Browsing by Subject "PRRS"
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Item Assessment of the demographics and network structure of swine populations in relation to regional disease transmission and contro.(2011-06) Wayne, Spencer RCommercial swine production has steadily evolved the into interconnected multi-site production systems of today. As a result, large numbers of growing pigs and breeding animals move from one location to another on a daily basis. The health of the national swine herd has improved dramatically, due in large part to this new production structure; but the increased network size and the long distances travelled pose obvious threats to swine health. As animal agriculture has become more sophisticated, our government resources have not kept up. Available datasets are inaccurate, fragmented, and offer limited definition of the population at risk and its nature. National efforts to improve livestock population data have met considerable public resistance, and as a result, progress has been limited. Knowledge of the populations at risk is of primary importance when trying to define the potential for disease to spread within and between these populations. Disease spreads by non-mechanical means (as in aerosol transmission of PRRS virus) potentiates the need for knowledge of the neighborhood. Given the dynamic and transient nature of our swine populations, the neighborhood's health status is constantly challenged by the most recent delivery of pigs into the neighborhood. The following dissertation seeks to expand the knowledge of swine populations. Current geographic datasets were assessed for accuracy and reliability. In the event of a foreign animal disease outbreak the usefulness of these datasets would be of prime importance, as they will dictate the distribution of resources. Additionally, the use of satellite-derived thermal imagery to verify the presence of commercial swine is described, along with its estimated sensitivity and specificity. Any regional disease elimination program must consider all swine populations, therefore non-commercial populations (specifically, 4H exhibition pigs) are analyzed. Population size, seasonality, caretaker knowledge, presumed and measured health status, and relationship with commercial swine are defined. The physical movement of infected animals across the landscape allows rapid spread of a pathogen to occur. Volume, frequency, and geographic scale of movements will dictate how quickly and thoroughly an epidemic will proceed. For this reason, these are defined and displayed for pig producing areas at different scales.Item Assessment of the demographics and network structure of swine populations in relation to regional disease transmission and control.(2011-06) Wayne, Spencer R.Commercial swine production has steadily evolved the into interconnected multi-site production systems of today. As a result, large numbers of growing pigs and breeding animals move from one location to another on a daily basis. The health of the national swine herd has improved dramatically, due in large part to this new production structure; but the increased network size and the long distances travelled pose obvious threats to swine health. As animal agriculture has become more sophisticated, our government resources have not kept up. Available datasets are inaccurate, fragmented, and offer limited definition of the population at risk and its nature. National efforts to improve livestock population data have met considerable public resistance, and as a result, progress has been limited. Knowledge of the populations at risk is of primary importance when trying to define the potential for disease to spread within and between these populations. Disease spreads by non-mechanical means (as in aerosol transmission of PRRS virus) potentiates the need for knowledge of the neighborhood. Given the dynamic and transient nature of our swine populations, the neighborhood's health status is constantly challenged by the most recent delivery of pigs into the neighborhood. The following dissertation seeks to expand the knowledge of swine populations. Current geographic datasets were assessed for accuracy and reliability. In the event of a foreign animal disease outbreak the usefulness of these datasets would be of prime importance, as they will dictate the distribution of resources. Additionally, the use of satellite-derived thermal imagery to verify the presence of commercial swine is described, along with its estimated sensitivity and specificity. Any regional disease elimination program must consider all swine populations, therefore non-commercial populations (specifically, 4H exhibition pigs) are analyzed. Population size, seasonality, caretaker knowledge, presumed and measured health status, and relationship with commercial swine are defined. The physical movement of infected animals across the landscape allows rapid spread of a pathogen to occur. Volume, frequency, and geographic scale of movements will dictate how quickly and thoroughly an epidemic will proceed. For this reason, these are defined and displayed for pig producing areas at different scales.Item Characterization of the multidomain Nsp2 Replicase protein of porcine reproductive and respiratory syndrome virus.