| 2017 |
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Waide, E H; Tuggle, C K; Serão, N V L; Schroyen, M; Hess, A; Rowland, R R R; Lunney, J K; Plastow, G; Dekkers, J C M;
Porcine reproductive and respiratory syndrome (PRRS) is a devastating disease in the swine industry. Identification of host genetic factors that enable selection for improved performance during PRRS virus (PRRSV) infection would reduce the impact of this disease on animal welfare and production efficiency. We conducted genomewide association study (GWAS) analyses of data from 13 trials of approximately 200 commercial crossbred nursery-age piglets that were experimentally infected with 1 of 2 type 2 isolates of PRRSV (NVSL 97-7985 [NVSL] and KS2006-72109 [KS06]). Phenotypes analyzed were viral load (VL) in blood during the first 21 d after infection (dpi) and weight gain (WG) from 0 to 42 dpi. We accounted for the previously identified QTL in the region on SSC4 in our models to increase power to identify additional regions. Many regions identified by single-SNP analyses were not identified using Bayes-B, but both analyses identified the same regions on SSC3 and SSC5 to be associated with VL in the KS06 trials and on SSC6 in the NVSL trials ( < 5 × 10); for WG, regions on SSC5 and SSC17 were associated in the NVSL trials ( < 3 × 10). No regions were identified with either method for WG in the KS06 trials. Except for the region on SSC4, which was associated with VL for both isolates (but only with WG for NVSL), identified regions did not overlap between the 2 PRRSV isolate data sets, despite high estimates of the genetic correlation between isolates for traits based on these data. We also identified genomic regions whose associations with VL or WG interacted with either PRRSV isolate or with genotype at the SSC4 QTL. Gene ontology (GO) annotation terms for genes located near moderately associated SNP ( < 0.003) were enriched for multiple immunologically (VL) and metabolism- (WG) related GO terms. The biological relevance of these regions suggests that, although it may increase the number of false positives, the use of single-SNP analyses and a relaxed threshold also increased the identification of true positives. In conclusion, although only the SSC4 QTL was associated with response to both PRRSV isolates, genes near associated SNP were enriched for the same GO terms across PRRSV isolates, suggesting that host responses to these 2 isolates are affected by the actions of many genes that function together in similar biological processes.
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Harding, John C S; Ladinig, Andrea; Novakovic, Predrag; Detmer, Susan E; Wilkinson, Jamie M; Yang, Tianfu; Lunney, Joan K; Plastow, Graham S;
A large challenge experiment using North American porcine reproductive and respiratory virus (PRRSV-2) provided new insights into the pathophysiology of reproductive PRRS. Deep phenotyping of dams and fetuses identified maternal and fetal predictors of PRRS severity and resilience. PRRSV infection resulted in dramatic decreases in all leukocyte subsets by 2days post inoculation. Apoptosis in the interface region was positively related to endometrial vasculitis, viral load in endometrium and fetal thymus, and odds of meconium staining. Viral load at the maternal-fetal interface was a strong predictor of viral load in fetal thymus and odds of fetal death. However, interferon-alpha suppression, a consequence of PRRSV infection, was protective against fetal death. Although the prevalence of fetal lesions was low, their presence in fetal organs and umbilical cord was strongly associated with fetal compromise. Fetal death and viral load clustered in litters suggesting inter-fetal transmission starting from a limited number of index fetuses. Factors associated with index fetal infection are unclear, but large fetuses appear at greater risk. Disease progression in fetuses was associated with an up-regulation of genes associated with inflammation, innate immunity, and cell death signaling, and down-regulation of genes associated with cell cycle and lymphocyte quality. A number of maternal transcriptomic responses were associated with PRRS resilience including higher basal gene expression correlated with platelet function, interferon and pro-inflammatory responses. Twenty-one genomic regions across 10 chromosomes were associated with important traits including fetal viral load, fetal death and viability suggesting that selection for reproductive PRRS resilience may be possible.
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Dunkelberger, J R; Serão, N V L; Niederwerder, M C; Kerrigan, M A; Lunney, J K; Rowland, R R R; Dekkers, J C M;
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.
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Dekkers, Jack; Rowland, Raymond R R; Lunney, Joan K; Plastow, Graham;
PRRS is the most costly disease in the US pig industry. While vaccination, biosecurity and eradication effort have had some success, the variability and infectiousness of PRRS virus strains have hampered the effectiveness of these measures. We propose the use of genetic selection of pigs as an additional and complementary effort. Several studies have shown that host response to PRRS infection has a sizeable genetic component and recent advances in genomics provide opportunities to capitalize on these genetic differences and improve our understanding of host response to PRRS. While work is also ongoing to understand the genetic basis of host response to reproductive PRRS, the focus of this review is on research conducted on host response to PRRS in the nursery and grow-finish phase as part of the PRRS Host Genetics Consortium. Using experimental infection of large numbers of commercial nursery pigs, combined with deep phenotyping and genomics, this research has identified a major gene that is associated with host response to PRRS. Further functional genomics work identified the GBP5 gene as harboring the putative causative mutation. GBP5 is associated with innate immune response. Subsequent work has validated the effect of this genomic region on host response to a second PRRSV strain and to PRRS vaccination and co-infection of nursery pigs with PRRSV and PCV2b. A genetic marker near GBP5 is available to the industry for use in selection. Genetic differences in host response beyond GBP5 appear to be highly polygenic, i.e. controlled by many genes across the genome, each with a small effect. Such effects can by capitalized on in a selection program using genomic prediction on large numbers of genetic markers across the genome. Additional work has also identified the genetic basis of antibody response to PRRS, which could lead to the use of vaccine response as an indicator trait to select for host response to PRRS. Other genomic analyses, including gene expression analyses, have identified genes and modules of genes that are associated with differences in host response to PRRS and can be used to further understand and utilize differences in host response. Together, these results demonstrate that genetic selection can be an additional and complementary tool to combat PRRS in the swine industry.
