Research has demonstrated that porcine circovirus type 2 (PCV2) can be shed into boar semen, raising the possibility that artificial insemination may be an important route by which disease associated with PCV2 is transmitted. The objective of this experiment was to determine the effect of vaccination against PCV2 on ejaculate characteristics and PCV2-specific antibody titers in serum of PCV2-positive boars viremia and viral shedding in semen. Semen and blood samples were collected weekly from week 0 to week 8. After collections at week 0, boars were vaccinated with a commercial vaccine against PCV2 (n = 5) (Suvaxyn PCV2 One dose; Fort Dodge Animal Health, Fort Dodge, IA) or served as controls and received 2 ml 0.9% saline (n = 5). Sperm concentrations and characteristics of sperm motility were assessed using a computer-assisted sperm analysis system (Hamilton Thorne Research, Beverly, MA) and sperm morphology was evaluated after staining using light microscopy. The PCV2 antibody titers were determined in serum using an ELISA (Iowa State Veterinary Diagnostic Laboratory; Ames, IA). The genomic copy number of PCV2 DNA in serum and semen was determined by PCR (Iowa State Veterinary Diagnostic Laboratory; Ames, IA). There were no effects of treatment or treatment by week on semen characteristics (P > 0.05). An effect of treatment by week was detected for serum antibody titers (P < 0.01). Compared with controls, antibody titers in vaccinated boars tended to be greater at week 0 (1.13 ± 0.05 titer/ml vs 1.01 ± 0.05 titer/ml; P = 0.09) and were greater at week 2 (1.15 ± 0.05 titer/ml vs 1.01 ± 0.05 titer/ml; P < 0.05) but lesser at week 7 (1.01 ± 0.05 titer/ml vs 1.23 ± 0.05 titer/ml; P < 0.01) and tended to be lesser at week 8 (1.05 ± 0.05 titer/ml vs 1.17 ± 0.05 titer/ml; P = 0.07). There were no effects of treatment, week, or treatment by week for serum genomic copy number of PCV2 DNA (P > 0.1). An effect of week was detected for semen genomic copy number of PCV2 DNA (P < 0.04). During week 3, PCV2 genomic copy number was at its greatest numerical value, however, semen PCV2 genomic copy number was at its lowest point. This was followed by an increase in semen PCV2 genomic copy number during week 7. This increase could be related to the increase in viral shedding in the serum. In summary, vaccination against PCV2 can lower antibody titers when given post-infection and has no effect on indicators of semen fertility. Vaccination also can decrease the length of reoccurring infection by decreasing the length of viral shedding in serum. / Master of Science

