Genetic relationships of antibody response, viremia level and weight gain in pigs experimentally infected with porcine reproductive and respiratory syndrome virus

Authors: HESS, ANDREW - Iowa State University; TRIBLE, BEN - Kansas State University; HESS, MELANIE - Iowa State University; ROWLAND, RRR - Kansas State University; Lunney, Joan; PLASTOW, G - University Of Alberta; DEKKERS, JCM - Iowa State University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2018
Publication Date: 6/20/2018
Citation: Hess, A.S., Trible, B., Hess, M.K., Rowland, R., Lunney, J.K., Plastow, G., Dekkers, J. 2018. Genetic relationships of antibody response, viremia level and weight gain in pigs experimentally infected with porcine reproductive and respiratory syndrome virus. Journal of Animal Science. 96:3565-3581. https://doi.org/10.1093/jas/sky229.
DOI: https://doi.org/10.1093/jas/sky229

Interpretive Summary: Our goal is to develop new markers for to identify pigs with improved responses to Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection and vaccination. This paper verifies that the level of serum anti-PRRSV antibody response at 42 days post infection is a trait that is heritable and may correlate with decreased viral loads and improved weight gain. Genome-wide association studies identified 3 markers on swine chromosome 7 in the Major Histocompatibility Complex are associated with antibody response level. These findings suggest antibody response to PRRSV infection is a possible biomarker for selection of pigs with increased resistance to PRRSV infection.

Technical Abstract: Genetic and antigenic variability between Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) isolates has encumbered the development of effective vaccines. Therefore, the potential of genetic selection on PRRSV antibody response to improve resistance to PRRSV infection was assessed using data from experimental trials in which commercial crossbred weaner pigs across eight trials were infected with one of two genetically distinct PRRSV isolates, NVSL-97-7895 (~750 pigs) and KS-2006-72109 (~450 pigs). The objectives here were to estimate the genetic parameters of antibody response, measured as the sample to positive ratio (S:P) of PRRSV N-protein specific IgG in serum at 42 days post infection (dpi); assess the relationship of antibody response with serum viremia and growth under infection; and identify genomic regions associated with antibody response. The heritability of antibody response under PRRSV infection was estimated at 0.31±0.09 (NVSL) and 0.40±0.10 (KS06). Antibody response under infection with these distinct PRRSV isolates appeared to be under similar genetic control, with an estimated genetic correlation of 0.73±0.39. Estimates of genetic correlations of S:P were generally weak with viral load (NVSL: -0.20±0.18; KS06: -0.69±0.20), measured as area under the curve of log10 serum viremia from 0 to 21dpi, and with weight gain from 0 to 42 dpi (NVSL: -0.38±0.19; KS06: -0.08±0.25). However, genetic correlations of S:P at 42 dpi with daily serum viremia revealed dynamic relationships across the experimental period (from -0.45 to +0.56 for NVSL and from -0.80 to -0.22 for KS06) and with 3-day weight gain (from -0.48 to +0.21 for NVSL and from -0.20 to +0.78 for KS06). The WUR10000125 SNP on SSC4, previously identified to be associated with response to PRRSV infection, did not have a significant effect on antibody level (P>0.05). Genotype-specific genetic correlations of S:P with daily viremia or 3-day weight gain, however, suggested that the lower weight gain observed in pigs with the unfavorable AA WUR10000125 genotype may be due to their utilization of a more energetically costly host response compared to pigs with the favorable genotype. Genome-wide association studies identified 3 SNPs in the Major Histocompatibility Complex associated with antibody response that explained ~10% (NVSL) and 45% (KS06) of genetic variance for S:P but were not associated with viremia or weight gain. Collectively, these findings suggest antibody response to PRRSV infection is a possible biomarker for selection of pigs with increased resistance to PRRSV infection.