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Kommadath, Arun; Bao, Hua; Choi, Igseo; Reecy, James M; Koltes, James E; Fritz-Waters, Elyn; Eisley, Chris J; Grant, Jason R; Rowland, Robert R R; Tuggle, Christopher K; Dekkers, Jack C M; Lunney, Joan K; Guan, Le Luo; Stothard, Paul; Plastow, Graham S;
It has been shown that inter-individual variation in host response to porcine reproductive and respiratory syndrome (PRRS) has a heritable component, yet little is known about the underlying genetic architecture of gene expression in response to PRRS virus (PRRSV) infection. Here, we integrated genome-wide genotype, gene expression, viremia level, and weight gain data to identify genetic polymorphisms that are associated with variation in inter-individual gene expression and response to PRRSV infection in pigs. RNA-seq analysis of peripheral blood samples collected just prior to experimental challenge (day 0) and at 4, 7, 11 and 14 days post infection from 44 pigs revealed 6,430 differentially expressed genes at one or more time points post infection compared to the day 0 baseline. We mapped genetic polymorphisms that were associated with inter-individual differences in expression at each day and found evidence of cis-acting expression quantitative trait loci (cis-eQTL) for 869 expressed genes (qval < 0.05). Associations between cis-eQTL markers and host response phenotypes using 383 pigs suggest that host genotype-dependent differences in expression of GBP5, GBP6, CCHCR1 and CMPK2 affect viremia levels or weight gain in response to PRRSV infection.
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Lough, Graham; Rashidi, Hamed; Kyriazakis, Ilias; Dekkers, Jack C M; Hess, Andrew; Hess, Melanie; Deeb, Nader; Kause, Antti; Lunney, Joan K; Rowland, Raymond R R; Mulder, Han A; Doeschl-Wilson, Andrea;
A host can adopt two response strategies to infection: resistance (reduce pathogen load) and tolerance (minimize impact of infection on performance). Both strategies may be under genetic control and could thus be targeted for genetic improvement. Although there is evidence that supports a genetic basis for resistance to porcine reproductive and respiratory syndrome (PRRS), it is not known whether pigs also differ genetically in tolerance. We determined to what extent pigs that have been shown to vary genetically in resistance to PRRS also exhibit genetic variation in tolerance. Multi-trait linear mixed models and random regression sire models were fitted to PRRS Host Genetics Consortium data from 1320 weaned pigs (offspring of 54 sires) that were experimentally infected with a virulent strain of PRRS virus to obtain genetic parameter estimates for resistance and tolerance. Resistance was defined as the inverse of within-host viral load (VL) from 0 to 21 (VL21) or 0 to 42 (VL42) days post-infection and tolerance as the slope of the reaction-norm of average daily gain (ADG21, ADG42) on VL21 or VL42.Multi-trait analysis of ADG associated with either low or high VL was not indicative of genetic variation in tolerance. Similarly, random regression models for ADG21 and ADG42 with a tolerance slope fitted for each sire did not result in a better fit to the data than a model without genetic variation in tolerance. However, the distribution of data around average VL suggested possible confounding between level and slope estimates of the regression lines. Augmenting the data with simulated growth rates of non-infected half-sibs (ADG0) helped resolve this statistical confounding and indicated that genetic variation in tolerance to PRRS may exist if genetic correlations between ADG0 and ADG21 or ADG42 are low to moderate.Evidence for genetic variation in tolerance of pigs to PRRS was weak when based on data from infected piglets only. However, simulations indicated that genetic variance in tolerance may exist and could be detected if comparable data on uninfected relatives were available. In conclusion, of the two defense strategies, genetics of tolerance is more difficult to elucidate than genetics of resistance.
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| 2016 |
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Schroyen, Martine; Eisley, Christopher; Koltes, James E; Fritz-Waters, Eric; Choi, Igseo; Plastow, Graham S; Guan, Leluo; Stothard, Paul; Bao, Hua; Kommadath, Arun; Reecy, James M; Lunney, Joan K; Rowland, Robert R R; Dekkers, Jack C M; Tuggle, Christopher K;
A region on Sus scrofa chromosome 4 (SSC4) surrounding single nucleotide polymorphism (SNP) marker WUR10000125 (WUR) has been reported to be strongly associated with both weight gain and serum viremia in pigs after infection with PRRS virus (PRRSV). A proposed causal mutation in the guanylate binding protein 5 gene (GBP5) is predicted to truncate the encoded protein. To investigate transcriptional differences between WUR genotypes in early host response to PRRSV infection, an RNA-seq experiment was performed on globin depleted whole blood RNA collected on 0, 4, 7, 10 and 14 days post-infection (dpi) from eight littermate pairs with one AB (favorable) and one AA (unfavorable) WUR genotype animal per litter.Gene Ontology (GO) enrichment analysis of transcripts that were differentially expressed (DE) between dpi across both genotypes revealed an inflammatory response for all dpi when compared to day 0. However, at the early time points of 4 and 7dpi, several GO terms had higher enrichment scores compared to later dpi, including inflammatory response (p < 10(-7)), specifically regulation of NFkappaB (p < 0.01), cytokine, and chemokine activity (p < 0.01). At 10 and 14dpi, GO term enrichment indicated a switch to DNA damage response, cell cycle checkpoints, and DNA replication. Few transcripts were DE between WUR genotypes on individual dpi or averaged over all dpi, and little enrichment of any GO term was found. However, there were differences in expression patterns over time between AA and AB animals, which was confirmed by genotype-specific expression patterns of several modules that were identified in weighted gene co-expression network analyses (WGCNA). Minor differences between AA and AB animals were observed in immune response and DNA damage response (p = 0.64 and p = 0.11, respectively), but a significant effect between genotypes pointed to a difference in ion transport/homeostasis and the participation of G-coupled protein receptors (p = 8e-4), which was reinforced by results from regulatory and phenotypic impact factor analyses between genotypes.We propose these pathway differences between WUR genotypes are the result of the inability of the truncated GBP5 of the AA genotyped pigs to inhibit viral entry and replication as quickly as the intact GBP5 protein of the AB genotyped pigs.
