Brianna Beechler - Academia.edu (original) (raw)

Papers by Brianna Beechler

Transboundary and Emerging Diseases, Mar 28, 2013

Rift Valley fever (RVF) is an emerging zoonotic mosquito-borne infectious disease that has been i... more Rift Valley fever (RVF) is an emerging zoonotic mosquito-borne infectious disease that has been identified as a risk for spread to other continents and can cause mass livestock mortality. In equatorial Africa, outbreaks of RVF are associated with high rainfall, when vector populations are at their highest. It is, however, unclear how RVF virus persists during the interepidemic periods and between seasons. Understanding interepidemic persistence as well as the role of vectors and hostsis paramount to creating effective management programs for RVF control. We created a mathematical model for the spread of RVF and used the model to explore different scenarios of persistence including vertical transmission and alternate wildlife hosts, with a case study on buffalo in Kruger National Park, South Africa. Our results suggest that RVF persistence is a delicate balance between numerous species of susceptible hosts, mosquito species, vertical transmission, and environmental stochasticity. Further investigations should not focus on a single species, but should instead consider a myriad of susceptible host species when seeking to understand disease dynamics.

PLOS ONE, May 4, 2017

Serum biochemical parameters can be utilized to evaluate the physiological status of an animal, a... more Serum biochemical parameters can be utilized to evaluate the physiological status of an animal, and relate it to the animal's health. In order to accurately interpret individual animal biochemical results, species-specific reference intervals (RI) must be established. Reference intervals for biochemical parameters differ between species, and physiological differences including reproductive status, nutritional resource availability, disease status, and age affect parameters within the same species. The objectives of this study were to (1) establish RI for biochemical parameters in managed African buffalo (Syncerus caffer), (2) assess the effects of age, sex, pregnancy, and season on serum biochemistry values, and (3) compare serum biochemistry values from a managed herd to a free-ranging buffalo herd and to values previously published for captive (zoo) buffalo. Season profoundly affected all biochemistry parameters, possibly due to changes in nutrition and disease exposure. Age also affected all biochemical parameters except gamma glutamyl transferase and magnesium, consistent with patterns seen in cattle. Sex and reproductive status had no detectable effects on the parameters that were measured. The biochemical profiles of managed buffalo were distinct from those observed in the free-ranging herd and captive buffalo. Biochemical differences between buffalo from captive, managed, and free-ranging populations may be related to nutritional restriction or lack of predation in the context of management or captivity. The reference intervals provided in this study, in addition to the seasonal and age-related patterns observed, provide a foundation for health investigations that may inform management strategies in this ecologically and economically important species.

Immunity is one of the most variable phenotypic traits in animals; however, some individuals may ... more Immunity is one of the most variable phenotypic traits in animals; however, some individuals may show less fluctuation in immune traits, resulting in stable patterns of immune variation over time. It is currently unknown whether immune variation has consequences for infectious disease risk. In this study, we identified moderately stable immune traits in wild African buffalo and asked whether the stability of these traits affected bovine tuberculosis (TB) infection risk. We found that adaptive immune traits such as the level of IFN-γ released after white blood cell stimulation, the number of circulating lymphocytes, and the level of antibodies against bovine adenovirus-3 were moderately repeatable (i.e. stable) over time, whereas parameters related to innate immunity either had low repeatability (circulating eosinophil numbers) or were not repeatable (e.g. neutrophil numbers, plasma bacteria killing capacity). Intriguingly, individuals with more repeatable IFN-γ and lymphocyte levels were at a significantly higher risk of acquiring TB infection. In stark contrast, average IFN-γ and lymphocyte levels were poor predictors of TB risk, indicating that immune variability rather than absolute response level better captured variation in disease susceptibility. This work highlights the important and under-appreciated role of immune variability as a predictor of infection risk.

Supplementary results including figures and tables

PLOS ONE, Nov 27, 2019

In this study, we aimed to evaluate to what extent different assays of innate immunity reveal sim... more In this study, we aimed to evaluate to what extent different assays of innate immunity reveal similar patterns of variation across ungulate species. We compared several measures of innate antibacterial immune function across seven different ungulate species using blood samples obtained from captive animals maintained in a zoological park. We measured mRNA expression of two receptors involved in innate pathogen detection, toll-like receptors 2 and 5 (TLR2 and 5), the bactericidal capacity of plasma, as well as the number of neutrophils and lymphocytes. Species examined included aoudad (Ammotragus lervia), American bison (Bison bison bison), yak (Bos grunniens), Roosevelt elk (Cervus canadensis roosevelti), fallow deer (Dama dama), sika deer (Cervus nippon), and Damara zebra (Equus quagga burchellii). Innate immunity varied among ungulate species. However, we detected strong, positive correlations between the different measures of innate immunity-specifically, TLR2 and TLR5 were correlated, and the neutrophil to lymphocyte ratio was positively associated with TLR2, TLR5, and bacterial killing ability. Our results suggest that ecoimmunological study results may be quite robust to the choice of assays, at least for antibacterial innate immunity; and that, despite the complexity of the immune system, important sources of variation in immunity in natural populations may be discoverable with comparatively simple tools.