Circoviren sind kleine, unbehüllte Viren mit einem einzelsträngigen zirkulären DNA Genom mit eine Größe von 1,7 bis 2,4 kb. Das Porcine Circovirus Typ 2 (PCV2), welches zum Genus Circovirus gehört, ist mit einer Anzahl von Krankheitsmanifestationen verbunden worden, die heute als Porcine Circovirus Assoziierte Krankheiten (PCVAD) zusammengefasst sind. Die PCV2-Infektion bei Rindern ist bis zum jetzigen Zeitpunkt marginal erforscht worden. Serologische Untersuchungen auf Circovirus spezifische Antikörperführten zu widersprüchlichen Ergebnissen. Im Jahr 2007 wurde von der Bovinen Neonatalen Panzytopenie (BNP) in Europa mit unklarer Genese berichtet. Das klinisch - pathologische Bild der Hämorrhagien ähnelte dem Krankheitsbild der Infektiösen Anämie, welche durch ein Circovirus bei Hühnern verursacht wird. Deshalb wurde in dieser Studie eine Breitspektrum PCR zum Nachweis von Cirocvirus-Genomen durchgeführt. In 5 von 25 BNP betroffenen Kälbern konnte circovirale DNA nachgewiesen werden. Das komplette Genom wurde nachfolgend amplifiziert, kloniert und sequenziert. Das nachgewiesene Genom (PCV2-Ha08) hat eine Länge von 1768 Nukleotiden und zeigte eine hohe Homologie (bis zu 99%) mit PCV2-Genotyp b (siehe Publikation 1). Als Ursache der BNP ist vor kurzen die Übertragung von Alloantikörpern über das Kolostrum beschrieben wurden, welche die Zerstörungen von Leukozyten und Thrombozyten sowie deren Vorläuferzellen bewirken. Ungeachtet dessen war es wichtig, die Empfänglichkeit und Immunantwort von Kälbern nach experimenteller Infektion mit PCV2 zu studieren. Für diesen Zweck wurden weitere 181 Proben von BNP-Kälbern aus Deutschland mit Hilfe einer Breitspektrum-PCR getestet. In zwei von 181 Proben wurde PCV2 DNA nachgewiesen. Die vollständigen Sequenzen konnten amplifiziert werden. Während das erste Genom aus einer Blutprobe eines Kalbs in Bayern stammte (PCV2-Ha09), stammte das zweite nachgewiesene Genom aus Lunge und Gehirn von einem Kalb in Sachsen (PCV2-Ha10). Das Genom (PCV2-Ha09) besteht aus 1768 nt, währenddessen das Genom (PCV2-Ha10) aus 1767 nt aufgebaut ist (siehe Publikation 2). Weiterhin wurden die PCV2 Empfänglichkeit und die Immunantwort von Kälbern durch experimentellen PCV2 Inokulation sowie die Möglichkeit, eine Serokonversion nach Impfung mit einer kommerziellen PCV2 Vakzin zu entwickeln, untersucht. PCV2-spezifische Antikörper wurden in den PCV2-infizierten Tieren und in den PCV2-immunisierten Tieren im Tag 11 und 7 nach Inokulation (p.i.) nachgewiesen. PCV2-Genome wurden durch quantitative Realtime-PCR zwischen Tag 4 und Tag 46 p.i. nur in den Blutproben sowie in verschiedenen Geweben (z.B. Milz, Lymphknoten, Thymus) der PCV2-infizierten Tiere nachgewiesen. Das Genom, welches von den Lymphknoten der PCV2-infizierten Kälber erneut isoliert wurde, zeigt eine Identität von 99,9% gegenüber dem Inokulum. Dies weist möglicherweise auf adaptierte Mutationen im PCV2 Genom hin. Die Mutationen C1708T und G365C sind während der Infektionen aufgetreten. Die Sequenzanalyse zeigt eine mögliche adaptierte Mutation an der Aminosäure Nr. 105 in Replikationsgen (Met zu Ile) (siehe Publikation 3). Zusammenfassend kann geschlussfolgert werden, dass der Nachweis der PCV2 Genomen und eine experimentell induzierte Serokonversion möglich war. Es konnte gezeigt werden, dass die Empfänglichkeit von PCV2 nicht allein auf Schweine begrenzt ist und eine Übertragung von PCV2 auf Rinder möglich ist.