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Wilkinson, Jamie M; Ladinig, Andrea; Bao, Hua; Kommadath, Arun; Stothard, Paul; Lunney, Joan K; Harding, John C S; Plastow, Graham S;
Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection of pregnant females causes fetal death and increased piglet mortality, but there is substantial variation in the extent of reproductive pathology between individual dams. This study used RNA-sequencing to characterize the whole blood transcriptional response to type 2 PRRSV in pregnant gilts during the first week of infection (at 0, 2, and 6 days post-inoculation), and attempted to identify gene expression signatures associated with a low or high level of fetal mortality rates (LFM and HFM; n = 8/group) at necropsy, 21 days post-inoculation. The initial response to infection measured at 2 days post-inoculation saw an upregulation of genes involved in innate immunity, such as interferon-stimulated antiviral genes and inflammatory markers, and apoptosis. A concomitant decrease in expression of protein synthesis and T lymphocyte markers was observed. By day 6 the pattern had reversed, with a drop in innate immune signaling and an increase in the expression of genes involved in cell division and T cell signaling. Differentially expressed genes (DEGs) associated with extremes of litter mortality rate were identified at all three time-points. Among the 15 DEGs upregulated in LFM gilts on all three days were several genes involved in platelet function, including integrins ITGA2B and ITGB3, and the chemokine PF4 (CXCL4). LFM gilts exhibited a higher baseline expression of interferon-stimulated and pro-inflammatory genes prior to infection, and of T cell markers two days post-infection, indicative of a more rapid progression of the immune response to PRRSV. This study has increased our knowledge of the early response to PRRSV in the blood of pregnant gilts, and could ultimately lead to the development of a biomarker panel that can be used to predict PRRSV-associated reproductive pathology.
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Wilkinson, Jamie M; Bao, Hua; Ladinig, Andrea; Hong, Linjun; Stothard, Paul; Lunney, Joan K; Plastow, Graham S; Harding, John C S;
Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection of pregnant pigs can result in congenital infection and ultimately fetal death. Little is known about immune responses to infection at the maternal-fetal interface and in the fetus itself, or the molecular events behind virus transmission and disease progression in the fetus. To investigate these processes, RNA-sequencing of two sites, uterine endothelium with adherent placental tissue and fetal thymus, was performed 21 days post-challenge on four groups of fetuses selected from a large PRRSV challenge experiment of pregnant gilts: control (CON), uninfected (UNINF), infected (INF), and meconium-stained (MEC) (n = 12/group). Transcriptional analyses consisted of multiple contrasts between groups using two approaches: differential gene expression analysis and weighted gene co-expression network analysis (WGCNA). Biological functions, pathways, and regulators enriched for differentially expressed genes or module members were identified through functional annotation analyses. Expression data were validated by reverse transcription quantitative polymerase chain reaction (RTqPCR) carried out for 16 genes of interest.The immune response to infection in endometrium was mainly adaptive in nature, with the most upregulated genes functioning in either humoral or cell-mediated immunity. In contrast, the expression profile of infected fetal thymus revealed a predominantly innate immune response to infection, featuring the upregulation of genes regulated by type I interferon and pro-inflammatory cytokines. Fetal infection was associated with an increase in viral load coupled with a reduction in T cell signaling in the endometrium that could be due to PRRSV-controlled apoptosis of uninfected bystander cells. There was also evidence for a reduction in TWIST1 activity, a transcription factor involved in placental implantation and maturation, which could facilitate virus transmission or fetal pathology through dysregulation of placental function. Finally, results suggested that events within the fetus could also drive fetal pathology. Thymus samples of meconium-stained fetuses exhibited an increase in the expression of pro-inflammatory cytokine and granulocyte genes previously implicated in swine infectious disease pathology.This study identified major differences in the response to PRRSV infection in the uterine endometrium and fetus at the gene expression level, and provides insight into the molecular basis of virus transmission and disease progression.
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Hess, Andrew S; Islam, Zeenath; Hess, Melanie K; Rowland, Raymond R R; Lunney, Joan K; Doeschl-Wilson, Andrea; Plastow, Graham S; Dekkers, Jack C M;
Porcine reproductive and respiratory syndrome (PRRS) is one of the most important swine diseases in the world and genetic selection of pigs for increased resistance to PRRS is an attractive method to improve the health status of the swine herd. This study compared phenotypic and genetic responses to infection with one of two genetically distinct type 2 PRRS virus (PRRSV) isolates: NVSL-97-7895 (NVSL) and KS-2006-72109 (KS06), and evaluated whether the single nucleotide polymorphism (SNP) WUR10000125 (WUR) on chromosome 4 that was associated with viral load and weight gain under infection with NVSL also has an effect on response to infection across North American PRRSV isolates. Wood's lactation curve was fitted to repeated viremia measurements to derive five curve characteristics that were evaluated. 0.05). Genetic correlations of host response between isolates were strong for VL, WG and PV. Accounting for WUR genotype had little impact on these correlations, suggesting that response to PRRSV infection has a substantial polygenic component that is common between these two isolates.These results suggest that the KS06 PRRSV isolate is less virulent than NVSL but that genetic selection for increased resistance to either of these genetically distinct isolates is expected to increase resistance to the other isolate.
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| 2015 |
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Ladinig, Andrea; Detmer, Susan E; Clarke, Kyle; Ashley, Carolyn; Rowland, Raymond R R; Lunney, Joan K; Harding, John C S;
P < 0.06). Inoculation with NVSL 97-7895 induced higher levels of all three cytokines. All three PRRSV isolates were able to induce high mean viral load in individual litters, which was closely related to the proportion of PRRSV positive fetuses in the litter. Viral load in fetal samples was also positively associated with viral load at the maternal-fetal interface. All but one dead fetus were positive for PRRSV RNA, and higher concentrations of PRRSV RNA in fetal thymus increased the odds of fetal death. Our results suggest that virus replication in fetal tissues and the maternal-fetal interface, but not in other gilt tissues, are important for the outcome of reproductive PRRS. Additionally, our data indicate that umbilical lesions decreased corresponding to the use of pentobarbital sedation prior to euthanasia of pregnant gilts by captive bolt.
