Virus shedding kinetics and unconventional virulence tradeoffs

Tradeoff theory, which postulates that virulence provides both transmission costs and benefits for pathogens, has become widely adopted by the scientific community. Although theoretical literature exploring virulence-tradeoffs is vast, empirical studies validating various assumptions still remain sparse. In particular, truncation of transmission duration as a cost of virulence has been difficult to quantify with robust controlled in vivo studies. We sought to fill this knowledge gap by investigating how transmission rate and duration were associated with virulence for infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss). Using host mortality to quantify virulence and viral shedding to quantify transmission, we found that IHNV did not conform to classical tradeoff theory. More virulent genotypes of the virus were found to have longer transmission durations due to lower recovery rates of infected hosts, but the relationship was not saturating as assumed by tradeoff theory. Furthermore, the impact of host mortality on limiting transmission duration was minimal and greatly outweighed by recovery. Transmission rate differences between high and low virulence genotypes were also small and inconsistent. Ultimately, more virulent genotypes were found to have the overall fitness advantage, and there was no apparent constraint on the evolution of increased virulence for IHNV. However, using a mathematical model parameterized with experimental data, it was found that host culling resurrected the virulence tradeoff and provided low virulence genotypes with the advantage. Human-induced or natural culling, as well as host population fragmentation, may be some of the mechanisms by which virulence diversity is maintained in nature. This work highlights the importance of considering non-classical virulence tradeoffs

An inertial range length scale in structure functions

It is shown using experimental and numerical data that within the traditional inertial subrange defined by where the third order structure function is linear that the higher order structure function scaling exponents for longitudinal and transverse structure functions converge only over larger scales, $r>r_S$, where $r_S$ has scaling intermediate between $\eta$ and $\lambda$ as a function of $R_\lambda$. Below these scales, scaling exponents cannot be determined for any of the structure functions without resorting to procedures such as extended self-similarity (ESS). With ESS, different longitudinal and transverse higher order exponents are obtained that are consistent with earlier results. The relationship of these statistics to derivative and pressure statistics, to turbulent structures and to length scales is discussed.Comment: 25 pages, 9 figure

Transient vortex events in the initial value problem for turbulence

A vorticity surge event that could be a paradigm for a wide class of bursting events in turbulence is studied to examine how the energy cascade is established and how this event could serve as a new test of LES turbulence models. This vorticity surge event is tied to the formation of the energy cascade in a direct numerical simulation by the traditional signatures of a turbulent energy cascade such as spectra approaching -5/3 and strongly Beltramized vortex tubes. A coherent mechanism is suggested by the nearly simultaneous development of a maximum of the peak vorticity $\|\omega\|_\infty$, growth of the dissipation, the appearance of a helically aligned local vortex configuration and strong, transient oscillations in the helicity wavenumber spectrum. This coherence is also examined for two LES models, a traditional purely dissipative eddy viscosity model and a modern method (LANS$-\alpha$) that respects the nonlinear transport properties of fluids. Both LES models properly represent the spectral energy and energy dissipation associated with this vorticity surge event. However, only the model that preserves nonlinear fluid transport properties reproduces the helical properties, including Beltrami-like vortex tubes.Comment: 4 pages, 6 figure

Evidence for a singularity in ideal magnetohydrodynamics: implications for fast reconnection

Numerical evidence for a finite-time singularity in ideal 3D magnetohydrodynamics (MHD) is presented. The simulations start from two interlocking magnetic flux rings with no initial velocity. The magnetic curvature force causes the flux rings to shrink until they come into contact. This produces a current sheet between them. In the ideal compressible calculations, the evidence for a singularity in a finite time $t_c$ is that the peak current density behaves like $|J|_\infty \sim 1/(t_c-t)$ for a range of sound speeds (or plasma betas). For the incompressible calculations consistency with the compressible calculations is noted and evidence is presented that there is convergence to a self-similar state. In the resistive reconnection calculations the magnetic helicity is nearly conserved and energy is dissipated.Comment: 4 pages, 4 figure