Circoviren sind kleine, unbehüllte Viren mit einem einzelsträngigen zirkulären DNA Genom mit eine Größe von 1,7 bis 2,4 kb. Das Porcine Circovirus Typ 2 (PCV2), welches zum Genus Circovirus gehört, ist mit einer Anzahl von Krankheitsmanifestationen verbunden worden, die heute als Porcine Circovirus Assoziierte Krankheiten (PCVAD) zusammengefasst sind. Die PCV2-Infektion bei Rindern ist bis zum jetzigen Zeitpunkt marginal erforscht worden. Serologische Untersuchungen auf Circovirus spezifische Antikörperführten zu widersprüchlichen Ergebnissen. Im Jahr 2007 wurde von der Bovinen Neonatalen Panzytopenie (BNP) in Europa mit unklarer Genese berichtet. Das klinisch - pathologische Bild der Hämorrhagien ähnelte dem Krankheitsbild der Infektiösen Anämie, welche durch ein Circovirus bei Hühnern verursacht wird. Deshalb wurde in dieser Studie eine Breitspektrum PCR zum Nachweis von Cirocvirus-Genomen durchgeführt. In 5 von 25 BNP betroffenen Kälbern konnte circovirale DNA nachgewiesen werden. Das komplette Genom wurde nachfolgend amplifiziert, kloniert und sequenziert. Das nachgewiesene Genom (PCV2-Ha08) hat eine Länge von 1768 Nukleotiden und zeigte eine hohe Homologie (bis zu 99%) mit PCV2-Genotyp b (siehe Publikation 1). Als Ursache der BNP ist vor kurzen die Übertragung von Alloantikörpern über das Kolostrum beschrieben wurden, welche die Zerstörungen von Leukozyten und Thrombozyten sowie deren Vorläuferzellen bewirken. Ungeachtet dessen war es wichtig, die Empfänglichkeit und Immunantwort von Kälbern nach experimenteller Infektion mit PCV2 zu studieren. Für diesen Zweck wurden weitere 181 Proben von BNP-Kälbern aus Deutschland mit Hilfe einer Breitspektrum-PCR getestet. In zwei von 181 Proben wurde PCV2 DNA nachgewiesen. Die vollständigen Sequenzen konnten amplifiziert werden. Während das erste Genom aus einer Blutprobe eines Kalbs in Bayern stammte (PCV2-Ha09), stammte das zweite nachgewiesene Genom aus Lunge und Gehirn von einem Kalb in Sachsen (PCV2-Ha10). Das Genom (PCV2-Ha09) besteht aus 1768 nt, währenddessen das Genom (PCV2-Ha10) aus 1767 nt aufgebaut ist (siehe Publikation 2). Weiterhin wurden die PCV2 Empfänglichkeit und die Immunantwort von Kälbern durch experimentellen PCV2 Inokulation sowie die Möglichkeit, eine Serokonversion nach Impfung mit einer kommerziellen PCV2 Vakzin zu entwickeln, untersucht. PCV2-spezifische Antikörper wurden in den PCV2-infizierten Tieren und in den PCV2-immunisierten Tieren im Tag 11 und 7 nach Inokulation (p.i.) nachgewiesen. PCV2-Genome wurden durch quantitative Realtime-PCR zwischen Tag 4 und Tag 46 p.i. nur in den Blutproben sowie in verschiedenen Geweben (z.B. Milz, Lymphknoten, Thymus) der PCV2-infizierten Tiere nachgewiesen. Das Genom, welches von den Lymphknoten der PCV2-infizierten Kälber erneut isoliert wurde, zeigt eine Identität von 99,9% gegenüber dem Inokulum. Dies weist möglicherweise auf adaptierte Mutationen im PCV2 Genom hin. Die Mutationen C1708T und G365C sind während der Infektionen aufgetreten. Die Sequenzanalyse zeigt eine mögliche adaptierte Mutation an der Aminosäure Nr. 105 in Replikationsgen (Met zu Ile) (siehe Publikation 3). Zusammenfassend kann geschlussfolgert werden, dass der Nachweis der PCV2 Genomen und eine experimentell induzierte Serokonversion möglich war. Es konnte gezeigt werden, dass die Empfänglichkeit von PCV2 nicht allein auf Schweine begrenzt ist und eine Übertragung von PCV2 auf Rinder möglich ist.