Authorea (Authorea), Dec 6, 2022

In free-living ecological communities, organismal life histories shape interactions with their en... more In free-living ecological communities, organismal life histories shape interactions with their environment, which ultimately forms the basis of ecological succession. Individual animals in natural populations tend to host diverse parasite species concurrently over their lifetimes. However, the structure and dynamics of mammalian parasite communities have not been contextualized in terms of primary ecological succession, in part because few datasets track occupancy and abundance of multiple parasites in wild hosts starting at birth. Here, we studied community dynamics of twelve subtypes of protozoan microparasites (Theileria spp.) in a herd of African buffalo. We show that Theileria communities followed predictable patterns of succession underpinned by four different parasite life-history strategies. In contrast to many free-living communities, network complexity decreased with host age. Examining parasite communities through the lens of succession may better inform the effect of complex within host eco-evolutionary dynamics on infection outcomes, including parasite coexistence through the lifetime of the host.

Journal of Wildlife Diseases, Apr 21, 2022

Abstract: Measuring inflammatory markers is critical to evaluating both recent infection status a... more Abstract: Measuring inflammatory markers is critical to evaluating both recent infection status and overall human and animal health; however, there are relatively few techniques that do not require specialized equipment or personnel for detecting inflammation among wildlife. Such techniques are useful in that they help determine individual and population-level inflammatory status without the infrastructure and reagents that many more-specific assays require. One such technique, known as the erythrocyte sedimentation rate (ESR), is a measure of how quickly erythrocytes (red blood cells) settle in serum, with a faster rate indicating a general, underlying inflammatory process is occurring. The technique is simple, inexpensive, and can be performed in the field without specialized equipment. We took advantage of a population of African buffalo (Syncerus caffer), well studied from June 2014 to May 2017, to understand the utility of ESR in an important wildlife species. When ESR was compared with other markers of immunity in African buffalo, it correlated to known measures of inflammation. We found that a faster ESR was significantly positively correlated with increased total globulin levels and significantly negatively correlated with increased red blood cell count and albumin levels. We then evaluated if ESR correlated to the incidence of five respiratory pathogens and infection with two tick-borne pathogens in African buffalo. Our results suggest that elevated ESR is associated with the incidence of bovine viral diarrhea virus infection, parainfluenza virus, and Mannheimia haemolytica infections as well as concurrent Anaplasma marginale and Anaplasma centrale coinfection. These findings suggest that ESR is a useful field test as an inflammatory marker in individuals and herds, helping us better monitor overall health status in wild populations.

Parasite Immunology, Apr 27, 2015

In the face of rapid environmental change, anticipating shifts in microparasite and macroparasite... more In the face of rapid environmental change, anticipating shifts in microparasite and macroparasite dynamics, including emergence events, is an enormous challenge. We argue that immunological studies in natural populations are pivotal to meeting this challenge: Many components of environmental change-shifts in biotic assemblages, altered climate patterns, and reduced environmental predictability-may affect host immunity. We suggest that wild ungulates can serve as model systems aiding the discovery of immunological mechanisms that link environmental change with parasite transmission dynamics. Our review of eco-immunological studies in wild ungulates reveals progress in understanding how co-infections affect immunity and parasite transmission; and how environmental and genetic factors interact to shape immunity. Changes in bioavailability of micronutrients have been linked to immunity and health in wild ungulates. Although physiological stress in response to environmental change has been assessed, downstream effects on immunity have not been studied. Moreover, the taxonomic range of ungulates studied is limited to bovids (bighorn sheep, Soay sheep, chamois, musk oxen, bison, African buffalo) and a few cervids (red deer, black-tailed deer). We discuss areas where future studies in ungulates could lead to significant contributions in understanding patterns of immunity and infection in natural populations and across species.

PLOS Neglected Tropical Diseases, Nov 11, 2022

Background Bovine tuberculosis (BTB) is a zoonotic disease of global importance endemic in Africa... more Background Bovine tuberculosis (BTB) is a zoonotic disease of global importance endemic in African buffalo (Syncerus caffer) in sub-Saharan Africa. Zoonotic tuberculosis is a disease of global importance, accounting for over 12,000 deaths annually. Cattle affected with BTB have been proposed as a model for the study of human tuberculosis, more closely resembling the localization and progression of lesions in controlled studies than murine models. If disease in African buffalo progresses similarly to experimentally infected cattle, they may serve as a model, both for human tuberculosis and cattle BTB, in a natural environment. Methodology/Principal findings We utilized a herd of African buffalo that were captured, fitted with radio collars, and tested for BTB twice annually during a 4-year-cohort study. At the end of the project, BTB positive buffalo were culled, and necropsies performed. Here we describe the pathologic progression of BTB over time in African buffalo, utilizing gross and histological methods. We found that BTB in buffalo follows a pattern of infection like that seen in experimental studies of cattle. BTB localizes to the lymph nodes of the respiratory tract first, beginning with the retropharyngeal and tracheobronchial lymph nodes, gradually increasing in lymph nodes affected over time. At 36 months, rate of spread to additional lymph nodes sharply increases. The lung lesions follow a similar pattern, progressing slowly, then accelerating their progression at 36 months post infection. Lastly, a genetic marker that correlated to risk of M. bovis infection in previous studies was marginally associated with BTB progression.

