1,721,073 research outputs found
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Avian Roosting Behavior and Vector-Host Contact Rates for West Nile Virus Hosts
Get PDFTransmission of vector-borne disease is driven by contact rates between vectors and hosts. However, little is known about what drives fine-scale variation in mosquito host seeking behavior and the resulting consequences for contact patterns between mosquitoes and their hosts. We examined the roosting behavior of seven avian hosts of West Nile virus (WNV) and patterns of mosquito abundance among communal roost and non-communal roost sites and at different heights where birds roosted. We found some variation in roosting height among avian species coupled with increases in host-seeking mosquito densities higher in the canopy suggesting avian species experience differing vector contact rates influenced by their preferred roosting height. Prior research suggests host-seeking mosquito abundance increase with host group size, however in contrast to a priori predictions, we found significantly fewer host-seeking Culex mosquitoes at American robin communal roosts than non-communal roost sites, and far lower per capita biting mosquitoes and vector-host ratios at roost sites. Focusing specifically on American robins, the preferred host of Culex mosquitoes, our results suggest communal roosting behavior may reduce mosquito-biting rates on roosting individuals. Changes in American robin roosting behavior may partly explain previously observed seasonal changes in feeding patterns of Culex mosquitoes, which has direct implications for the transmission of WNV among birds and humans
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Local to global pathogen and host dynamics of an emerging fungal disease, white-nose syndrome
Get PDFEmerging infectious diseases present a major threat to wildlife populations and have the ability to drive once common species towards extinction. Increasing globalization has resulted in accelerated change in climate, increased anthropogenic movement, and land-use alterations leading to the emergence of infectious diseases in both humans, agriculture and wildlife. Studying disease dynamics at different contexts and scales can provide insight into alternative levers of conservation action. White-nose syndrome, a disease of hibernating bats, was first detected in single tourist cave in northern New York. Pseudogymnoascus destructans the fungal pathogen responsible for WNS has since spread across much of eastern North America causing the collapse of hibernating bat populations. P. destructans was likely introduced to North America from Eurasia, where it is widely distributed, and has likely been present for thousands of years. The data in this dissertation provide insight into the factors determining temporal variation in mortality from WNS. In addition, we will also provide insight into the mechanisms that contribute to species differences in pathogen transmission. More broadly this research provides a synthesis of data across multiple WNS disease contexts, and highlight the substantial conservation insight that can be gained through this approach
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Disease ecology of avian malaria in native and introduced birds in lowland Hawaii
Get PDFNative biodiversity loss and the introduction of exotic species have caused substantial changes in community composition of local communities, with unknown effects on pathogen transmission. Avian malaria (Plasmodium relictum) has driven population declines in native Hawaiian birds, but the role of native and introduced bird species in transmission is poorly understood. Transmission may differ in communities composed primarily of introduced birds compared to communities with natives because natives mount high parasitemia and may have longer-lived infections relative to introduced birds. My dissertation applies fieldwork and molecular tools to investigate the effect of host community composition and land use on malaria transmission in lowland forests on Hawaii Island. In my first chapter, I explore the influence of host community composition on infection prevalence in Culex quinquefasciatus, the primary vector of avian malaria in Hawaii, and examine the reciprocal effect of transmission on the Hawaii amakihi, Chlorodrepanis virens. I found that prevalence in mosquitoes increased with native bird density. Transmission intensity depressed population growth rates of amakihi, but were projected to be above 1 even if incidence was 100%. These results suggest that native birds increase disease transmission, likely because of increased host competence in native compared to introduced birds. In my second chapter, I investigated feeding patterns of Cx. quinquefasciatus and avian malaria infection patterns. I found that Cx. quinquefasciatus fed almost exclusively on birds, with most blood meals coming from Japanese white-eye, Zosterops japonicus, suggesting that ornithophilic feeding by Cx. quinquefasciatus facilitates avian malaria transmission. In my third chapter, I examined land use, larval habitat, and climate drivers of Cx. quinquefasciatus, and another vector species, Aedes albopictus. I found that both species were positively correlated with the proportion of surrounding developed land and the availability of larval habitat, which were themselves positively correlated. These results suggest that conversion of natural habitats to residential and agricultural land may increase larval habitats, with implications for avian malaria transmission in developed areas. This work provides insight into native bird recovery in Hawaii, and underscores the importance of host community composition and land use on the transmission of multi-host vector-borne pathogens
