Quantitative Trait Locus on Sus scrofa Chromosome 4 Associated with Host Response to Experimental Infection with Porcine Reproductive and Respiratory Syndrome Virus

The objective of this study was to conduct a genomewide association study to discover the genetic basis of host response to PRRS virus using data from the PRRS Host Genetics Consortium NPB and PRRS-CAP project. Approximately 1,600 commercial crossbred piglets were experimentally infected with the Porcine Reproductive and Respiratory Syndrome (PRRS) virus. Blood samples and body weights were collected up to 42 days post infection (dpi). Experimental pigs and their parents were genotyped with Illumina’s Porcine 60k BeadChip. Phenotypes analyzed were viral load (VL = area under the curve for log-transformed qRT-PCR based serum virus from 0-21 dpi) and weight gain from 0-42 dpi (WG). Heritabilities estimated using pedigree information were moderate at 0.41 for VL and 0.29 for WG. A 1 Mb region on Sus scrofa chromosome (SSC) 4 was found to be associated with VL and WG and explained a substantial amount of genetic variation. The frequency of the favorable allele for the most significant single nucleotide polymorphism (SNP) was 0.15. These results show that there is a host genetic component to PRRS virus infection and that there is room for genetic improvement

A Comparison of the Genetic Factors Influencing Host Response to Infection with One of Two Isolates of Porcine Reproductive and Respiratory Syndrome Virus

Host genetic differences in viral load (VL) and weight gain (WG) during porcine reproductive and respiratory syndrome virus (PRRSV) challenge were assessed for thirteen trials of ~200 commercial crossbred piglets each, from several different commercial suppliers. Piglets were experimentally infected with PRRSV isolates NVSL-97-7895 (NVSL) or KS-2006-72109 (KS06). VL and WG were moderately heritable and were antagonistically related for both virus isolates. The genetic correlation of host response to NVSL with host response to KS06 was high for both VL and WG. Consistent with previous findings, animals that were heterozygous (AB) for the WUR10000125 (WUR) marker on Chromosome 4 (SSC4) had significantly lower VL than their AA counterparts when infected with either virus isolate; however, a significant increase in WG was only observed when piglets were infected with the NVSL isolate. These results suggest that selecting for increased resistance or reduced susceptibility to PRRSV may be effective across virus isolates. Selecting for the AB genotype for WUR is expected to reduce VL across PRRSV isolates but its effect on WG during infection may differ between virus isolates

Genetic Parameters and Effect of WUR Genotype on Piglet Response to Co-Infection with PRRS and PCV2b, with or without Vaccination for PRRS

Commercial crossbred nursery piglets were either vaccinated or not using a modified live porcine reproductive and respiratory syndrome (PRRS) virus vaccine and all pigs were co-infected with PRRS virus (PRRSV) and porcine circovirus type 2b (PCV2b) 28 days later. Genetic correlations indicate that traits associated with primary exposure to PRRSV infection (PRRS viral load (VL) of vaccinated pigs prior to co-infection and PRRS VL of non-vaccinated pigs post co-infection) are genetically the same trait. The WUR single nucleotide polymorphism on chromosome 4, previously associated with reduced PRRS VL under PRRSV-only infection, was associated with significantly reduced PRRS VL following vaccination and co-infection (for non-vaccinated pigs), but also with reduced PCV2b VL of vaccinated pigs. These results indicate a significant effect of WUR genotype on PRRS VL upon primary PRRS exposure, whether in a PRRSV-only or PRRS and PCV2b co-infected population, but also with PCV2b VL of vaccinated pigs under PRRS and PCV2b co- infection

Factors Associated with N-specific IgG Response in Piglets Experimentally Infected with Porcine Reproductive and Respiratory Syndrome Virus

This study examined serum porcine reproductive and respiratory syndrome virus (PRRSV) N protein-specific IgG levels from sera collected from 464 Large White-Landrace commercial crossbred piglets from three separate experimental infection trials with PRRSV isolate NVSL-97- 7895. IgG levels at 42 days post infection (dpi) were measured by fluorescent microsphere immunoassay, herein referred to as total antibody (tAb) response. tAb levels were assessed for an association with different disease-related traits, the presence of a heritable genetic component, and for genomic regions associated with tAb response. tAb response was negatively associated with viral load (VL) and weight gain from 28-42 dpi (WG) and positively associated with virus rebound (REB) and neutralizing antibody (nAb) levels. Furthermore, tAb response had a heritable genetic component, with a major QTL located on chromosome 7 in the major histocompatibility complex (MHC), whereby heterozygous individuals had a lower tAb response and increased weight gain from 28-42 dpi. These results suggest that genetic selection for tAb response may be useful for selecting for pigs that have increased resistance or reduced susceptibility to PRRSV

