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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

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<p> Various areas of studies on the natural and the prosthetic aortic valves are reviewed. </p> <p> A microtensile technique devised to investigate the inhomogeneous and anisotropic material properties of a porcine aortic valve's leaflets is described. Also, the theory and apparatus of a new stereophotogrammetric technique to define points in space by their Cartesian coordinates is introduced. The technique is used to investigate the local surface strains and curvatures of a porcine aortic valve's leaflets from 0 to 120 mm. Hg. in-vitro. </p> <p> It is found that the valve leaflets display marked inhomogeneity and anisotropy (orthotropy is assumed) in the elastic moduli and transition strains. For the non-coronary leaflet, the radial post-transition moduli vary from 42 to 215 gm/mm² with a mean of 111 gm/mm² (s.d. = 43 gm/mm²); and the radial transition strains vary from 30% to 70% with a mean of 58% (s.d. = 7%). Areas nearer the leaflet's coaptation edge tend to exhibit lower radial transition strains than the annulus edge. The central region of the leaflet is found to be the stiffest. For the same non-coronary leaflet, the circumferential post-transition moduli vary from 220 to 590 gm/mm² with a mean of 342 gm/mm² (s.d. = 118 gm/mm²); and the circumferential transition strains vary from 22% to 47% with a mean of 33% (s.d. = 3%). </p> <p> Inhomogeneity between leaflets is also observed; preliminary results seem to suggest that the non-coronary leaflet is the stiffest in the radial direction and the least stiff in the circumferential direction. In comparison, the right coronary leaflet exhibits the largest radial transition strains (~80% ) and the smallest circumferential transition strains (~25%). </p> <p> For the diastolic valve in-vitro, the circumferential strains are less than 10% at all pressures; therefore , this suggests pre-transition behaviour during diastole which is contrary to the general belief. Radial strains at diastole vary from 10% to well over 100% and show a definite tendency to increase from the sinus-annulus edge to the coaptation edge. The non-coronary leaflet is the least strained of the leaflets (10% to 60% at diastole). </p> <p> The determination of pre-or post-transition state at diastole is discussed and the implications of the results on stress analyses and trileaflet valve designs are noted. </p> / Thesis / Master of Engineering (ME)

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Porcine reproductive and respiratory syndrome (PRRS) is a viral disease that has devastated the global swine industry since the mid 1980s. Although modified live vaccines (MLVs) are typically used for the prevention of clinical disease, they are not always fully effective. Additionally, acute PRRS outbreaks, characterized by more severe clinical signs, have appeared in herds that were previously vaccinated. In this dissertation, we further analyzed the pathogenesis of PRRSV through genetic characterization, assay development, and quasispecies evaluation using the PRRSV ORF5 gene while also attempting to develop an improved PRRS vaccine. To explore the possible mechanism for the emergence of acute PRRS, the open reading frame 5 (ORF5) gene encoding the major envelope protein (GP5) of acute PRRSV isolates was characterized. Sequence and phylogenetic analyses revealed that seven of the acute PRRS virus (PRRSV) isolates were related to other N. American PRRSV isolates while one isolate, 98-37120-2, was very closely related to and may have been derived from the MLV, RespPRRS. We also developed a heteroduplex mobility assay (HMA) for quickly identifying PRRSV field isolates with significant nucleotide sequence identities (â d98%) with the MLVs based on the amplification, denaturation, and reannealing of the ORF5 gene of the field isolates with those of MLV reference strains. All of the field isolates that were highly related to RespPRRS (â T2% nucleotide sequence divergence) were identified by the HMA to form homoduplexes with the reference RespPRRS MLV. We also developed a unique strategy for infecting pigs with PRRSV, known as in vivo transfection, by bypassing the traditional in vitro cell culture step required for in vivo studies. We demonstrated that inoculation of RNA transcripts of a PRRSV infectious cDNA clone directly into the lymph nodes and tonsils of pigs produces active PRRSV infection. Using this method, we also examined the quasispecies populations of PRRSV. Finally, we evaluated the ability of Salmonella choleraesuis to express the PRRSV GP5, and tested its immunogenicity in mice. Based on our data, there was no indication of Salmonella replication in the mice or any evidence of antibody production against S. choleraesuis or PRRSV GP5. / Ph. D.

Heat stress and immune challenge are costly issues to the swine industry causing significant loss in production and health including reduced efficiency in muscle accretion and energy utilization. Alterations to metabolism and immune response may participate in these shortcomings. The study objectives were to examine the metabolic profiles and immune status of swine subjected to a dual challenge of thermal stress and porcine reproductive and respiratory syndrome virus (PRRSV). To determine this, pigs were subjected to four treatments: thermo-neutral (22° C; TN), thermo-neutral PRRSV infected (TP), heat stress (HS), and heat stress PRRSV infected (HP), during two experimental phases. The first phase consisted of infecting half the experimental group with PRRSV while the rest remained infection free in thermo-neutral conditions. A second phase further divided infected and non-infected into heated conditions for three days of constant heat (35° C) or TN conditions. Venous blood was collected prior to each phase and before sacrifice to analyze for metabolites. At sacrifice liver and longissimus dorsi skeletal muscle samples were collected for gene expression analysis. Pigs in challenged conditions had increased body temperatures, reduced feed intake, and lighter body weights compared to controls, with greatest detriment to dual challenged pigs. In addition, challenged pigs had increased markers of muscle degradation. In challenged pigs, differences (p<0.05) were observed in the metabolic and cytokine gene expression profiles suggesting heat stress blunts the immune response of viral infection in muscle and liver. In conclusion, heat stress and immune challenge directly and indirectly affect metabolism and cytokine expression and both variables may contribute to decreased growth parameters. / Master of Science

Porcine reproductive and respiratory syndrome (PRRS) is the most significant infectious disease currently affecting the swine industry worldwide. Several inactivated and modified live vaccines (MLV) have been developed to curb PRRSV infections. The unsatisfactory efficacy and safety of these vaccines, drives for the development of new generation PRRS universal vaccines. Virus like particles (VLPs) based vaccines are gaining increasing acceptance compared to subunit vaccines, as they present the antigens in more veritable conformation and are even readily recognized by the immune system. Hepatitis B virus (HBV) core antigen (HBcAg) is very well studied and has been successfully used as a carrier for more than 100 other viral sequences. In this study, hybrid HBcAg VLPs are generated by fusion of the conserved protective epitopes of PRRSV and expressed in E. coli. An optimized purification protocol that overcomes issues from ultracentrifugation is developed to obtain hybrid HBcAg VLP protein from the inclusion bodies. This hybrid HBcAg VLP protein self assembled to 23nm VLPs that were shown to block virus infection of susceptible cells when tested on MARC 145 cells. Therefore, the safety of non-infectious and non-replicable VLPs and production through low-cost E. coli fermentation may make this vaccine competitive against current vaccines on both efficacy and cost. / Master of Science