(2008-12) Han, JunThis dissertation focused on understanding the biology of the nonstructural protein 2 (nsp2) of porcine reproductive and respiratory syndrome virus (PRRSV), the etiological agent of porcine reproductive and respiratory syndrome (PRRS). PRRSV nsp2 is a multidomain protein, containing a putative N-terminal cysteine protease PL2 domain, a 500-700aa middle region of unknown function, a transmembrane domain and a C-terminal tail with uncertainty. In this dissertation, we report the following. (i) PRRSV nsp2 is undergoing rapid evolution in field strains exemplified by viral isolates MN184A and B. (ii) We showed that PRRSV nsp2 hypervariable regions aa12-35 and aa324-813 were not essential for viral replication in MARC-145 cells by using a reverse genetics system based on strain VR-2332. In contrast, deletion of the cysteine protease PL2 core domain, the PL2 downstream flanking sequence (aa181-323), the predicted transmembrane domain and the C-terminal domain were lethal to the virus. (iii) We provided evidence that the nsp2 protein encodes an active PL2 protease and mediates nsp2/3 processing in CHO cells with a substrate preference for the dipeptide G1196|G1197. The PL2 protease possessed both trans- and cis-cleavage activities, which could be distinguished by point mutations. Site-directed mutagenesis studies revealed that mutations that caused a specific loss of trans function of the PL2 protease, but not cis activity, were detrimental to the virus. In addition, we showed that the conserved aspartic acid residues (e.g., Asp89) played an important role in the PL2 trans-cleavage activity. (iv) We investigated the proteolytic processing of nsp2 in MARC-145 cells using recombinant PRRSV expressing foreign epitope-tagged nsp2 protein. We showed the presence of the nsp2 protein as different isoforms in PRRSV-infected cells, which appeared to share the same N terminus but differed in their respective C-termini. The nsp2 species emerged almost simultaneously in the early stage of PRRSV infection, were stable and had low turnover rates. Deletion mutagenesis suggested that the smaller nsp2 species (e.g. nsp2d, e and f) were not essential for viral replication in cell culture. Lastly, a cellular protein, heat shock 70kDa protein 5 (HSPA5), was identified as a coimmunoprecipitate of nsp2.Item Epidemiology of PRRS virus in the United States: Monitoring, Detection in Aerosols, and Risk Factors(2015-08) Tousignant, StevenGiven the lack of good epidemiological data regarding the incidence of PRRSV in the US, the objectives of this dissertation were to 1) document and describe spatial and temporal patterns of PRRSV in the US, 2) describe changes in these patterns over time, 3) investigate the frequency of aerosol PRRSV detection under field conditions as a potential means of transmission, 4) identify risk factors of PRRSV and PED infections and 5) identify factors associated with PRRSV introductions on filtered farms. The data in this thesis suggests that PRRSV behaved predictably between 2009 and 2013, when PEDV emerged in the US swine population and PRRS incidence dropped significantly. Additionally, the frequency of detection of aerosolized PRRSV may be a rare, but highly consequential event. High biosecurity is associated with decreased odds of disease, and filtered farms have undergone many modifications in the past decade to further reduce incidence.Item Evaluation of immune management strategies to control and eliminate porcine reproductive and respiratory syndrome virus (PRRSv)(2013-02) Linhares, Daniel Correia LimaPorcine reproductive and respiratory syndrome (PRRS) is an infectious disease caused by PRRS virus (PRRSv). PRRSv is considered one of the most economically important infectious agents in the swine industry worldwide. This thesis evaluated immune management strategies to eliminate PRRSv from breeding herds, assessed the impact of those strategies in production losses, evaluated management risk factors associated with successful PRRSv elimination or failure, and lastly evaluated vaccination as means to reduce virus dissemination from infected growing pig populations. Chapter 2 compared the use of two immunogens as part of load-close-expose programs in regards to the time it takes to reach PRRSv stability (TTS) from infected breeding herds. Results showed that despite the great variability of TTS between enrolled herds, there were some variables associated with shorter TTS. Specifically, herds that used