Strengthening porcine reproductive and respiratory syndrome virus (PRRSV) detection in breeding herds: Development and assessment of processing fluids sampling strategies

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be an outstanding health issue for the global swine production sector. The ability to accurately track the virus and characterize disease status between and within pig populations in today\u27s swine industry is of high importance for the sustainability of the business. Towards that end, the collection of the necessary information to support PRRSV control and elimination programs is dependent upon continuous and reliable monitoring and surveillance systems (MOSS) that need to be both particularly practical and affordable. The issue addressed in this dissertation is the improvement of current PRRSV MOSS employed in breeding herds, through the development of a new sampling method called processing fluids and the assessment and optimization of its applicability for PRRSV RNA and antibody detection in breeding herds. The rational series of studies described below will address the issue pointed above. Chapter Two introduced the processing fluids method as a new tool for PRRSV monitoring in breeding herds. This field study served as a proof of concept for this new sampling technique. Matching sets of processing fluids and serum samples obtained under field conditions from breeding herds, proved that PRRSV can be detected in processing fluids by reverse transcription quantitative polymerase chain reaction (RT-qPCR) at a higher frequency than the standard method of bleeding 30 pigs and testing the serum in pools of five (83.3% vs 66.6%). Moreover, IgG antibody detection was assessed and confirmed, and ORF5 sequencing was also achievable. In Chapter Three, the probability of PRRSV RNA detection in processing fluid samples as a function of the within-litter prevalence of the virus was evaluated and compared with that of serum samples obtained from randomly selected piglets (1, 2, 3 or 4 per litter). Results suggest that when within-litter prevalence is ≥ 50% the probability of PRRSV RNA detection in processing fluids would be higher than that of randomly selected individual piglets (i.e., ≥ 99%). Additional comparisons between the processing fluids sampling approach and the standard PRRSV monitoring scheme using 30 serum samples were made through computer simulation (bootstrapping), giving as result an overall probability of PRRSV detection of 100% when using processing fluids vs 92.1% using 30 serum samples. Chapter Three also looked at processing fluids pooling potential, demonstrating that PRRSV detection was 100% achievable in processing fluids within a low prevalence scenario. The test of a massive pool with only 8% PRRSV-positive pigs (i.e., only 67 viremic pigs out of 834 total pigs in the pool) yielded a strong positive RT-qPCR quantification cycle (Cq) response (Cq = 22.0). The two main objectives of the study described in Chapter Four were, 1) to evaluate the effect of pre-testing conditions of processing fluid samples on RT-qPCR testing results, such as temperatures and time length for sample storage and protocols for nucleic acid extraction and, 2) the adaptation of a commercial PRRSV serum antibody assay (ELISA) for the detection of three different anti-PRRSV antibody (Ab) isotypes (IgM, IgA and IgG) in processing fluids and to establish the test sample-to-positive ratio (S/P) cut-off, i.e., the point that best discriminated positive and negative samples. The two studies within this chapter revealed that, 1) PRRS virus in processing fluid samples would be stable under refrigeration for periods of time of up to 14 days. Also, prolonged exposure to room and higher temperatures would have, correspondingly, a mild and strong detrimental effect on the viral RNA within processing fluid samples, therefore, affecting RT-qPCR testing results. Results also suggested no effect in testing results between the four different commercial RNA purification kits. 2) The results obtained for PRRSV IgG Ab isotype showed perfect discrimination between positive and negative processing fluid samples using a cut-off value of 0.5. Results with the PRRS IgA and IgM ELISA for processing fluids showed low to poor discrimination and therefore would need additional research and optimization. Chapter Five models the effect of pooling processing fluid samples on the probability of PRRSV RNA detection under a low prevalence scenario and establishes the limit for pooling processing fluids where the probability of PRRSV detection would not fall under 95% threshold. PRRSV RNA detection in pooled processing fluid samples of multiple litters (e.g., 29 to 65), is feasible when at least one pig within a given litter in the pool is positive for PRRSV with a RT-qPCR Cq value 29. Thus, demonstrating that, detection limits for pooling processing fluid samples might be dependent on the magnitude of viremia of the pig(s) within the sample. These findings could be useful for designing accurate and reliable processing fluid-based sampling protocols

