Variable immunity and its consequences for parasite dynamics

Infectious disease represents a growing concern for our developing world. Human diseases result in morbidity, mortality, and suffering. Agricultural diseases can decimate food resources, leading to starvation and economic instability. Wildlife diseases affect the abundance and distribution of species, destabilizing the natural ecosystems on which we rely. Despite these varied contexts, infectious diseases can be united by three common factors: susceptible hosts, parasites, and environmental conditions. Over the past three decades, disease ecology has provided overwhelming evidence that environmental conditions can shape disease risk by altering host-parasite interactions. For example, shifting global temperatures can increase the density of pathogen vectors, thereby increasing pathogen transmission to humans. Such work has long relied on simple mass action principles of transmission, where infections are driven by rates of exposure and hosts are ascribed a single value denoting their susceptibility to infection. However, accumulating evidence suggests that this single value is biologically unrealistic, with most organisms exhibiting considerable variation in their natural levels of susceptibility. Moreover, theoretical models predict that variation in susceptibility can have profound consequences for the spread of disease. Connecting variable susceptibility to its epidemiological outcomes has become an emerging goal in ecology which I have addressed using observation, modeling, and experiments. At the heart of host susceptibility is the immune response. All living organisms are threatened with parasites and, in turn, utilize a suite of immunological defenses to prevent infection. Because immune defenses are important for defeating infections at the individual level, they may also present a barrier to disease transmission at the population level. I have investigated immune defenses and their consequences for parasites in an aquatic host-parasite system: the zooplanktonic host Daphnia dentifera and its fungal pathogen Metschnikowia bicuspidata. In my first chapter, I describe the complete life cycle of Metschnikowia, detail its within-host interactions with Daphnia, and outline the potential defenses Daphnia use to prevent infection. Through Chapter one, I overturned a longstanding assumption that Daphnia cannot recover from infection and developed a series of metrics for quantifying components of the host-parasite interaction. These empirical metrics are specific to the Daphnia-Metschnikowia system, and in my second chapter, I developed a mechanistic modeling approach for estimating host immune defenses that can be applied across wildlife systems. Working closely with Dr. Zoi Rapti, I developed a discrete-state continuous-time Markov model to estimate the probabilities with which organisms resist and clear parasitic infections. In Chapter 3, I quantified the relative importance of Daphnia susceptibility for the emergence of Metschnikowia epidemics. From pre- to peak- epidemic periods, I tracked Metschnikowia exposure and Daphnia recovery rates in six lake ecosystems and found that epidemic emergence depends critically on the interaction between parasite exposure and host susceptibility. In my fourth and final chapter, I tested several hypotheses regarding the nature of Daphnia susceptibility and identified which host traits are the most critical for determining the outcome of infection. Together, my dissertation provides a comprehensive set of empirical studies demonstrating how exposure and susceptibility interact to regulate parasites and the spread of disease in wildlife

An Investigation of Certified Flight Instructor Competencies

The research literature documents distinct differences in teaching skills among instructors in a variety of fields. Some seem to be naturally skilled, whereas others seem to face more challenges in the instructional setting. Although several investigators have addressed a variety of questions concerning flight instructor training, more research is needed to elucidate the instructional competencies associated with successful instruction in this critical field. The proposed poster will present the preliminary results of an observational study designed to identify flight instructor competencies and patterns of instructional behavior. A preliminary set of essential instructor skills was developed based on instructor competencies as defined by the International Board of Standards for Training, Performance and Instruction (Klein, Spector, Grabowski, & de la Teja, 2004). Behaviors specific to flight instruction were then identified. During the Fall semester of 2006, 17 Certified Flight Instructor students were videotaped as they were instructing other students on a flight simulator. The researchers coded the student instructor behaviors using a data collection software product, Noldus Observer. Initial analyses revealed several distinct patterns in flight instructor behaviors. The poster will present the behavioral patterns observed in this study. The ways in which these data may be used to develop further studies to investigate methods of enhancing instructor performance will also be discussed