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Developing Tools and Optimizing Control Measures to Reduce Disease Burden During the COVID-19 Pandemic
Get PDFEmerging infectious diseases pose a significant threat to human health. Control measures can reduce the spread and impact of these diseases. Since emerging in November 2019, COVID-19, a respiratory disease caused by the virus SARS-CoV-2, has killed millions of people, disabled many more, and has had devastating economic impacts globally. Two control measures that can reduce the burden of COVID-19 are contact tracing and vaccination. Understanding how and when to apply these measures can improve their efficacy. In my first chapter, we examined the relationship between increasing cases, limited contact tracing capacity, and testing delays on the pathogen reproductive number Rt. We found that Rt increases sigmoidally with the number of cases as tracing capacity is strained. This results in accelerating epidemics as Rt initially increases, despite the reduction in the susceptible population. The sigmoidal relationship shows that contact tracers are most impactful when there is intermediate spread and have nearly no effect in low or high community transmission. In my second chapter, we developed relationships between neutralizing antibody titers and vaccine effectiveness for susceptibility, infectiousness, and death. We used these relationships to quantify the impact that additional mRNA vaccines could have had in reducing transmission and death caused by Delta, the deadliest SARS-CoV-2 variant, in autumn 2021. We found that immunity had significantly waned in vaccine recipients, but a booster dose more than restored protection. Had booster doses been deployed to all eligible recipients in early autumn of 2021, over 100,000 deaths could have been averted.In my third chapter, we used neutralizing antibody titers to predict vaccine effectiveness for a new variant, Omicron. We validated these predictions as traditional vaccine effectiveness estimates became available. We predicted that Omicron increased the risk of hospitalization 2.8-4.4 fold and increased the risk of symptomatic disease 1.7-4.2 fold. All predictions were within 10% of observed estimates, showing that predictive models using neutralizing antibody titers can provide rapid, accurate vaccine effectiveness estimates
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Long-Term Impacts of an Emerging Disease, White-Nose Syndrome: Drivers, Mechanisms, and Conservation Action Influencing the Persistence of North American Bats
Get PDFEmerging infectious diseases can place severe pressures on wildlife populations, leading to major population declines, local extirpation, and species extinctions. However, variability in disease impacts, existing among species and across a spatial and temporal scale, can help us identify species or populations persisting with disease either via resistance, tolerance, pathogen evasion, or by existing within environmental refugia. Understanding mechanisms leading to host persistence can inform conservation management priorities and strategies. White-nose Syndrome (WNS) is a recently emerged disease caused by the fungal pathogen, Pseudogymnoascus destructans (Pd), that has led to severe declines in hibernating bat populations in North America. This work examines patterns and mechanisms associated with variability in WNS impacts with implications for the conservation of affected species. My first chapter investigates spatial heterogeneity in initial impacts of Pd spread across half of continental North America. We found that WNS-related impacts were lessened in the southwestern regions of North America, suggesting potential spatial refugia from WNS-related impacts but only for Perimyotis subflavus. We found that annual air surface temperatures driving Pd growth explained, in part, this spatial variation in WNS-related impacts. Despite evidence for lessened WNS-related declines in the southwest, impacts to bat populations are severe throughout North America for most bat species. My second chapter examines colonies of M. lucifugus that have experienced variability in declines over time, persisting potentially due to host-specific responses. Specifically, I investigate if differences in early winter fat reserves could explain survivorship and persistence of M. lucifugus colonies with WNS. We found that bats persisting with WNS in 2016 were significantly fatter than bats