Master of Science / Department of Diagnostic Medicine/Pathobiology / Raymond R. R. Rowland / Open reading frame 2 (ORF2) of porcine circovirus type 2 (PCV2) codes for the 233 amino acid capsid protein (CP). Baculovirus-based vaccines that express only ORF2 are protective against clinical disease following experimental challenge or natural infection. The goal of this study was to identify regions in CP preferentially recognized by sera from experimentally infected and vaccinated pigs, and compare these responses to pigs diagnosed with porcine circovirus-associated disease (PCVAD). The approach was to react porcine sera with different CP polypeptide fragments that each contained one or more immunoreactive regions. Expression of polypeptides was performed using E.coli. Initial results showed that sera from vaccinated pigs preferentially recognized only the largest CP(43-233) polypeptide fragment and showed low levels of binding to other CP polypeptide fragments. The results of sera from pigs diagnosed with PMWS showed only minimal reactivity with CP polypeptide fragments, including the largest CP(43-233). PCV2 infected or PDNS diagnosed pigs reacted to all CP polypeptides: however, the strongest reactivity was primarily directed towards CP polypeptides containing residues in the 160-180 region. For this purpose, finer mapping studies were performed. These experiments involved reacting sera from experimentally infected PCV2 pigs and PDNS pigs with overlapping oligopeptides that covered amino acids 141-200. Overall, the results showed a subset of experimentally infected pigs and pigs with PDNS preferentially recognized the CP oligopeptide, 169-STIDYFQPNNKR-180. Alanine scanning identified Y-173, F-174, Q-175 and K-179 as important for antibody recognition. The results from this study support the notion of PCV2 modulation of immunity, including antibody responses that may represent a precursor for disease. The results from this study support the notion of PCV2 modulation of immunity. Furthermore, the methods incorporated in this study provide a means for characterizing the immune response upon vaccination, natural infection and disease.

Porcine circovirus type 2 (PCV2) is a small, non-enveloped, single-stranded DNA virus that causes disease in pigs and is an economically important pathogen affecting pig populations worldwide. PCV2 contains two major open reading frames (ORF): ORF1 encodes two replicase proteins and ORF2 encodes the immunogenic capsid protein. There are three genotypes of PCV2 (PCV2a, PCV2b, and PCV2c), but vaccines available for PCV2 infection are only targeted against PCV2a. The objective of this thesis was to create viable chimeric PCV2 viruses with an ORF2 displaying genetic diversity from all PCV2 genotypes by synthetic DNA shuffling. Variation was identified at 55 amino acid positions in the ORF2 gene among 853 PCV2 capsid gene sequences available in the GenBank database. Degenerate oligonucleotide primers spanning ORF2 were synthesized to contain this naturally observed sequence diversity. Sets of overlapping oligonucleotide primers were fused together using overlap extension PCR to create full-length shuffled ORF2 sequences. The shuffled library of the ORF2 genes was subsequently cloned into the genomic backbone of a wildtype PCV2a infectious DNA clone and transfected into porcine kidney cells (PK-15). After transfection and infection of PK-15 cells, viability of chimeric viruses was screened by immunofluorescence assay (IFA) using anti-PCV2 Rep antibodies. PCR was used to amplify the genomes of viable shuffled viruses from infected cells. PCV2 viruses containing an ORF2 displaying genetic diversity from PCV2a, PCV2b, and PCV2c were isolated in vitro. These shuffled PCV2 viruses may be used as potential candidates for a broadly-protective PCV2 vaccine, although additional studies are warranted to determine in vivo infectivity and pathogenicity. / Master of Science

