Magnetized plasma interactions are ubiquitous in astrophysical and laboratory plasmas. Various physical effects have been shown to be important within colliding plasma flows influenced by opposing ...magnetic fields, however, experimental verification of the mechanisms within the interaction region has remained elusive. Here we discuss a laser-plasma experiment whereby experimental results verify that Biermann battery generated magnetic fields are advected by Nernst flows and anisotropic pressure effects dominate these flows in a reconnection region. These fields are mapped using time-resolved proton probing in multiple directions. Various experimental, modelling and analytical techniques demonstrate the importance of anisotropic pressure in semi-collisional, high-β plasmas, causing a reduction in the magnitude of the reconnecting fields when compared to resistive processes. Anisotropic pressure dynamics are crucial in collisionless plasmas, but are often neglected in collisional plasmas. We show pressure anisotropy to be essential in maintaining the interaction layer, redistributing magnetic fields even for semi-collisional, high energy density physics (HEDP) regimes.
Ecological changes affect pathogen epidemiology and evolution and may trigger the emergence of novel diseases. Aquaculture radically alters the ecology of fish and their pathogens. Here we show an ...increase in the occurrence of the bacterial fish disease Flavobacterium columnare in salmon fingerlings at a fish farm in northern Finland over 23 years. We hypothesize that this emergence was owing to evolutionary changes in bacterial virulence. We base this argument on several observations. First, the emergence was associated with increased severity of symptoms. Second, F. columnare strains vary in virulence, with more lethal strains inducing more severe symptoms prior to death. Third, more virulent strains have greater infectivity, higher tissue-degrading capacity and higher growth rates. Fourth, pathogen strains co-occur, so that strains compete. Fifth, F. columnare can transmit efficiently from dead fish, and maintain infectivity in sterilized water for months, strongly reducing the fitness cost of host death likely experienced by the pathogen in nature. Moreover, this saprophytic infectiousness means that chemotherapy strongly select for strains that rapidly kill their hosts: dead fish remain infectious; treated fish do not. Finally, high stocking densities of homogeneous subsets of fish greatly enhance transmission opportunities. We suggest that fish farms provide an environment that promotes the circulation of more virulent strains of F. columnare. This effect is intensified by the recent increases in summer water temperature. More generally, we predict that intensive fish farming will lead to the evolution of more virulent pathogens.
Vaccines rarely provide full protection from disease. Nevertheless, partially effective (imperfect) vaccines may be used to protect both individuals and whole populations. We studied the potential ...impact of different types of imperfect vaccines on the evolution of pathogen virulence (induced host mortality) and the consequences for public health. Here we show that vaccines designed to reduce pathogen growth rate and/or toxicity diminish selection against virulent pathogens. The subsequent evolution leads to higher levels of intrinsic virulence and hence to more severe disease in unvaccinated individuals. This evolution can erode any population-wide benefits such that overall mortality rates are unaffected, or even increase, with the level of vaccination coverage. In contrast, infection-blocking vaccines induce no such effects, and can even select for lower virulence. These findings have policy implications for the development and use of vaccines that are not expected to provide full immunity, such as candidate vaccines for malaria.
Thermoresponsive polyion complex aggregates were obtained by addition of polyacrylic acid to diblock copolymers based on cationic poly(3-acrylamidopropyltrimethylammonium chloride) and ...thermoresponsive poly(N-isopropylacrylamide). Temperature induced structural changes on these objects whose reversibility was related to the macromolecular characteristics of the copolymers.
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The formation of polyion complexes (PICs) comprising thermoresponsive polymers is intended to result in the formation of aggregates that undergo significant structural changes with temperature. Moreover the observed modifications might be critically affected by polymer structure and PICs composition.
Different block copolymers based on cationic poly(3-acrylamidopropyltrimethylammonium chloride) and thermoresponsive poly(N-isopropylacrylamide) were synthesized by aqueous RAFT/MADIX polymerization at room temperature. Addition of poly(acrylic acid) in a controlled fashion led to the formation of PICs aggregates. The structural changes induced by temperature were characterized by differential scanning calorimetry, Nuclear Magnetic Resonance spectroscopy and scattering methods.
Thermoresponsive PICs undergo significant structural changes when increasing temperature above the cloud point of the thermoresponsive block. The reversibility of these phenomena depends strongly on the structural parameters of the block copolymers and on PICs composition.
Immune responses can cause severe disease, despite the role immunity plays in defending against parasitism. Indeed, immunopathology is a remarkably common cause of disease and has strong impacts upon ...both host and parasite fitness. Why has immune-mediated disease not been eliminated by natural selection? What constraints might immunopathology impose upon the evolution of resistance? In this review, we explore two major mechanistic causes of immunopathology in mammals and consider how such disease may have influenced immune system design. We then propose hypotheses that could explain the failure of natural selection to eliminate immunopathology. Finally, we suggest how the evolution of strategies for parasite virulence and host resistance may be shaped by this "double-edged sword" of immunity. Future work may reveal whether immunopathology constrains the evolution of resistance in all host taxa.
Lakes support globally important food webs through algal productivity and contribute significantly to the global carbon cycle. However, predictions of how broad‐scale lake carbon flux and ...productivity may respond to future climate are extremely limited. Here, we used an integrated modeling framework to project changes in lake‐specific and regional primary productivity and carbon fluxes under 21st century climate for thousands of lakes. We observed high uncertainty in whether lakes collectively were to increase or decrease lake CO2 emissions and carbon burial in our modeled region owing to divergence in projected regional water balance among climate models. Variation in projected air temperature influenced projected changes in lake primary productivity (but not CO2 emissions or carbon burial) as warmer air temperatures decreased productivity through reduced lake water volume. Cross‐scale interactions between regional drivers and local characteristics dictated the magnitude and direction of lake‐specific carbon flux and productivity responses to future climate.