Evaluation of modified potato starch in diets for the early-weaned pig

Two growth trials were conducted to compare the effectiveness of replacing either corn or lactose with modified potato starches in diets for conventionally and early-weaned pigs. In Exp. 1, 198 pigs (initially 9.4lb and 19 d of age) were used to determine if modified potato starch (potato starch 1) can replace a portion of the lactose in a high nutrient dense diet. Pigs were allotted by weight, gender, and ancestry to each of six dietary treatments with either five or six pigs per pen and six pens per treatment. The control diet contained 10% dried whey (7.2% lactose), 7.5% spray-dried porcine plasma, 2.5% select menhaden fish meal, and 1.75% spray-dried blood meal. Additional treatments were formulated by adding 7 or 14% modified potato starch or lactose in place of com. A positive control diet also was formulated containing 29% dried whey (providing the same amount of lactose as the 10% dried whey plus 14% lactose diet). All diets were formulated to contain 1.5% lysine, and .90% Ca, .80% P, and 17.88% soybean meal and were fed in a meal form. From day 0 to 14 postweaning, increasing dietary lactose tended to linearly improve ADG and ADFI. Added potato starch did not improve ADG compared with pigs fed the control diet, but ADFI increased linearly with increasing potato starch. In Exp. 2, 180 pigs (8.5 lb and 14 d of age) were used to evaluate the effects of two modified potato starches (potato starch 1 or potato starch 2,a further hydrolyzed potato starch with a greater percentage of sugars as either glucose or maltose as a replacement for either com or lactose in a segregated early-weaning diet (SEW). Pigs were fed a control diet containing 15% dried whey, 12% added lactose, 6% porcine plasma, and 6% select menhaden fish meal. Modified potato starch 1 or 2 (12 %) replaced either corn or the added lactose on an equal weight basis. From d 0 to 7 postweaning, pigs fed the modified potato starch 1 had greater ADG and ADFI than those fed modified potato starch 2. Pigs fed diets with either starch substituted for corn had greater ADG than those fed diets with either starch substituted for lactose. From d 0 to 14 and d o to 21, pigs fed diets containing either modified potato starch substituted for corn tended to have greater ADG than those fed the control diet. This appeared to be the result of greater feed intake of pigs fed the diets containing either starch substituted for corn compared with those fed the control diet or diets containing either starch substituted for lactose. Pigs fed diets with either modified starch substituted for lactose had similar ADG as those fed the control diet. In conclusion, these results suggest that potato starch can improve growth performance of pigs when substituted for corn and can replace a portion of the lactose in an SEW diet without adversely affecting performance.; Swine Day, Manhattan, KS, November 17, 199

The effects of experimental potato protein on starter pig growth performance

This study suggested that experimental potato protein can be an effective replacement for a portion of spray-dried animal plasma in starter diets. Pigs fed combinations of experimental potato protein and spray-dried plasma had greater ADG than those fed either protein source alone. In phase II diets, pigs fed experimental potato protein had similar ADG and FIG compared with those fed spray-dried blood meal and select menhaden fish meal.; Swine Day, Manhattan, KS, November 21, 199

Statistics of Dissipation and Enstrophy Induced by a Set of Burgers Vortices

Dissipation and enstropy statistics are calculated for an ensemble of modified Burgers vortices in equilibrium under uniform straining. Different best-fit, finite-range scaling exponents are found for locally-averaged dissipation and enstrophy, in agreement with existing numerical simulations and experiments. However, the ratios of dissipation and enstropy moments supported by axisymmetric vortices of any profile are finite. Therefore the asymptotic scaling exponents for dissipation and enstrophy induced by such vortices are equal in the limit of infinite Reynolds number.Comment: Revtex (4 pages) with 4 postscript figures included via psfi