LVI as the method of whole-herd exposure reached TTS earlier than herds that used MLV vaccines. Moreover, herds with history of PRRSv infection in the 3 years prior to our study reached TTS sooner than herds without history of PRRSv in those same 3 years. Furthermore, herds assisted by a specific veterinary clinic reached TTS sooner than all other herds suggesting that there might be management practices associated with shorter TTS. Our results also showed that PRRSv-monitoring must be done repeatedly over time to increase confidence of PRRSv-negative status of weaned piglets. Altogether, those findings represent prove of concept that herds can reach PRRSv stability as soon as 84 days from establishment of LCE. Further studies are needed to better understand specific factors associated with reaching short TTS, such as farm layout, pig flow and implementation of specific management practices during the period of herd closure. Chapter 3 evaluated the effect of attenuated PRRSv vaccine inoculation compared to the use of live-virulent virus inoculation on production performance in breeding herds. It was shown that herds that used MLV vaccine as part of load-close-expose herd closure programs recovered production levels and had a less severe production impact than herds that used LVI. Also, herds that reported previous PRRSv infection reached time to baseline production (TTBP) sooner than herds with no history of PRRSv infection in the previous 3 years. Interestingly, herds assisted by a specific veterinary clinic recovered production faster than other herds, raising the hypothesis that specific management practices could be associated with herd closure effectiveness. The chapter 3 addendum consisted of economic models to assist veterinarians to make informed decisions between LVI and MLV as part of LCE program to eliminate PRRSv. Taking in consideration the future prices for market hogs and pig feed of the next 12 months, and $13.52 loss per pig that is PRRSv-positive, the results suggested that MLV would be a better economical choice. Chapter 4 was a follow-up from the previous 2 chapters and investigated herd-closure practices associated with successful PRRSv-elimination from breeding herds. It showed that the success rate of LCE programs was 76% and 92% for LVI and MLV herds, when failures associated with unrelated PRRSv were excluded from the analysis although these differences were not statistically significant. Moreover, one out of six herds that achieved 90 days of failure to detect PRRSv in due to wean piglets failed to achieve AASV category III, which indicates that more strict monitoring programs should be adopted in herds undergoing PRRSv elimination. Interestingly, herds assisted by different veterinary clinics had different set of recommendations of management practices to be followed during LCE, indicating that there was no agreement between veterinarians on what is the relative importance of each management practice evaluated. The variables associated with failure to reach AASV category III were a) being infected with a PRRSv of RFLP pattern 1-4-4 and b) holding back pigs at weaning for quality. Chapter 5 focused on PRRSv-infected growing pig populations. Growing pig populations are a major source of PRRSv dissemination within regions. The effect of an attenuated PRRSv vaccine was evaluated on shedding and generation of aerosols of a wild-type virus from an infected growing pig population raised under Minnesota's swine industry field conditions. Our results showed that vaccinating acutely PRRSv infected growing pigs with MLV vaccine reduced duration and magnitude of PRRSv detection in aerosols exhausted from the pig barn. Further studies are needed to characterize the effect of implementation (rather than recommendation) of key management practices on the success of PRRSv elimination programs. There is also a need to better understand the procedures to prepare live (virulent) virus inoculum to expose adult animals in load-close-expose programs. For instance, there is a need to document the effect of PRRSv infectivity dose, route of exposure and materials used to dilute the serum on TTS and TTBP. On the growing pig side, there is a need to validate other effective methods to decrease virus dissemination from infected pig sites that continue to pose a risk for neighboring pig populations, for example by inactivating PRRSv in aerosols coming out of infected pig barns. Altogether, the work presented in this thesis provided science-based information on immune management strategies to control and eliminate PRRSv infection from pig populations. Information herein reviewed, discovered, described and discussed has direct implications to the swine industry and can assist veterinarians to choose appropriate strategies to reduce production losses and decrease PRRSv dissemination from infected pig populations.