Host-genetic-based outcome of co-infection by PCV2b and PRRSV in pigs

Replication of porcine circovirus type 2 (PCV2), an important worldwide swine pathogen, has been demonstrated to be influenced by host genotype. Specifically, a missense DNA polymorphism (SYNGR2 p.Arg63Cys) within the SYNGR2 gene was demonstrated to contribute to variation in PCV2b viral load and subsequent immune response following infection. PCV2 is known to induce immunosuppression leading to an increase in susceptibility to subsequent infections with other viral pathogens such as porcine reproductive and respiratory syndrome virus (PRRSV). In order to assess the role of SYNGR2 p.Arg63Cys in co-infections, pigs homozygous for the favorable SYNGR2 p.63Cys (N = 30) and unfavorable SYNGR2 p.63Arg (N = 29) alleles were infected with PCV2b followed a week later by a challenge with PRRSV. A lower PCV2b viremia (P < 0.001) and PCV2-specific IgM antibodies (P < 0.005) were observed in SYNGR2 p.63Cys compared to SYNGR2 p.63Arg genotypes. No significant differences in PRRSV viremia and specific IgG antibodies were observed between SYNGR2 genotypes. Lung histology score, an indicator of disease severity, was lower in the pigs with SYNGR2 p.63Cys genotypes (P < 0.05). Variation in the lung histology scores within SYNGR2 genotypes suggests that additional factors, environmental and/or genetic, could be involved in disease severity.