Made available in DSpace on 2015-03-26T13:46:51Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1965376 bytes, checksum: 32df14418e8fde9c7b4067ac9f8ea6c6 (MD5) Previous issue date: 2010-05-07 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Porcine circovirus 2 (PCV-2) is the major causative agent of postweaning multisystemic wasting syndrome (PMWS) and is associated with different syndromes that affect the swine. The term PCVAD (Porcine circovirus associated diseases) was introduced in 2006 to gather many diseases. Since serological studies are essential for monitoring the virus, the aim of this study was to develop enzyme immunoassays (ELISA) for detection and titration of antibodies to PCV-2 and also for viral quantification as well as the recombinant protein capsid PCV-2 (rCAP PCV-2) in extracts of Escherichia coli. After the standardization of the technique, 29 negative serum samples in ELISA were used for determining the cutt off. The quantitative ELISA was compared with the Immunoperoxidase monolayer (IPMA), through analysis of 155 serum samples, pre-determined by IPMA, of which 125 samples were positive and 30 negative samples for antibodies to PCV-2, in ELISA. The tests showed a concordance of 98.70% confirming the high sensitivity and specificity of ELISA on the IPMA. In the quantitative assay, 20 serum samples had the title determined by ELISA and it showed a higher detection limit of antibodies than the IPMA in 18 of the 20 samples tested. To quantify the rCAP PCV-2 in extracts of E.coli, a capture ELISA was developed. Were used precipitated IgGs from polyclonal rabbit serum anti-rCap PCV-2 as capture antibody and the conjugated IgGs with peroxidases as detection antibody. A standard curve was obtained by serial dilution of rCap PCV-2 and the test showed a detection limit in the range of 0.625 to 0.0097 mg/mL, which was successfully used to quantify the protein in the extract of E.coli. Thus it is expected that this test is also applied in the quantification of future PCV-2 in field samples. / O Circovírus suíno 2 (PCV-2) é o principal agente causador da Síndrome Multissistêmica do Definhamento dos Suínos (SMDS), e está associado a diferentes síndromes que acometem esses animais. O termo PCVAD (Porcine circovírus 2 associated diseases) foi introduzido em 2006, para enquadrar todas essas doenças. Uma vez que estudos sorológicos são fundamentais para o monitoramento do vírus, o objetivo desse trabalho foi desenvolver ensaios imunoenzimáticos (ELISA) para a detecção e titulação de anticorpos anti-PCV-2 e também para a quantificação viral, assim como da proteína recombinante do capsídeo do PCV-2 (rCap PCV-2) em extratos de Escherichia coli . Após a padronização da técnica, 29 amostras de soro negativos por ELISA indireto foram utilizadas para a determinação do cutt off. O ELISA qualitativo foi comparado com a Imunoperoxidase em Monocamada (IPMA), através da análise de 155 amostras de soro, pré-determinadas por IPMA, sendo 125 amostras positivas e 30 amostras negativas para anticorpos anti-PCV-2, no ELISA. Os testes apresentaram uma concordância de 98,70 % confirmando assim a alta sensibilidade e especificidade do ELISA relativa ao IPMA. No ensaio quantitativo, 20 amostras de soro tiveram o título determinado através do ELISA e este apresentou um maior limite de detecção de anticorpos do que o IPMA, em 18 das 20 amostras avaliadas. Para a quantificação da rCap PCV-2 presente em extratos de E.coli, um ELISA de captura foi desenvolvido. Foram utilizadas IgGs precipitadas a partir de soro policlonal de coelho anti-rCap PCV-2 como anticorpo de captura e as IgGs conjugadas com peroxidase como anticorpo de detecção. Uma curva-padrão foi obtida através da diluição seriada da rCap PCV-2 e o ensaio apresentou um limite de detecção na faixa entre 0,625 a 0,0097 μg/mL, que foi utilizado com sucesso para quantificar a proteína no extrato de E.coli. Assim espera-se que este teste seja também aplicado futuramente na quantificação do PCV-2 em amostras de campo.

