Analysis of the Host Genetics Influence on PCV2 Susceptibility

Porcine circovirus 2 (PCV2) is the main source responsible for inducing a group of associated diseases known as Porcine Circovirus 2 Associated Diseases (PCVAD) that affects production efficiency and can lead to mortality. Crossbred pigs (n = 974) based on 13 lines and generated by seven breeding programs were experimentally infected with a PCV2b strain to evaluate variation in viral replication, immune response and growth during challenge. Genome-wide sources of the variation of the indicators of PCV2 susceptibility were analyzed based on a Bayes B model that included genotypes of 56,433 SNPs. Proportion of the phenotypic variation explained by SNP variants in weekly viremia varied from 19% (7 dpi) to 52% (14 dpi) and 64% for viral load. Two major SNPs that explain 11.5% (SSC12) and 2.8% (SSC7) respectively, of the genetic variation for viral load were uncovered. These SNPs partially explained the negative correlations between viral load and ADG during challenge (r = -0.36, P < 0.0001). Genetic dissection of these two regions suggested that polymorphic regions in the swine leukocyte antigen class II (SLAII) could be one of the sources of the observed effects. Sequencing targeted genes showed that SLAII profile of the resource population was rich in non-synonymous SNPs harbored in a diverse collection of haplotypes. Some of the novel genetic variants uncovered influence or are closely linked with variants that affect host potential to modulate immune response and consequently impact PCV2 replication and animal health.