Project Title: Emerging European-like PRRSV in the U.S.: Implications for diagnostic and control strategies

Institution: South Dakota State University

Outcome/Results: Genetic, pathogenic, and immunological properties of representative Type 1 (European-like) PRRSv isolates were evaluated. In addition, a panel of serum samples was developed using Type 1 isolates to serve as reference or control materials for diagnostic laboratories and other researchers.

Porcine reproductive and respiratory syndrome (PRRS) virus exists as two major genotypes, designated as Type 1 (European-like) and Type 2 (North American-like). The role and significance of European-like Type 1 PRRS viruses, recently identified in U.S. swine herds, is poorly understood. It is clear that ignoring Type 1 viruses will lead to additional problems in the control of PRRS. The overall goal of this study was to evaluate the genetic, pathogenic and immunological properties of representative Type 1 isolates from the U.S. and to develop panels of well-characterized serum samples to serve as reference or control materials for diagnostic laboratories and other researchers.

Genetic analysis, including the sequencing of whole virus genomes, reveals some important insights into the pathogenesis, diagnosis and evolution of Type 1 PRRS viruses. Funding from this study has provided genomic information for a relatively large number of isolates. The results show that Type 1 viruses are undergoing a remarkable evolution. Type 1 viruses appeared in the U.S. as the result of a limited introduction of viruses, but have shown some remarkable diversification into distinct groups. Our results indicate that this group of PRRS viruses will continue to change genetically. The detection of recombination is especially important, since it indicates that pigs can be infected with multiple isolates. Recombination is a source of new diversity and rapid evolutionary change.
Animal challenge studies with four selected European-like Type 1 PRRS virus isolates demonstrated minimal to moderate clinical signs in nursery to grower-age pigs. Substantial animal to animal variation within each challenge group existed in antibody responses, duration of viremia and viral loads, as detected by semi-quantitative PCR. Minimal cross-neutralization with typical North American Type 2 PRRS virus isolates was noted.

A major goal of this project was to develop an extensive reference panel of well-characterized pig sera that can be used by diagnostic laboratories as quality control standards for the detection of Type 1 PRRS virus isolates or antibody responses. Samples from this panel will also be used for validation of new diagnostic assays and to ensure that new technologies, such as biosensors, can detect all PRRS virus isolates. These reference panels are already being used in other projects funded by the National Pork Board and others and will provide funding leverage for new proposals submitted to various granting agencies.