Porcine circovirus associated disease (PCVAD) is an umbrella term for a multitude of diseases and syndromes that have a negative impact on the health and economics of pig production operations throughout the world. Porcine circovirus type 2 is the causative agent of PCVAD; however the presence of PCV2 alone is rarely enough to cause clinical disease. In order for the full development of PCVAD the presence of a co-infecting pathogen is required. The mechanisms by which co-infection leads to disease remain ongoing areas of research, but it is thought that host immune modulations by PCV2 or a co-infecting pathogen are critical in the pathogenesis of PCVAD. In the first study of this dissertation the ability of PCV2 to induce regulatory T-cells (Tregs) and alter cytokine production was evaluated in vivo. The addition of PCV2 to a multiple viral challenge resulted in a significant increase in Tregs. Levels of IL-10 and IFN-γ were also found to be altered when PCV2 was added to a multiple viral challenge. In further experiments, monocyte derived dendritic cells (MoDC) were infected with different combinations and strains of PCV2 and PRRSV in vitro and evaluated for expression levels of programmed death ligand-1 (PD-L1), IL-10, CD86, swine leukocyte antigen-1 (SLA-1), and swine leukocyte antigen-2 (SLA-2). Expression levels of PD-L1 were significantly increased in PCV2 and PRRSV co-infected MoDCs. SLA-1, SLA-2, and CD86 expression levels were significantly decreased in the MoDC treatment groups containing both PCV2 and virulent stains of PRRSV. MoDC IL-10 expression was significantly increased by PCV2 and virulent strains of PRRSV co-infection. Finally, we investigated the role of the PD-L1/programmed death ligand-1 (PD-1) axis in porcine lymphocyte anergy, apoptosis, and the induction of Tregs. Lymphocyte populations with normal PD-1 expression had significantly higher percentages of anergic and apoptotic lymphocytes, and CD4+CD25HighFoxP3+ Tregs when compared to a PD-1 deficient lymphocyte population. The findings from these studies indicate host immune modulation by PCV2 in vivo and the development of a regulatory phenotype of dendritic cell following PCV2/PRRSV co-infections in vitro that may contribute to a dysfunctional adaptive immune response and the overall pathogenesis of PCVAD. / Ph. D.

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Steven S. Dritz / Vaccination against porcine circovirus type 2 (PCV2) has become a standard practice to improve pig mortality and growth rate in PCV2-affected herds. Unfortunately, there has been little field-based research evaluating factors which affect circovirus vaccination. The focus of this research was on potential vaccination-affecting factors such as age, dosing strategy, pig genetic makeup, and interaction with other vaccines. A total of 6,275 pigs were used to determine factors which affect circovirus vaccination and the effects of vaccination on average daily gain (ADG), immune responses, and viral circulation under field conditions. In the first study evaluating circovirus vaccination effects on PCV2 antibody titer, regardless of age and dose administration protocol, pigs vaccinated with a 2-dose circovirus vaccine had increased (P ≤ 0.008) antibody titers compared with non-vaccinates. In a second study, dosing strategy failed (P = 0.31) to affect antibody titers. However, product and time after vaccination did affect (P = 0.005) antibody titers. In another 130-d study across the nursery and finishing phases, pigs vaccinated with a 2-dose circovirus vaccine had decreased (P < 0.001) serum PCV2 viral load compared with non-vaccinates and ADG of vaccinates was better than non-vaccinates. However, the effect was more pronounced (vaccination-by-genetic interaction, P ≤ 0.05) in Duroc-based compared to Pietrain-based pigs. In a study limited to the nursery phase, vaccination for PCV2 and Mycoplasma hyopneumoniae independently reduced ADG and consumption, but the effect was product-dependent. In a 155-d study across the nursery and finishing phases, vaccination with a 2-dose, 2-vaccine program for PCV2 and Mycoplasma hyopneumoniae decreased (P < 0.001) nursery ADG but tended to increase (P = 0.06) finishing ADG compared to a 1-dose, 2-vaccine program, with no difference (P = 0.66) observed between final pig weights. Finally, circovirus vaccination affected PCV2-circulation in high-health research herds but not in a commercial herd where PCV2 DNA was detected in the environment. These results indicate that finishing performance was improved by a 2-dose circovirus vaccine; however, nursery performance was negatively affected by the same product. Circovirus vaccination responses of growth, viral load, and antibody titer were affected by pig genetic makeup, product, and PCV2-exposure status.