Plain Language Summary
Primary production in lakes sustains important aquatic food webs, and, collectively, lakes play an important role in the global carbon cycle and contribute substantially to global greenhouse gas dynamics and resulting changes in climate. Primary production in lakes and net carbon emissions are affected by climate change. In this study, we simulated lake carbon dynamics and algae growth for thousands of lakes in response to future climate scenarios. Projected future lake contributions to regional greenhouse gas emissions and algal growth were uncertain because of wide variation in future temperature and precipitation, especially in summer. Local characteristics (e.g., water flow paths and lake water color) dictated how much and in which direction individual lake greenhouse gas emissions and algal growth responded to future climate, highlighting the need for computer simulations that account for interacting effects of regional climate and local characteristics on lake dynamics.
Key Points
Future regional water balance dictated variation in regional lake CO2 emissions, carbon burial, and primary productivity
Increased air temperature reduced regional lake productivity due to reduced lake volume but had no effect on CO2 emissions or carbon burial
Cross‐scale interactions dictated the magnitude and direction of lake‐specific responses to future climate projections
•It is crucial to assess the outbreak risk when a pathogen arrives in a new population.•We review two methods for estimating outbreak risks and their applications.•We show how these methods can be ...extended for complex outbreak models.•Estimates can be used to guide pathogen surveillance and control.•Development of these approaches is important for outbreak preparedness.
Mathematical models are increasingly used throughout infectious disease outbreaks to guide control measures. In this review article, we focus on the initial stages of an outbreak, when a pathogen has just been observed in a new location (e.g., a town, region or country). We provide a beginner’s guide to two methods for estimating the risk that introduced cases lead to sustained local transmission (i.e., the probability of a major outbreak), as opposed to the outbreak fading out with only a small number of cases. We discuss how these simple methods can be extended for epidemiological models with any level of complexity, facilitating their wider use, and describe how estimates of the probability of a major outbreak can be used to guide pathogen surveillance and control strategies. We also give an overview of previous applications of these approaches. This guide is intended to help quantitative researchers develop their own epidemiological models and use them to estimate the risks associated with pathogens arriving in new host populations. The development of these models is crucial for future outbreak preparedness.
This manuscript was submitted as part of a theme issue on “Modelling COVID-19 and Preparedness for Future Pandemics”.
Bovine digital dermatitis (DD), also known as papillomatous digital dermatitis (foot warts), has been recognized as a major cause of lameness in cattle, with important economic and welfare ...consequences. The evaluation of therapeutic and preventive interventions aiming to control DD infections in dairy cattle is often challenged by the complex multifactorial etiology of the disease. An experimental infection model to induce acute DD lesions in a controlled environment is proposed. The goal was to provide a standard way of reproducing DD infections independent of external factors that could confound the natural course of the disease, such as management practices or infection pressure, resulting in transmission of DD between animals. A group of 4 yearling Holstein heifers free of any clinical evidence of hoof disease was recruited from a commercial dairy farm and housed in an experimental facility in 1 pen with slatted flooring. The hind feet were wrapped to mimic conditions of prolonged moisture (maceration) and reduced access to air (closure) and inoculated at the heel and dewclaw areas with a homogenate of a naturally occurring DD lesion skin biopsy or a culture broth of Treponema spp. After a period of 12 to 25 d, 4 of 6 and 1 of 4 dewclaw areas inoculated with biopsied DD lesion or a Treponema spp. culture, respectively, had gross lesions compatible with DD. Histopathology confirmed the gross diagnosis in the sites inoculated with tissue homogenate. In the site inoculated with Treponema spp. culture broth, histopathology revealed an incipient DD lesion. Treponema spp. were detected by PCR in both naturally occurring DD homogenate and Treponema spp. culture broth inoculation sites. An experimental infection model to induce acute DD in cattle was developed, which may be used to evaluate interventions to control DD and study the pathogenesis of this infectious hoof disease in a controlled manner.
The Ecology of Genetically Diverse Infections Read, Andrew F.; Taylor, Louise H.
Science (American Association for the Advancement of Science),
05/2001, Letnik:
292, Številka:
5519
Journal Article
Recenzirano
Microparasite infections often consist of genetically distinct clonal lineages. Ecological interactions between these lineages within hosts can influence disease severity, epidemiology, and ...evolution. Many medical and veterinary interventions have an impact on genetic diversity within infections, but there is little understanding of the long-term consequences of such interventions for public and animal health. Indeed, much of the theory in this area is based on assumptions contradicted by the available data.
A key challenge for public health policymakers is determining when an infectious disease outbreak has finished. Following a period without cases, an estimate of the probability that no further cases ...will occur in future (the end-of-outbreak probability) can be used to inform whether or not to declare an outbreak over. An existing quantitative approach (the Nishiura method), based on a branching process transmission model, allows the end-of-outbreak probability to be approximated from disease incidence time series, the offspring distribution and the serial interval distribution. Here, we show how the end-of-outbreak probability under the same transmission model can be calculated exactly if data describing who-infected-whom (the transmission tree) are also available (e.g. from contact tracing studies). In that scenario, our novel approach (the traced transmission method) is straightforward to use. We demonstrate this by applying the method to data from previous outbreaks of Ebola virus disease and Nipah virus infection. For both outbreaks, the traced transmission method would have determined that the outbreak was over earlier than the Nishiura method. This highlights that collection of contact tracing data and application of the traced transmission method may allow stringent control interventions to be relaxed quickly at the end of an outbreak, with only a limited risk of outbreak resurgence.
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