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Koltes, James E; Fritz-Waters, Eric; Eisley, Chris J; Choi, Igseo; Bao, Hua; Kommadath, Arun; Serão, Nick V L; Boddicker, Nicholas J; Abrams, Sam M; Schroyen, Martine; Loyd, Hyelee; Tuggle, Chris K; Plastow, Graham S; Guan, Leluo; Stothard, Paul; Lunney, Joan K; Liu, Peng; Carpenter, Susan; Rowland, Robert R R; Dekkers, Jack C M; Reecy, James M;
Previously, we identified a major quantitative trait locus (QTL) for host response to Porcine Respiratory and Reproductive Syndrome virus (PRRSV) infection in high linkage disequilibrium (LD) with SNP rs80800372 on Sus scrofa chromosome 4 (SSC4).Within this QTL, guanylate binding protein 5 (GBP5) was differentially expressed (DE) (p < 0.05) in blood from AA versus AB rs80800372 genotyped pigs at 7,11, and 14 days post PRRSV infection. All variants within the GBP5 transcript in LD with rs80800372 exhibited allele specific expression (ASE) in AB individuals (p < 0.0001). A transcript re-assembly revealed three alternatively spliced transcripts for GBP5. An intronic SNP in GBP5, rs340943904, introduces a splice acceptor site that inserts five nucleotides into the transcript. Individuals homozygous for the unfavorable AA genotype predominantly produced this transcript, with a shifted reading frame and early stop codon that truncates the 88 C-terminal amino acids of the protein. RNA-seq analysis confirmed this SNP was associated with differential splicing by QTL genotype (p < 0.0001) and this was validated by quantitative capillary electrophoresis (p < 0.0001). The wild-type transcript was expressed at a higher level in AB versus AA individuals, whereas the five-nucleotide insertion transcript was the dominant form in AA individuals. Splicing and ASE results are consistent with the observed dominant nature of the favorable QTL allele. The rs340943904 SNP was also 100 % concordant with rs80800372 in a validation population that possessed an alternate form of the favorable B QTL haplotype.GBP5 is known to play a role in inflammasome assembly during immune response. However, the role of GBP5 host genetic variation in viral immunity is novel. These findings demonstrate that rs340943904 is a strong candidate causal mutation for the SSC4 QTL that controls variation in host response to PRRSV.
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Schroyen, Martine; Steibel, Juan P; Koltes, James E; Choi, Igseo; Raney, Nancy E; Eisley, Christopher; Fritz-Waters, Eric; Reecy, James M; Dekkers, Jack C M; Rowland, Robert R R; Lunney, Joan K; Ernst, Catherine W; Tuggle, Christopher K;
The presence of variability in the response of pigs to Porcine Reproductive and Respiratory Syndrome virus (PRRSv) infection, and recent demonstration of significant genetic control of such responses, leads us to believe that selection towards more disease resistant pigs could be a valid strategy to reduce its economic impact on the swine industry. To find underlying molecular differences in PRRS susceptible versus more resistant pigs, 100 animals with extremely different growth rates and viremia levels after PRRSv infection were selected from a total of 600 infected pigs. A microarray experiment was conducted on whole blood RNA samples taken at 0, 4 and 7 days post infection (dpi) from these pigs. From these data, we examined associations of gene expression with weight gain and viral load phenotypes. The single nucleotide polymorphism (SNP) marker WUR10000125 (WUR) on the porcine 60 K SNP chip was shown to be associated with viral load and weight gain after PRRSv infection, and so the effect of the WUR10000125 (WUR) genotype on expression in whole blood was also examined.Limited information was obtained through linear modeling of blood gene differential expression (DE) that contrasted pigs with extreme phenotypes, for growth or viral load or between animals with different WUR genotype. However, using network-based approaches, molecular pathway differences between extreme phenotypic classes could be identified. Several gene clusters of interest were found when Weighted Gene Co-expression Network Analysis (WGCNA) was applied to 4 dpi contrasted with 0 dpi data. The expression pattern of one such cluster of genes correlated with weight gain and WUR genotype, contained numerous immune response genes such as cytokines, chemokines, interferon type I stimulated genes, apoptotic genes and genes regulating complement activation. In addition, Partial Correlation and Information Theory (PCIT) identified differentially hubbed (DH) genes between the phenotypically divergent groups. GO enrichment revealed that the target genes of these DH genes are enriched in adaptive immune pathways.There are molecular differences in blood RNA patterns between pigs with extreme phenotypes or with a different WUR genotype in early responses to PRRSv infection, though they can be quite subtle and more difficult to discover with conventional DE expression analyses. Co-expression analyses such as WGCNA and PCIT can be used to reveal network differences between such extreme response groups.
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Ladinig, Andrea; Ashley, Carolyn; Detmer, Susan E; Wilkinson, Jamie M; Lunney, Joan K; Plastow, Graham; Harding, John C S;
Minimal research has focused on understanding mechanisms underlying porcine reproductive and respiratory syndrome virus (PRRSV) induced reproductive failure. We have completed a large-scale project investigating phenotypic and genotypic predictors of reproductive PRRS severity in which numerous clinical, pathological, immunologic and viral responses were characterized in dams and fetuses. The goal was to determine which phenotypic responses were associated with fetal viral load and death after experimental infection of pregnant gilts with type 2 PRRSV, thereby elucidating mechanisms of reproductive PRRS in third trimester pregnant gilts. The presence of fetal infection and increasing RNA concentration at the maternal-fetal interface were strong predictors of the probability of fetal death, while PRRSV RNA concentration in dam sera and systemic tissues were not associated with the odds of fetal death. Fetal infection and death clustered, indicating that the status of adjacent fetuses is crucial for lateral transmission and fetal outcome. Several systemic immune responses of gilts were associated with fetal outcome and viral load: interferon-α contributed to the probability of fetal death, but absolute numbers of T helper cells in early infection, absolute numbers of myeloid cells over time and interleukin 12 levels appeared protective. These results suggest specific immune responses may either contribute to, or protect against, transplacental virus transmission. The WUR10000125 SNP on chromosome 4, associated with PRRS resilience in nursery pigs, was not associated with reproductive outcome. Whereas past research suggested that fetal death results from events occurring at the maternal-fetal interface, we conclude that viral replication within fetuses and spread of PRRSV to adjacent fetuses are pivotal events in the pathogenesis of reproductive PRRS.
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Niederwerder, Megan C; Bawa, Bhupinder; Serão, Nick V L; Trible, Benjamin R; Kerrigan, Maureen A; Lunney, Joan K; Dekkers, Jack C M; Rowland, Raymond R R;
Coinfections involving porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) contribute to a group of disease syndromes known as porcine circovirus-associated disease (PCVAD). Presumably, PRRSV infection enhances PCV2 replication as a result of modulation of host immunity. The purpose of this study was to evaluate PCV2 replication and pathogenesis in pigs vaccinated with a PRRS modified live virus (MLV) vaccine and subsequently challenged with a combination of PRRSV and PCV2. During the early postchallenge period, the number of pigs with PRRSV-associated clinical signs was decreased, and average daily gain (ADG) was increased, in the vaccinated group, demonstrating the protective effect of PRRS vaccination. However, during the later postchallenge period, more pigs in the vaccinated group showed increased PCV2 viremia, decreased ADG, increased PCVAD clinical signs, and increased mortality. In this disease model, the early benefits of PRRSV vaccination were outweighed by the later amplification of PCVAD.
