Effect of a major quantitative trait locus for porcine reproductive and respiratory syndrome (PRRS) resistance on response to coinfection with PRRS virus and porcine circovirus type 2b (PCV2b) in commercial pigs, with or without prior vaccination for PRRS1

Abstract

A major QTL for host response to porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) infection was identified in a previous study. Single nucleotide polymorphism WUR10000125 (WUR), which is in complete linkage disequilibrium with the putative causative mutation, can be used as a tag SNP for the QTL. However, the effect of WUR following PRRS vaccination and/or coinfection with other pathogens is not known. Therefore, objectives of this study were to estimate the effect of WUR on host response following PRRS vaccination and coinfection of PRRSV with porcine circovirus type 2b (PCV2b), to estimate genetic parameters for host response to vaccination and coinfection, and to estimate the effect of previously identified candidate SNP under PRRSV-only or PCV2b-only infection on host response to coinfection. Data from 2 trials, comprising a total of 396 commercial crossbred nursery pigs from a single genetic source, were used for all analyses. Pigs were preselected based on WUR genotype: approximately half AA and half AB, where B is the favorable and dominant allele. At weaning, pigs were shipped to Kansas State University, where half of the pigs were vaccinated with a PRRS modified live virus vaccine. Four weeks later, all pigs were coinfected with field strains of PRRSV and PCV2b and followed for 42 d. Body weight and serum viremia measurements were collected following vaccination and coinfection to calculate ADG and viral load (VL), respectively. Average heritability estimates for PRRS VL, PCV2b VL, and ADG were 0.29, 0.09, and 0.40, respectively. After vaccination, AB pigs had lower vaccination VL ( = 0.03) and faster gain ( = 0.004) than AA pigs, as expected. After coinfection, AB pigs had lower PRRSV VL ( < 0.001) but did not significantly differ from AA pigs in growth rate ( = 0.86). For PCV2b VL, suggestive evidence of an interaction between vaccination and WUR genotype ( = 0.11) was detected, where AB pigs had significantly lower PCV2b VL when vaccinated ( = 0.007) but not when they were not vaccinated ( = 0.87). In addition to WUR, several PRRS-associated SNP and a PCV2b-associated SNP had significant effects on host response to coinfection. In conclusion, marker-assisted selection based on WUR genotype alone, or along with other candidate SNP for PRRSV and PCV2b infection, is a promising strategy to select for improved host response to not just PRRS but also coinfection of PRRSV with PCV2b and perhaps other pathogens.

Genomic regions associated with host response to porcine reproductive and respiratory syndrome vaccination and co-infection in nursery pigs

“…Results from Dunkelberger et al [ 7 ] showed that WUR had a significant effect on vaccination VL as well as PRRS VL and PCV2b VL of Vx pigs, but not PCV2b VL of Non-Vx pigs. Results also showed that, numerically, the effect of WUR on PRRS VL was greater following primary versus secondary PRRSV exposure, which is consistent with the biological role of GBP5 .…”

“…A detailed description of the animals used for this study is in Dunkelberger et al [ 7 ]. Briefly, commercial Large White x Landrace crossbred barrows from two experimental co-infection trials (trial 1 n = 199; trial 2 n = 197) were used.…”

“…A detailed description of the traits analyzed for this study, including descriptive statistics for all traits analyzed, is in Dunkelberger et al [ 7 ]. Briefly, 89 Non-Vx AA, 106 Non-Vx AB, 95 Vx AA, and 106 Vx AB pigs were used for all analyses.…”

“…To identify the effect of vaccination on the effect of genomic regions for host response to co-infection, bivariate animal models were used to analyze ADG Post Vx, PRRS VL, PCV2b VL, and ADG Post Co-X of Vx versus Non-Vx groups as two separate traits, as described in Dunkelberger et al [ 7 ]. For each bivariate GWAS, the following model was used to test the effect of each SNP averaged across vaccination status ( main effect ) and the interaction of SNP genotype with vaccination status ( interaction effect ):…”

“…Since the identification of this quantitative trait locus ( QTL ), the effect of WUR has been associated with host response to PRRS virus ( PRRSV )-infection following infection with two different PRRSV isolates [ 3 – 6 ], PRRS vaccination [ 7 ], and co-infection with PRRSV and porcine circovirus type 2b ( PCV2b ) [ 7 ]. In addition, WUR was associated with PCV2b viral load ( VL ) following PRRSV/PCV2b co-infection for pigs previously vaccinated for PRRS, but not for non-vaccinated pigs [ 7 ]. Other genomic regions, including regions on SSC7 and SSC12 have been associated with PCV2b VL following experimental infection with PCV2b only [ 8 ].…”