the possibility of occurrence of PRRSV strains originated by crossing of Euro X U.S. types that may be occurring in the field. This latter information is also crucial for PRRSV control, as there is ample evidence for the simultaneous circulation of both serotypes within the same geographic areas of the US.