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| 2014 |
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Boddicker, N J; Garrick, D J; Rowland, R R R; Lunney, J K; Reecy, J M; Dekkers, J C M;
Infectious diseases are costly to the swine industry; porcine reproductive and respiratory syndrome (PRRS) is the most devastating. In earlier work, a quantitative trait locus associated with resistance/susceptibility to PRRS virus was identified on Sus scrofa chromosome 4 using approximately 560 experimentally infected animals from a commercial cross. The favorable genotype was associated with decreased virus load and increased weight gain (WG). The objective here was to validate and further characterize the association of the chromosome 4 region with PRRS resistance using data from two unrelated commercial crossbred populations. The validation populations consisted of two trials each of approximately 200 pigs sourced from different breeding companies that were infected with PRRS virus and followed for 42 days post-infection. Across all five trials, heritability estimates were 0.39 and 0.34 for viral load (VL; area under the curve of log-transformed viremia from 0 to 21 days post-infection) and WG to 42 days post-infection respectively. Effect estimates of SNP WUR10000125 in the chromosome 4 region were in the same directions and of similar magnitudes in the two new trials as had been observed in the first three trials. Across all five trials, the 1-Mb region on chromosome 4 explained 15 percent of genetic variance for VL and 11 percent for WG. The effect of the favorable minor allele at SNP WUR10000125 was dominant. Ordered genotypes for SNP WUR10000125 showed that the effect was present irrespective of whether the favorable allele was paternally or maternally inherited. These results demonstrate that selection for host response to PRRS virus infection could reduce the economic impact of PRRS.
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Boddicker, Nicholas J; Bjorkquist, Angelica; Rowland, Raymond R R; Lunney, Joan K; Reecy, James M; Dekkers, Jack C M;
Host genetics has been shown to play a role in porcine reproductive and respiratory syndrome (PRRS), which is the most economically important disease in the swine industry. A region on Sus scrofa chromosome (SSC) 4 has been previously reported to have a strong association with serum viremia and weight gain in pigs experimentally infected with the PRRS virus (PRRSV). The objective here was to identify haplotypes associated with the favorable phenotype, investigate additional genomic regions associated with host response to PRRSV, and to determine the predictive ability of genomic estimated breeding values (GEBV) based on the SSC4 region and based on the rest of the genome. Phenotypic data and 60 K SNP genotypes from eight trials of ~200 pigs from different commercial crosses were used to address these objectives.Across the eight trials, heritability estimates were 0.44 and 0.29 for viral load (VL, area under the curve of log-transformed serum viremia from 0 to 21 days post infection) and weight gain to 42 days post infection (WG), respectively. Genomic regions associated with VL were identified on chromosomes 4, X, and 1. Genomic regions associated with WG were identified on chromosomes 4, 5, and 7. Apart from the SSC4 region, the regions associated with these two traits each explained less than 3% of the genetic variance. Due to the strong linkage disequilibrium in the SSC4 region, only 19 unique haplotypes were identified across all populations, of which four were associated with the favorable phenotype. Through cross-validation, accuracies of EBV based on the SSC4 region were high (0.55), while the rest of the genome had little predictive ability across populations (0.09).Traits associated with response to PRRSV infection in growing pigs are largely controlled by genomic regions with relatively small effects, with the exception of SSC4. Accuracies of EBV based on the SSC4 region were high compared to the rest of the genome. These results show that selection for the SSC4 region could potentially reduce the effects of PRRS in growing pigs, ultimately reducing the economic impact of this disease.
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Ladinig, Andrea; Wilkinson, Jamie; Ashley, Carolyn; Detmer, Susan E; Lunney, Joan K; Plastow, Graham; Harding, John C S;
In spite of extensive research, the mechanisms of reproductive disease associated with Porcine Reproductive and Respiratory Syndrome virus (PRRSv) are still poorly understood. The objectives of this large scale study were to evaluate associations between viral load and fetal preservation, determine the impact of type 2 PRRSv on fetal weights, and investigate changes in ORF5 PRRSv genome in dams and fetuses during a 21-day period following challenge. At gestation day 85 (±1), 114 gilts were experimentally infected with type 2 PRRSv, while 19 gilts served as reference controls. At necropsy, fetuses were categorized according to their preservation status and tissue samples were collected. PRRSv RNA concentrations were measured in gilt serum collected on days 0, 2, 6, and 21 post-infection, as well as in gilt and fetal tissues collected at termination. Fetal mortality was 41±22.8% in PRRS infected litters. Dead fetuses appeared to cluster in some litters but appeared solitary or random in others. Nine percent of surviving piglets were meconium-stained. PRRSv RNA concentration in fetal thymus, fetal serum and endometrium differed significantly across preservation category and was greatest in tissues of meconium-stained fetuses. This, together with the virtual absence of meconium staining in non-infected litters indicates it is an early pathological condition of reproductive PRRS. Viral load in fetal thymus and in fetal serum was positively associated with viral load in endometrium, suggesting the virus exploits dynamic linkages between individual maternal-fetal compartments. Point mutations in ORF5 sequences from gilts and fetuses were randomly located in 20 positions in ORF5, but neither nucleotide nor amino acid substitutions were associated with fetal preservation. PRRSv infection decreased the weights of viable fetuses by approximately 17%. The considerable variation in gilt and fetal outcomes provides tremendous opportunity for more detailed investigations of potential mechanisms and single nucleotide polymorphisms associated with fetal death.
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Ladinig, Andrea; Foxcroft, George; Ashley, Carolyn; Lunney, Joan K; Plastow, Graham; Harding, John C S;
The severity of porcine reproductive and respiratory syndrome was compared in pregnant gilts originating from high and low birth weight litters. One-hundred and eleven pregnant gilts experimentally infected with porcine reproductive and respiratory syndrome virus on gestation day 85 (±1) were necropsied along with their fetuses 21 days later. Ovulation rates and litter size did not differ between groups, but fetuses from low birth weight gilts were shorter, lighter and demonstrated evidence of asymmetric growth with large brain:organ weight ratios (i.e. brain sparing). The number of intrauterine growth retarded fetuses, defined by brain:organ weight ratios greater than 1 standard deviation from the mean, was significantly greater in low, compared to high, birth weight gilts. Although γδ T cells significantly decreased over time in high compared to low birth weight gilts, viral load in serum and tissues, gilt serum cytokine levels, and litter outcome, including the percent dead fetuses per litter, did not differ by birth weight group. Thus, this study provided no substantive evidence that the severity of porcine reproductive and respiratory syndrome is affected by dam birth weight. However, intrauterine growth retarded fetuses had lower viral loads in both fetal thymus and in endometrium adjacent to the umbilical stump. Crown rump length did not significantly differ between fetuses that survived and those that died at least one week prior to termination. Taken together, this study clearly demonstrates that birth weight is a transgenerational trait in pigs, and provides evidence that larger fetuses are more susceptible to transplacental PRRSv infection.