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Joel M. DeRouchey / Steven S. Dritz / A total of 9,979 pigs were used in 11 experiments to quantify production responses under field conditions in growing pigs to PCV2 vaccination, biofuel co-products and dietary supplemental enzymes. Experiments 1 and 2 were conducted to determine the efficacy of a commercial 2-dose Porcine Circovirus Type 2 (PCV2) vaccine. Growth performance and mortality (P < 0.05) of vaccinated pigs improved compared to non-vaccinated pigs in both experiments with the vaccine causing a greater increase in ADG in vaccinated barrows than vaccinated gilts in Exp. 2. Experiment 3 compared the efficacy of 1-dose and 2-dose commercial PCV2 vaccines, where vaccinated pigs had greater ADG (P < 0.05) than vaccinated pigs regardless of vaccine type. The 2-dose group was heavier (P < 0.05) than the control group while the 1-dose group was intermediate. Therefore, PCV2 vaccines were efficacious under field conditions. Experiments 4, 5, and 6 were conducted to evaluate de-oiled corn dried distillers grains with solubles (dDGS) in grow-finish pigs. In Exp. 4, analyzed CP and AA content were higher, but lysine digestibility and energy content were lower in dDGS than traditional dried distillers grains with solubles (DDGS). In Exp. 5, 0 to 30% dDGS in nursery diets did not affect growth performance (P > 0.52). In Exp. 6, 0 to 30% dDGS reduced (linear; P < 0.01) ADG and ADFI, tended to improve (linear; P > 0.07) G:F, decreased (linear; P < 0.01) carcass yield, and increased (linear; P < 0.01) fat iodine values. Experiment 7 was conducted to determine the AA digestibility and energy concentration of novel high-CP distillers co-products from corn (HPC-DDG) and sorghum (HPS-DDGS). Digestibility of AA was higher for HPC-DDG but lower in HPS-DDGS than traditional DDGS. Both co-products had lower energy than traditional DDGS. Finally, Exp. 8, 9, 10, and 11 were used in a meta-analysis to evaluate supplementary dietary enzymes in pigs. Supplemental enzymes, alone or in combination, did not improve grow-finish pig performance (P > 0.58) regardless of dietary DDGS level. In conclusion, these experiments provide important empirical data to quantify production responses of various interventions and dietary ingredients under actual field conditions.

Doctor of Philosophy / Diagnostic Medicine/Pathobiology / Raymond R. R. Rowland / Emerging viral diseases cause significant and widespread economic losses to U.S. swine production. Over the last 25 years, porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2) and porcine epidemic diarrhea virus (PEDV) have emerged or re-emerged, costing the industry billions through increased mortality and clinical or subclinical reductions in growth. Nursery pigs are greatly affected by these viruses due to high susceptibility to primary and secondary infections after weaning. However, clinical disease occurs in only a subpopulation of infected pigs and can vary drastically from sudden death to poor growth performance. This thesis documents a series of 4 studies where nursery pigs were challenged with either PRRSV/PCV2 or PEDV; the associations between clinical outcome and several factors affecting viral pathogenesis were investigated. In the first study, the administration of PRRS modified live virus vaccine prior to co-challenge with PRRSV/PCV2 was shown to protect against PRRS but enhance PCV2 replication and pathogenesis. This study provides insight into the role that PRRS vaccination has in both the control and potentiation of clinical disease. In the second study, microbial populations were compared between pigs with the best and worst clinical outcome following PRRSV/PCV2 co-infection. Increased fecal microbiome diversity was associated with improved clinical outcome; however, worst clinical outcome pigs had prolonged and greater virus replication, highlighting the host response to viral challenge as a primary determinant of clinical outcome. In the third study, 13 clinical phenotypes were compiled for >450 pigs after PRRSV/PCV2 co-infection. Duration of dyspnea and the presence of muscle wasting had the strongest associations with reduced weight gain. This study highlights the opportunity to improve animal welfare and production through improvements in clinical health. In the fourth study, clinical disease was mild to moderate and occurred within the first week after pigs were challenged with PEDV. However, PEDV was detected weeks after clinical disease had resolved and may implicate nursery pigs as an important source of viral carriage and transmission. Overall, the goal of this thesis was to develop models for understanding the impact of emerging and re-emerging viruses to improve recognition and control of disease.