colonies sampled during WNS arrival in 2008 and 2009 at four out of our six sampled sites. At another two sites, we found that bats were either fatter in 2008 and 2009 compared to 2016. We used hibernation energetic models to estimate the amount of fat afforded to survival and found that increased fat reserves from bats measured in 2016 could reduce mortality by 65%. These data suggest that increased fat reserves can explain, in part, the persistence of M. lucifugus colonies with WNS. Lastly, my third chapter experimentally investigates one possible cause of variability in WNS impacts, variation host susceptibility via protective bacteria in the skin microbiome. In this chapter, I explore the efficacy of using a probiotic bacterium, harvested from the skin of a species experiencing lessened WNS impacts, Eptesicus fuscus, as a conservation tool applied to a more highly affected bat species, M. lucifugus. We found relative increases in survival for probiotic-treated groups compared to our sham control group. We also found evidence for decreased fungal infection and severity in probiotic-treated groups. Our results suggest that probiotic treatment can reduce incidence of White-nose Syndrome in M. lucifugus although timing of treatment is an important factor. Together, this work finds that variability in spatial, species-specific, and temporal impacts from WNS can inform conservation efforts. Namely, this work suggests that bat conservation should involve a multi-pronged approach that protects colonies where bats are persisting with WNS via habitat restoration, and potentially treating bats for threatened populations not persisting with WNS. Given the continued threat of WNS to bats as it spreads throughout North America, using a variety of tools to combat this disease may be critical to prevent disease-induced extinction and the local extirpation of affected bat species
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Bacteria isolated from bats inhibit the growth of Pseudogymnoascus destructans, the causative agent of white-nose syndrome
Get PDFEmerging infectious diseases are a key threat to wildlife. Several fungal skin pathogens have recently emerged and caused widespread mortality in vertebrate species, including amphibians, bats, rattlesnakes, and platypus. The importance of the skin microbiome in host-pathogen interactions is increasingly understood to play a large role in determining the course of disease in a host. White-nose syndrome, caused by the fungal skin pathogen Pseudogymnoascus destructans, threatens several hibernating bat species with extinction and there are no known effective treatments. We co-cultured bacteria and P. destructans from the skin microbiome of four bat species to identify bacterial isolates that might inhibit or kill P. destructans. We then conducted two reciprocal challenge experiments in vitro with six candidate bacteria (all in the genus Pseudomonas) that inhibited P. destructans growth across a range of bacterial and fungal concentrations to quantify the effect of these bacteria on the growth of P. destructans. All six Pseudomonas isolates significantly inhibited growth of P. destructans compared to the non-inhibitory control bacteria, and two isolates performed significantly better than others in suppressing P. destructans growth for more than 35 days. In both challenge experiments, the extent of suppression of P. destructans growth was dependent on the concentration of P. destructans and the initial concentration of the bacterial isolate. These results show that bacteria found naturally occurring on bats can inhibit the growth of P. destructans and have promise for development as a biocontrol for bats exposed to white-nose syndrome. In addition, the presence of these bacteria may influence disease outcome among individuals, populations, and species
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Determining the Drivers of Species and Population Extinction in the Emerging Infectious Disease of Bats, White-Nose Syndrome
Get PDFEmerging infectious diseases pose a key threat to wildlife, and the number of diseaseemergence events is increasing. Despite the importance of disease in wildlifeconservation, understanding the drivers of population and species extinction fromdisease has not been tested in an empirical framework. My research incorporatesempirical and theoretical approaches to understand factors that influence pathogentransmission and disease impacts. Here, we focus on the emerging fungal disease ofbats, white-nose syndrome, which has caused widespread declines in bat populationsacross Eastern North America. Our findings highlight the importance of socialbehavior, microclimate conditions, and seasonality in driving impacts from thisdisease. We also identify a species, the Northern long-eared bat, which is likely to goextinct if rapid management action is not taken. These data provide criticalinformation needed to manage wildlife disease epidemics, enabling managementaction prior to species extinction
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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