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Choi, Igseo; Bao, Hua; Kommadath, Arun; Hosseini, Afshin; Sun, Xu; Meng, Yan; Stothard, Paul; Plastow, Graham S; Tuggle, Christopher K; Reecy, James M; Fritz-Waters, Eric; Abrams, Samuel M; Lunney, Joan K; Guan, Le Luo;
Transcriptome analysis of porcine whole blood has several applications, which include deciphering genetic mechanisms for host responses to viral infection and vaccination. The abundance of alpha- and beta-globin transcripts in blood, however, impedes the ability to cost-effectively detect transcripts of low abundance. Although protocols exist for reduction of globin transcripts from human and mouse/rat blood, preliminary work demonstrated these are not useful for porcine blood Globin Reduction (GR). Our objectives were to develop a porcine specific GR protocol and to evaluate the GR effects on gene discovery and sequence read coverage in RNA-sequencing (RNA-seq) experiments.A GR protocol for porcine blood samples was developed using RNase H with antisense oligonucleotides specifically targeting porcine hemoglobin alpha (HBA) and beta (HBB) mRNAs. Whole blood samples (n = 12) collected in Tempus tubes were used for evaluating the efficacy and effects of GR on RNA-seq. The HBA and HBB mRNA transcripts comprised an average of 46.1% of the mapped reads in pre-GR samples, but those reads reduced to an average of 8.9% in post-GR samples. Differential gene expression analysis showed that the expression level of 11,046 genes were increased, whereas 34 genes, excluding HBA and HBB, showed decreased expression after GR (FDR <0.05). An additional 815 genes were detected only in post-GR samples.Our porcine specific GR primers and protocol minimize the number of reads of globin transcripts in whole blood samples and provides increased coverage as well as accuracy and reproducibility of transcriptome analysis. Increased detection of low abundance mRNAs will ensure that studies relying on transcriptome analyses do not miss information that may be vital to the success of the study.
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Ladinig, Andrea; Lunney, Joan K; Souza, Carlos J H; Ashley, Carolyn; Plastow, Graham; Harding, John C S;
In spite of extensive research, immunologic control mechanisms against Porcine Reproductive and Respiratory Syndrome virus (PRRSv) remain poorly understood. Cytokine responses have been exhaustively studied in nursery pigs and show contradictory results. Since no detailed reports on cytokine responses to PRRSv in pregnant females exist, the objectives of this study were to compare host cytokine responses between PRRSv-infected and non-infected pregnant gilts, and to investigate relationships between cytokine levels in infected gilts and viral load or fetal mortality rate. Serum samples and supernatants of peripheral blood mononuclear cells (PBMC) either stimulated with PRRSv or phorbol myristate acetate/Ionomycin (PMA/Iono) were analyzed for cytokines/chemokines: interleukins (IL) 1-beta (IL1β), IL4, IL8, IL10, IL12, chemokine ligand 2 (CCL2), interferon alpha (IFNα) and interferon gamma (IFNγ). Three cytokines (IFNα, CCL2, IFNγ) in gilt serum differed significantly in inoculated versus control gilts over time. In supernatants of PRRSv stimulated PBMC from PRRSv-infected gilts, levels of IFNα were significantly decreased, while IL8 secretion was significantly increased. PRRSv infection altered the secretion of all measured cytokines, with the exception of IFNα, from PBMC after mitogen stimulation, indicating a possible immunomodulatory effect of PRRSv. IFNα, CCL2, and IFNγ in serum, and IFNγ in supernatants of PMA/Iono stimulated PBMC were significantly associated with viral load in tissues, serum or both. However, only IFNα in supernatants of PRRSv stimulated PBMC was significantly associated with fetal mortality rate. We conclude that of the eight cytokines tested in this study IFNα was the best indicator of viral load and severity of reproductive PRRSv infection.
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Ladinig, Andrea; Gerner, Wilhelm; Saalmüller, Armin; Lunney, Joan K; Ashley, Carolyn; Harding, John C S;
In spite of more than two decades of extensive research, the understanding of porcine reproductive and respiratory syndrome virus (PRRSv) immunity is still incomplete. A PRRSv infection of the late term pregnant female can result in abortions, early farrowings, fetal death, and the birth of weak, congenitally infected piglets. The objectives of the present study were to investigate changes in peripheral blood mononuclear cell populations in third trimester pregnant females infected with type 2 PRRSv (NVSL 97-7895) and to analyze potential relationships with viral load and fetal mortality rate. PRRSv infection caused a massive, acute drop in total leukocyte counts affecting all PBMC populations by two days post infection. Except for B cells, cell counts started to rebound by day six post infection. Our data also show a greater decrease of naïve B cells, T-helper cells and cytolytic T cells than their respective effector or memory counterparts. Absolute numbers of T cells and γδ T cells were negatively associated with PRRSv RNA concentration in gilt serum over time. Additionally, absolute numbers of T helper cells may be predictive of fetal mortality rate. The preceding three leukocyte populations may therefore be predictive of PRRSv-related pathological outcomes in pregnant gilts. Although many questions regarding the immune responses remain unanswered, these findings provide insight and clues that may help reduce the impact of PRRSv in pregnant gilts.
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| 2013 |
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Zhou, Xiang; Michal, Jennifer J; Zhang, Lifan; Ding, Bo; Lunney, Joan K; Liu, Bang; Jiang, Zhihua;
Secretion of interferons (IFNs) from virus-infected cells is a hallmark of host antiviral immunity and in fact, IFNs exert their antiviral activities through the induction of antiviral proteins. The IFN-induced protein with tetratricopeptide repeats (IFITs) family is among hundreds of IFN-stimulated genes. This family contains a cluster of duplicated loci. Most mammals have IFIT1, IFIT2, IFIT3 and IFIT5; however, bird, marsupial, frog and fish have only IFIT5. Regardless of species, IFIT5 is always adjacent to SLC16A12. IFIT family genes are predominantly induced by type I and type III interferons and are regulated by the pattern recognition and the JAK-STAT signaling pathway. IFIT family proteins are involved in many processes in response to viral infection. However, some viruses can escape the antiviral functions of the IFIT family by suppressing IFIT family genes expression or methylation of 5' cap of viral molecules. In addition, the variants of IFIT family genes could significantly influence the outcome of hepatitis C virus (HCV) therapy. We believe that our current review provides a comprehensive picture for the community to understand the structure and function of IFIT family genes in response to pathogens in human, as well as in animals.
