Host Response to PRRS Infection and Opportunities to Exploit Host Genetic Variation

Porcine reproductive and respiratory syndrome (PRRS) is the most economically important disease in pig populations worldwide. Research to date, both 'in-vitro' and 'in-vivo', has failed to provide industry with a reliable or effective method to combat this devastating viral disease. Epidemiological models have been applied to viral infections and have demonstrated that selection for resistance can impact on reducing the likelihood of epidemics. Such studies have identified that PRRS is a suitable target for genetic studies of host resistance to disease (Bishop and MacKenzie, 2003). Key components to any selection programs include characterising genetic variation andidentifying genetic markers or Quantitative Trait Loci (QTL)associated with any resistance to, or tolerance of, the pathogen. The first step in the identification of these markers is to quantify the traits of interest and highlight genetic variation. The work described here also serves as a proof of concept that 'in-vitro' pre-screening can be used to identify breeds differing in response to PRRS virus (PRRSV) infection - an earlier study showed that Landrace alveolar macrophages were more resistant/tolerant than other breeds to the H2 PRRSV infection (Ait-Ali et al., 2006). This objective of this study was to infect gilts with PRRSV and assess the phenotypic consequences of infection. In addition, this study supplied RNA for gene expression studies (reported elsewhere).