Validation of the Effects of a SNP on SSC4 Associated with Viral Load and Weight Gain in Piglets Experimentally Infected with a 2006 PRRS Virus Isolate

Host genetic differences in viral load (VL) and weight gain (WG) during challenge were assessed for five trials of ~200 commercial crossbred piglets each, all from different commercial suppliers. Piglets were experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV) isolate KS-2006-72109 in order to validate the effects of a SNP previously identified on SSC4 (WUR10000125), whereby AB individuals had increased WG and reduced VL when experimentally infected with PRRSV isolate NVSL-97-7895. VL was defined as the area under the curve of logged viremia from 0-21 dpi. WG was defined as the weight gained from 0-42 dpi. The SNP effects on VL and WG were assessed. AB individuals had higher WG and lower VL than AA individuals, suggesting this marker may be useful for genetic selection of pigs for increased resistance or reduced susceptibility to PRRSV isolates that differ genetically and possibly pathogenically

Pigs Selected for Increased Feed Efficiency Are Less Affected by Experimental Infection with the PRRS Virus

Analyses of average daily gain (ADG) and viral load (VL) suggest that selection for increased feed efficiency based on residual feed intake (RFI) does not increase the impact of Porcine Reproductive and Respiratory Syndrome (PRRS) infection on these two traits. In fact, the results show that growth of the more efficient pigs was less affected by PRRS infection than that of the inefficient line. These findings provide commercial farmers with additional incentives to invest in feed-efficient pigs

Effect of WUR Genotype and PRRS Vaccination on Pigs Co-Infected with PRRS and PCV2b

Average daily gain (ADG) and viral load (VL) were evaluated for pigs co-infected with porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) and porcine circovirus type 2b (PCV2b). Pigs were pre-selected for WUR genotype (a marker on chromosome 4 associated with weight gain and VL under PRRSV-challenge), half were vaccinated for PRRS, and half were not. Results indicate that vaccination for PRRS resulted in slower growth prior to co-infection and that the AB WUR genotype was associated with faster growth prior to co-infection, lower PRRS VL, and lower PCV2b VL in vaccinated pigs

The Effect of PRRS Viral Level and Isolate on Tonsil Gene Expression

Porcine Reproductive and Respiratory Syndrome virus (PRRSV) can persist in tonsil tissue for \u3e150 days post infection (dpi) without clinical signs.This can occur even when PRRSV is cleared from serumand can result insecondary outbreaks. Tonsil tissue from commercial crossbred pigs that were experimentally infected with one of two PRRSV isolates, NVSL-97-7985 (NVSL) or KS-2006-72109 (KS06),was used to identify genes that were differentially expressed in pigs with extreme high or low tonsil PRRS viremia at 42 dpi. Results provide insighton the mechanisms of PRRSV persistence in tonsils and help to identify bio-markers for PRRSV persistence in tonsil tissue.This maylead tothe development of more effective strategies to reduce the chance of PRRS re-breaks

Genetic Parameters and Chromosomal Regions Associated with Viral Load and Growth in Pigs Infected with Porcine Reproductive and Respiratory Syndrome Virus

Six hundred commercial crossbred piglets were experimentally infected with the Porcine Reproductive and Respiratory Syndrome (PRRS) virus. Blood samples and body weights were collected at least once per week throughout the 6-week test period. Blood samples were used to measure the degree of infection through viral load. Body weight was measured to look at the impact of the PRRS virus on growth. Serum viral load from day 0 to 21 were summarized by area under the curve. Heritability for viral load and weight gain from 0 to 42 days after infection was 0.28 and 0.26, respectively. All piglets were genotyped for over 60,000 genetic markers comprising single nucleotide polymorphisms (SNPs) distributed across the genome. Regions on chromosomes 3, 4, and X appeared to be associated with area under the curve, while regions on chromosomes 1, 4, 7, and 17 appeared to be associated with weight gain. These results are promising to the swine industry, as it shows that there is genetic variation for resistance to PRRS within a population and that selection for resistance or susceptibility to the virus is plausible