Residential Consumption of Gas and Electricity in the U.S.: The Role of Prices and Income

We study residential demand for electricity and gas, working with nationwide household-level data that cover recent years, namely 1997-2007. Our dataset is a mixed panel/multi-year cross-sections of dwellings/households in the 50 largest metropolitan areas in the United States as of 2008. To our knowledge, this is the most comprehensive set of data for examining household residential energy usage at the national level, containing the broadest geographical coverage, and with the longest longitudinal component (up to 6 observations per dwelling). We estimate static and dynamic models of electricity and gas demand. We find strong household response to energy prices, both in the short and long term. From the static models, we get estimates of the own price elasticity of electricity demand in the -0.860 to -0.667 range, while the own price elasticity of gas demand is -0.693 to -0.566. These results are robust to a variety of checks. Contrary to earlier literature (Metcalf and Hassett, 1999; Reiss and White, 2005), we find no evidence of significantly different elasticities across households with electric and gas heat. The price elasticity of electricity demand declines with income, but the magnitude of this effect is small. These results are in sharp contrast to much of the literature on residential energy consumption in the United States, and with the figures used in current government agency practice. Our results suggest that there might be greater potential for policies which affect energy price than may have been previously appreciated.Residential Electricity and Gas Demand, Price Elasticity Of Energy Demand, Static Model, Dynamic Panel Data Model, Partial Adjustment Model

Residential Consumption of Gas and Electricity in the U.S.: The Role of Prices and Income

We study residential demand for electricity and gas, working with nationwide household-level data that cover recent years, namely 1997-2007. Our dataset is a mixed panel/multi-year cross-sections of dwellings/households in the 50 largest metropolitan areas in the United States as of 2008. To our knowledge, this is the most comprehensive set of data for examining household residential energy usage at the national level, containing the broadest geographical coverage, and with the longest longitudinal component (up to 6 observations per dwelling). We estimate static and dynamic models of electricity and gas demand. We find strong household response to energy prices, both in the short and long term. From the static models, we get estimates of the own price elasticity of electricity demand in the -0.860 to -0.667 range, while the own price elasticity of gas demand is -0.693 to -0.566. These results are robust to a variety of checks. Contrary to earlier literature (Metcalf and Hassett, 1999; Reiss and White, 2005), we find no evidence of significantly different elasticities across households with electric and gas heat. The price elasticity of electricity demand declines with income, but the magnitude of this effect is small. These results are in sharp contrast to much of the literature on residential energy consumption in the United States, and with the figures used in current government agency practice. Our results suggest that there might be greater potential for policies which affect energy price than may have been previously appreciated.residential electricity and gas demand, price elasticity of energy demand, static model, dynamic panel data model, partial adjustment model

Observational Constraints on Transverse Gravity: a Generalization of Unimodular Gravity

We explore the hypothesis that the set of symmetries enjoyed by the theory that describes gravity is not the full group of diffeomorphisms Diff(M), as in General Relativity, but a maximal subgroup of it, TransverseDiff(M), with its elements having a jacobian equal to unity; at the infinitesimal level, the parameter describing the coordinate change, xi^mu (x), is transverse, i.e., partial_mu(xi^mu)=0. Incidentally, this is the smaller symmetry one needs to propagate consistently a graviton, which is a great theoretical motivation for considering these theories. Also, the determinant of the metric, g, behaves as a "transverse scalar", so that these theories can be seen as a generalization of the better-known unimodular gravity. We present our results on the observational constraints on transverse gravity, in close relation with the claim of equivalence with general scalar-tensor theory. We also comment on the structure of the divergences of the quantum theory to the one-loop order.Comment: Prepared for the First Mediterranean Conference on Classical and Quantum Gravity, MCCQG, Kolymbari (Crete, Greece), 14-18 September, 2009; also, ERE2009: Gravitation in the Large, Bilbao (Spain), 7-11 September, 200

Porcine reproductive and respiratory syndrome monitoring in breeding herds using processing fluids

Processing fluids (PF), the serosanguinous fluid recovered from piglet castration and tail docking, were used for porcine reproductive and respiratory syndrome virus (PRRSV) infection assessment. Processing fluid samples from four breed-to-wean herds were compared with standard sampling protocols, demonstrating PRRSV RNA detection in PF at greater frequency than standard schemes