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Christopher-Hennings, Jane; Araujo, Karla P C; Souza, Carlos J H; Fang, Ying; Lawson, Steven; Nelson, Eric A; Clement, Travis; Dunn, Michael; Lunney, Joan K;
Bead-based multiplex assays (BBMAs) are applicable for high throughput, simultaneous detection of multiple analytes in solution (from several to 50-500 analytes within a single, small sample volume). Currently, few assays are commercially available for veterinary applications, but they are available to identify and measure various cytokines, growth factors and their receptors, inflammatory proteins, kinases and inhibitors, neurobiology proteins, and pathogens and antibodies in human beings, nonhuman primates, and rodent species. In veterinary medicine, various nucleic acid and protein-coupled beads can be used in, or for the development of, antigen and antibody BBMAs, with the advantage that more data can be collected using approximately the same amount of labor as used for other antigen and antibody assays. Veterinary-related BBMAs could be used for detection of pathogens, genotyping, measurement of hormone levels, and in disease surveillance and vaccine assessment. It will be important to evaluate whether BBMAs are "fit for purpose," how costs and efficiencies compare between assays, which assays are published or commercially available for specific veterinary applications, and what procedures are involved in the development of the assays. It is expected that many veterinary-related BBMAs will be published and/or become commercially available in the next few years. The current review summarizes the BBMA technology and some of the currently available BBMAs developed for veterinary settings. Some of the human diagnostic BBMAs are also described, providing an example of possible templates for future development of new veterinary-related BBMAs.
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Islam, Zeenath U; Bishop, Stephen C; Savill, Nicholas J; Rowland, Raymond R R; Lunney, Joan K; Trible, Benjamin; Doeschl-Wilson, Andrea B;
Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically significant viral diseases facing the global swine industry. Viremia profiles of PRRS virus challenged pigs reflect the severity and progression of infection within the host and provide crucial information for subsequent control measures. In this study we analyse the largest longitudinal PRRS viremia dataset from an in-vivo experiment. The primary objective was to provide a suitable mathematical description of all viremia profiles with biologically meaningful parameters for quantitative analysis of profile characteristics. The Wood's function, a gamma-type function, and a biphasic extended Wood's function were fit to the individual profiles using Bayesian inference with a likelihood framework. Using maximum likelihood inference and numerous fit criteria, we established that the broad spectrum of viremia trends could be adequately represented by either uni- or biphasic Wood's functions. Three viremic categories emerged: cleared (uni-modal and below detection within 42 days post infection(dpi)), persistent (transient experimental persistence over 42 dpi) and rebound (biphasic within 42 dpi). The convenient biological interpretation of the model parameters estimates, allowed us not only to quantify inter-host variation, but also to establish common viremia curve characteristics and their predictability. Statistical analysis of the profile characteristics revealed that persistent profiles were distinguishable already within the first 21 dpi, whereas it is not possible to predict the onset of viremia rebound. Analysis of the neutralizing antibody(nAb) data indicated that there was a ubiquitous strong response to the homologous PRRSV challenge, but high variability in the range of cross-protection of the nAbs. Persistent pigs were found to have a significantly higher nAb cross-protectivity than pigs that either cleared viremia or experienced rebound within 42 dpi. Our study provides novel insights into the nature and degree of variation of hosts' responses to infection as well as new informative traits for subsequent genomic and modelling studies.
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| 2012 |
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Boddicker, N; Waide, E H; Rowland, R R R; Lunney, J K; Garrick, D J; Reecy, J M; Dekkers, J C M;
Porcine reproductive and respiratory syndrome (PRRS) causes decreased reproductive performance in breeding animals and increased respiratory problems in growing animals, which result in significant economic losses in the swine industry. Vaccination has generally not been effective in the prevention of PRRS, partially because of the rapid mutation rate and evolution of the virus. The objective of the current study was to discover the genetic basis of host resistance or susceptibility to the PRRS virus through a genome-wide association study using data from the PRRS Host Genetics Consortium PRRS-CAP project. Three groups of approximately 190 commercial crossbred pigs from 1 breeding company were infected with PRRS virus between 18 and 28 d of age. Blood samples and BW were collected up to 42 d post infection (DPI). Pigs were genotyped with the Illumina Porcine 60k Beadchip. Whole-genome analysis focused on viremia at each day blood was collected and BW gains from 0 to 21 DPI (WG21) or 42 DPI (WG42). Viral load (VL) was quantified as area under the curve from 0 to 21 DPI. Heritabilities for WG42 and VL were moderate at 0.30 and litter accounted for an additional 14% of phenotypic variation. Genomic regions associated with VL were found on chromosomes 4 and X and on 1, 4, 7, and 17 for WG42. The 1-Mb region identified on chromosome 4 influenced both WG and VL, exhibited strong linkage disequilibrium, and explained 15.7% of the genetic variance for VL and 11.2% for WG42. Despite a genetic correlation of -0.46 between VL and WG42, genomic EBV for this region were favorably and nearly perfectly correlated. The favorable allele for the most significant SNP in this region had a frequency of 0.16 and estimated allele substitution effects were significant (P < 0.01) for each group when the SNP was fitted as a fixed covariate in a model that included random polygenic effects with overall estimates of -4.1 units for VL (phenotypic SD = 6.9) and 2.0 kg (phenotypic SD = 3 kg) for WG42. Candidate genes in this region on SSC4 include the interferon induced guanylate-binding protein gene family. In conclusion, host response to experimental PRRS virus challenge has a strong genetic component, and a QTL on chromosome 4 explains a substantial proportion of the genetic variance in the studied population. These results could have a major impact in the swine industry by enabling marker-assisted selection to reduce the impact of PRRS but need to be validated in additional populations.