Prognostic implications of left ventricular hypertrophy

Left ventricular hypertrophy (LVH) was one of the earliest studied echocardiographic characteristics of the left ventricle. As the myriad of measurable metrics has multiplied over recent years, this reliable and relevant variable can often be overlooked. In this paper, we discuss appropriate techniques for accurate analysis, underlying pathophysiology, and the contributions from various risk factors. The prognostic implications of LVH on stroke, serious arrhythmias, and sudden cardiac death are reviewed. Finally, we examine the effect of therapy to reduce LVH and the resultant clinical outcomes. (C) 2018 Elsevier Inc. All rights reserved

Diverging effects of host density and richness across biological scales drive diversity-disease outcomes

AbstractUnderstanding how biodiversity affects pathogen transmission remains an unresolved question due to the challenges in testing potential mechanisms in natural systems and how these mechanisms vary across biological scales. By quantifying transmission of an entire guild of parasites (larval trematodes) within 902 amphibian host communities, we show that the community-level drivers of infection depend critically on biological scale. At the individual host scale, increases in host richness led to fewer parasites per host for all parasite taxa, with no effect of host or predator densities. At the host community scale, however, the inhibitory effects of richness were counteracted by associated increases in total host density, leading to no overall change in parasite densities. Mechanistically, we find that while average host competence declined with increasing host richness, total community competence remained stable due to additive assembly patterns. These results help reconcile disease-diversity debates by empirically disentangling the roles of alternative ecological drivers of parasite transmission and how such effects depend on biological scale.</jats:p

Biodiversity loss underlies the dilution effect of biodiversity

The dilution effect predicts increasing biodiversity to reduce the risk of infection, but the generality of this effect remains unresolved. Because biodiversity loss generates predictable changes in host community competence, we hypothesised that biodiversity loss might drive the dilution effect. We tested this hypothesis by reanalysing four previously published meta-analyses that came to contradictory conclusions regarding generality of the dilution effect. In the context of biodiversity loss, our analyses revealed a unifying pattern: dilution effects were inconsistently observed for natural biodiversity gradients, but were commonly observed for biodiversity gradients generated by disturbances causing losses of biodiversity. Incorporating biodiversity loss into tests of generality of the dilution effect further indicated that scale-dependency may strengthen the dilution effect only when biodiversity gradients are driven by biodiversity loss. Together, these results help to resolve one of the most contentious issues in disease ecology: the generality of the dilution effect.Non peer reviewe

The obesity epidemic and changes in self-report biases in BMI

To assess time trends in measurement error of BMI and the sensitivity/specificity of classifying weight status in the United States by analyzing the difference in BMI between self-reported and measured height and weight

Differential gene expression in response to fungal pathogen exposure in the aquatic invertebrate, 'Daphnia dentifera'

While vertebrate immune systems are appreciated for their complexity and adaptability, invertebrate immunity is often considered to be less complex. However, immune responses in many invertebrates likely involve sophisticated processes. Interactions between the crustacean host Daphnia dentifera and its fungal pathogen Metschnikowia bicuspidata provide an excellent model for exploring the mechanisms underlying crustacean immunity. To explore the genomic basis of immunity in Daphnia, we used RNA‐sequencing technology to quantify differential gene expression between individuals of a single host genotype exposed or unexposed to M. bicuspidata over 24 h. Transcriptomic analyses showed that the number of differentially expressed genes between the control (unexposed) and experimental (exposed) groups increased over time. Gene ontology enrichment analysis revealed that differentially expressed genes were enriched for immune‐related molecules and processes, such as cuticle development, prostaglandin, and defense response processes. Our findings provide a suite of immunologically relevant genes and suggest the presence of a rapidly upregulated immune response involving the cuticle in Daphnia. Studies involving gene expression responses to pathogen exposure shine a light on the processes occurring during the course of infection. By leveraging knowledge on the genetic basis for immunity, immune mechanisms can be more thoroughly understood to refine our understanding of disease spread within invertebrate populations.Published versio