Use of processing fluid samples for longitudinal monitoring of PRRS virus in herds undergoing virus elimination

This was an observational study that prospectively followed 29 breeding herds for 65 weeks in the U.S.A. that became infected with porcine reproductive and respiratory syndrome virus (PRRSv). The herds operated in a four-week batch farrowing system and adopted a load-close-expose strategy using a modified-live virus vaccine to achieve PRRSv stability. The purpose of this study was to describe time to stability (TTS) based on RT-qPCR testing for PRRSv RNA on processing fluid samples in herds undergoing PRRSv elimination, after implementing herd closure and mass exposure to a PRRS modified-live virus (MLV) vaccine. For the purpose of this study, stability was defined as consistently producing PRRSv-negative pigs. Study herds were monitored until two consecutive piglet batches tested PRRSv RT-qPCR negative, then 30 due-to-wean piglet sera from the second batch were tested for PRRSv RNA by RT-qPCR. Once the farm re-opened, sera from incoming naïve gilts were tested for anti-PRRSv antibodies by ELISA at 30- and 60-days post-entry to confirm negative status to PRRSv. Day zero was the day of whole-herd exposure to a commercial PRRS vaccine virus. Twenty-eight of 29 herds (96.55%) achieved TTS within the study period. TTS ranged from 18 to 55 weeks with a median of 27 weeks. Serum from due-to-wean piglets was collected on 28 farms, of which 26 (92.85%) obtained PRRSv RT-qPCR-negative results on the first collection. At the end of the observational period, 16 sow farms successfully re-introduced PRRSv-naïve gilts with no detected serologic response. In conclusion, the median time to achieve TTS in breeding herds being operated in a four-week batch farrowing system undergoing PRRSv elimination using load-close-expose with attenuated virus vaccine was 27 weeks. Also, processing fluid-based monitoring of breeding herds under PRRS elimination was practical and reliable to assess PRRSv stability

TransverseDiff gravity is to scalar-tensor as unimodular gravity is to General Relativity

Transverse Diffeomorphism (TDiff) theories are well-motivated theories of gravity from the quantum perspective, which are based upon a gauge symmetry principle. The main contribution of this work is to firmly establish a correspondence between TransverseDiff and the better-known scalar-tensor gravity --- in its more general form ---, a relation which is completely analogous to that between unimodular gravity and General Relativity. We then comment on observational aspects of TDiff. In connection with this proof, we derive a very general rule that determines under what conditions the procedure of fixing a gauge symmetry can be equivalently applied before the variational principle leading to the equations of motion, as opposed to the standard procedure, which takes place afterwards; this rule applies to gauge-fixing terms without derivatives.Comment: 10 pages; amsart style; v3: version as appeared in JCAP, redaction improve

Solution generating in scalar-tensor theories with a massless scalar field and stiff perfect fluid as a source

We present a method for generating solutions in some scalar-tensor theories with a minimally coupled massless scalar field or irrotational stiff perfect fluid as a source. The method is based on the group of symmetries of the dilaton-matter sector in the Einstein frame. In the case of Barker's theory the dilaton-matter sector possesses SU(2) group of symmetries. In the case of Brans-Dicke and the theory with "conformal coupling", the dilaton- matter sector has $SL(2,R)$ as a group of symmetries. We describe an explicit algorithm for generating exact scalar-tensor solutions from solutions of Einstein-minimally-coupled-scalar-field equations by employing the nonlinear action of the symmetry group of the dilaton-matter sector. In the general case, when the Einstein frame dilaton-matter sector may not possess nontrivial symmetries we also present a solution generating technique which allows us to construct exact scalar-tensor solutions starting with the solutions of Einstein-minimally-coupled-scalar-field equations. As an illustration of the general techniques, examples of explicit exact solutions are constructed. In particular, we construct inhomogeneous cosmological scalar-tensor solutions whose curvature invariants are everywhere regular in space-time. A generalization of the method for scalar-tensor-Maxwell gravity is outlined.Comment: 10 pages,Revtex; v2 extended version, new parts added and some parts rewritten, results presented more concisely, some simple examples of homogeneous solutions replaced with new regular inhomogeneous solutions, typos corrected, references and acknowledgements added, accepted for publication in Phys.Rev.