A multi-year research project on porcine reproductive and respiratory syndrome (PRRS) virus will collect data on large numbers of PRRS virus-infected pigs so that researchers can verify important genotypes and phenotypes that predict resistance, tolerance or susceptibility to PRRS virus infection.

A consortium of groups, including the National Pork Board, U.S. Department of Agriculture (USDA), universities, and private companies, have funded a first-of-its-kind approach to food animal infectious disease research. The goal of the PRRS Host Genetics Consortium (PHGC) is to assess the role of genetics in determining pig resistance and susceptibility to PRRS virus infection, pathology and growth effects.

Despite substantial research over the years, understanding what constitutes a protective immune response to PRRS virus remains elusive.

To unlock that mystery, research studies were designed to identify genetic alleles and chromosomal regions as well as blood proteins that might predict why some pigs clear PRRS virus while others remain persistently infected. Identification of these proteins could lead to the development of anti-PRRS virus biotherapeutics or vaccines.

The project uses a nursery pig model to assess resistance and susceptibility. Crossbred pigs from high-health farms were transported at weaning to biosecure Kansas State University facilities. Pigs were acclimated, then infected with PRRS virus and followed for 42 days post infection (dpi). Blood samples were collected at Days 0, 4, 7, 10, 14, 21, 28, 35 and 42 dpi. Weights were recorded weekly. DNA was prepared from every pig for genotyping.

Data is being recorded in the PHGC relational database at Iowa State University.

Results from the first four trials of 200 pigs per trial indicated that all pigs became PRRS virus-infected. Some pigs cleared virus from serum quicker than others; weight effects were variable and not correlated with virus levels.

These differences in virus/weight categories will enable genetic mapping studies, using whole genome association analyses of 60,000 single-nucleotide polymorphism (SNP) markers with the swine SNPchip, and serum and gene expression studies to compare data from pigs exhibiting resistance and maximum growth to PRRS-susceptible, reduced-growth pigs.

The USDA PRRS Coordinated Agricultural Project (PRRS CAP) and the federal swine genome program are supporting state-of-the-art genome and computer analyses to identify genetic determinants of resistance/susceptibility for the PRRS virus.

Researchers: Joan Lunney, USDA, Agricultural Research Service, Beltsville Animal Research Center; J.P. Steibel, Michigan State University; J. Reecy and M. Rothschild, Iowa State University; and M. Kerrigan, B. Trible and R. Rowland, all of Kansas State University. For more information, contact Lunney by phone (301) 504-9368, fax (301) 504-5306 or e-mail Joan.Lunney@ars.usda.gov.