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Wysocki, M; Chen, H; Steibel, J P; Kuhar, D; Petry, D; Bates, J; Johnson, R; Ernst, C W; Lunney, J K;
1.96]. Top canonical pathways included acute phase response signalling, crosstalk between dendritic cells and natural killer cells and tight junction signalling, with numerous immune response genes that were upregulated (SOCS1, SOD2, RBP4, HLA-B, HLA-G, PPP2R1A and TAP1) or downregulated (IL18, TF, C4BPA, C1QA, C1QB and TYROBP). One mechanism, regulation of complement activation, may have been blocked in HR (PRRSV-susceptible) pigs and could account for the poor clearance of PRRSV by infected macrophages. Multiple inhibiting signals may have prevented effective immune responses in susceptible HR pigs, although some protective genes were upregulated in these pigs. It is likely that in HR pigs, expression of genes associated with protection was delayed, so that the immune response was not stimulated early; thus, PRRSV infection prevented protective immune responses.
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Arceo, Maria E; Ernst, Catherine W; Lunney, Joan K; Choi, Igseo; Raney, Nancy E; Huang, Tinghua; Tuggle, Christopher K; Rowland, R R R; Steibel, Juan P;
We evaluated differences in gene expression in pigs from the Porcine Reproductive and Respiratory Syndrome (PRRS) Host Genetics Consortium initiative showing a range of responses to PRRS virus infection. Pigs were allocated into four phenotypic groups according to their serum viral level and weight gain. RNA obtained from blood at 0, 4, 7, 11, 14, 28, and 42 days post-infection (DPI) was hybridized to the 70-mer 20K Pigoligoarray. We used a blocked reference design for the microarray experiment. This allowed us to account for individual biological variation in gene expression, and to assess baseline effects before infection (0 DPI). Additionally, this design has the flexibility of incorporating future data for differential expression analysis. We focused on evaluating transcripts showing significant interaction of weight gain and serum viral level. We identified 491 significant comparisons [false discovery rate (FDR) = 10%] across all DPI and phenotypic groups. We corroborated the overall trend in direction and level of expression (measured as fold change) at 4 DPI using qPCR (r = 0.91, p ≤ 0.0007). At 4 and 7 DPI, network and functional analyses were performed to assess if immune related gene sets were enriched for genes differentially expressed (DE) across four phenotypic groups. We identified cell death function as being significantly associated (FDR ≤ 5%) with several networks enriched for DE transcripts. We found the genes interferon-alpha 1(IFNA1), major histocompatibility complex, class II, DQ alpha 1 (SLA-DQA1), and major histocompatibility complex, class II, DR alpha (SLA-DRA) to be DE (p ≤ 0.05) between phenotypic groups. Finally, we performed a power analysis to estimate sample size and sampling time-points for future experiments. We concluded the best scenario for investigation of early response to PRRSV infection consists of sampling at 0, 4, and 7 DPI using about 30 pigs per phenotypic group.
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Rowland, Raymond R R; Lunney, Joan; Dekkers, Jack;
Infections caused by porcine reproductive and respiratory syndrome virus (PRRSV) have a severe economic impact on pig production in North America, Europe, and Asia. The emergence and eventual predominance of PRRS in the 1990s are the likely result of changes in the pork industry initiated in the late 1970s, which allowed the virus to occupy a unique niche within a modern commercial production system. PRRSV infection is responsible for severe clinical disease, but can maintain a life-long subclinical infection, as well as participate in several polymicrobial syndromes. Current vaccines lessen clinical signs, but are of limited use for disease control and elimination. The relatively poor protective immunity following vaccination is a function of the virus's capacity to generate a large degree of genetic diversity, combined with several strategies to evade innate and adaptive immune responses. In 2007, the PRRS Host Genetics consortium (PHGC) was established to explore the role of host genetics as an avenue for PRRS control. The PHGC model for PRRS incorporates the experimental infection of large numbers of growing pigs and has created the opportunity to study experimental PRRSV infection at the population level. The results show that pigs can be placed into distinct phenotypic groups, including pigs that show resistance (i.e., low virus load) or pigs that exhibit "tolerance" to infection. Tolerance was illustrated by pigs that gain weight normally in the face of a relatively high virus load. Genome-wide association analysis has identified a region on chromosome 4 (SSC4) correlated with resistance; i.e., lower cumulative virus load within the first 42 days of infection. The genomic region is near a family of genes involved in innate immunity. The region is also associated with higher weight gain in challenged pigs, suggesting that pigs with the resistance alleles don't seem to simultaneously experience reduction in growth, i.e., that resistance and tolerance are not antagonistically related. These results create the opportunity to develop breeding programs that will produce pigs with increased resistance to PRRS and simultaneously high growth rate. The identification of genomic markers involved in actual tolerance will likely prove more difficult, primarily because tolerance is difficult to quantify and because tolerance mechanism are still poorly understood. Another avenue of study includes the identification of genomic markers related to improved response following vaccination.
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| 2011 |
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Lunney, Joan K; Steibel, Juan Pedro; Reecy, James M; Fritz, Eric; Rothschild, Max F; Kerrigan, Maureen; Trible, B; Rowland, Raymond Rr;
Understanding the role of host genetics in resistance to porcine reproductive and respiratory syndrome virus (PRRSV) infection, and the effects of PRRS on pig health and related growth, are goals of the PRRS Host Genetics Consortium (PHGC).The project uses a nursery pig model to assess pig resistance/susceptibility to primary PRRSV infection. To date, 6 groups of 200 crossbred pigs from high health farms were donated by commercial sources. After acclimation, the pigs were infected with PRRSV in a biosecure facility and followed for 42 days post infection (dpi). Blood samples were collected at 0, 4, 7, 10, 14, 21, 28, 35 and 42 dpi for serum and whole blood RNA gene expression analyses; weekly weights were recorded for growth traits. All data have been entered into the PHGC relational database. Genomic DNAs from all PHGC1-6 pigs were prepared and genotyped with the Porcine SNP60 SNPchip.Results have affirmed that all challenged pigs become PRRSV infected with peak viremia being observed between 4-21 dpi. Multivariate statistical analyses of viral load and weight data have identified PHGC pigs in different virus/weight categories. Sera are now being compared for factors involved in recovery from infection, including speed of response and levels of immune cytokines. Genome-wide association studies (GWAS) are underway to identify genes and chromosomal locations that identify PRRS resistant/susceptible pigs and pigs able to maintain growth while infected with PRRSV.Overall, the PHGC project will enable researchers to discover and verify important genotypes and phenotypes that predict resistance/susceptibility to PRRSV infection. The availability of PHGC samples provides a unique opportunity to continue to develop deeper phenotypes on every PRRSV infected pig.
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