Frontiers in Microbiology, Feb 22, 2023

Extensive research in well-studied animal models underscores the importance of commensal gastroin... more Extensive research in well-studied animal models underscores the importance of commensal gastrointestinal (gut) microbes to animal physiology. Gut microbes have been shown to impact dietary digestion, mediate infection, and even modify behavior and cognition. Given the large physiological and pathophysiological contribution microbes provide their host, it is reasonable to assume that the vertebrate gut microbiome may also impact the fitness, health and ecology of wildlife. In accordance with this expectation, an increasing number of investigations have considered the role of the gut microbiome in wildlife ecology, health, and conservation. To help promote the development of this nascent field, we need to dissolve the technical barriers prohibitive to performing wildlife microbiome research. The present review discusses the 16S rRNA gene microbiome research landscape, clarifying best practices in microbiome data generation and analysis, with particular emphasis on unique situations that arise during wildlife investigations. Special consideration is given to topics relevant for microbiome wildlife research from sample collection to molecular techniques for data generation, to data analysis strategies. Our hope is that this article not only calls for greater integration of microbiome analyses into wildlife ecology and health studies but provides researchers with the technical framework needed to successfully conduct such investigations.

Rift Valley fever (RVF) is a mosquito-borne zoonotic viral disease native to the African continen... more Rift Valley fever (RVF) is a mosquito-borne zoonotic viral disease native to the African continent. Outbreaks tend to occur in the wet seasons, and can affect numerous mammalian species including African buffalo. It is debated how the virus survives the interepidemic period when it is not detected in mammalian populations, either in cryptic wildlife hosts or by vertical transmission in mosquito hosts. In chapters 1 and 2 of this dissertation I show that buffalo do become infected in the inter-epidemic period although that is not sufficient to maintain viral cycling in the system without additional mammalian hosts and high vertical transmission rates. Bovine tuberculosis is an emerging disease in sub-Saharan Africa, first detected in Kruger National Park buffalo populations in 1990. African buffalo are a maintenance host for BTB in the ecosystem, and there has been detailed research about pathogen provenance and diversity, effects on the host and transmission dynamics. These studies have focused on a single invasive pathogen, BTB-despite the fact that buffalo act as hosts for a multitude of pathogens. Fundamental theory in community ecology and immunology suggests that parasites within a host should interact, by sharing resources, competing for resources or by altering the immune response. In chapter 3 I show that animals with BTB are more likely to become infected with RVF, more likely to show clinical signs and that the presence of BTB increases the size of RVF epidemics in African buffalo. In chapters 4 and 5 I demonstrate that one of the mechanisms underlying this pattern may be immune-mediated whereby animals with BTB have altered susceptibility to RVF. Understanding how emerging diseases, like BTB, may affect native host-pathogen or pathogen-pathogen interactions will help us understand the full impact that emerging diseases may have on an ecosystem.

Scientific Reports, Apr 20, 2020

Studies in laboratory animals demonstrate important relationships between environment, host trait... more Studies in laboratory animals demonstrate important relationships between environment, host traits, and microbiome composition. However, host-microbiome relationships in natural systems are understudied. Here, we investigate metapopulation-scale microbiome variation in a wild mammalian host, the desert bighorn sheep (Ovis canadensis nelsoni). We sought to identify over-represented microbial clades and understand how landscape variables and host traits influence microbiome composition across the host metapopulation. To address these questions, we performed 16S sequencing on fecal DNA samples from thirty-nine bighorn sheep across seven loosely connected populations in the Mojave Desert and assessed relationships between microbiome composition, environmental variation, geographic distribution, and microsatellite-derived host population structure and heterozygosity. We first used a phylogenetically-informed algorithm to identify bacterial clades conserved across the metapopulation. Members of genus Ruminococcaceae, genus Lachnospiraceae, and family Christensenellaceae R7 group were among the clades over-represented across the metapopulation, consistent with their known roles as rumen symbionts in domestic livestock. Additionally, compositional variation among hosts correlated with individual-level geographic and genetic structure, and with population-level differences in genetic heterozygosity. This study identifies microbiome community variation across a mammalian metapopulation, potentially associated with genetic and geographic population structure. Our results imply that microbiome composition may diverge in accordance with landscape-scale environmental and host population characteristics.

Journal of Immunology, May 1, 2020

Diversity of MHC class I alleles within animal populations is necessary to prevent pathogen escap... more Diversity of MHC class I alleles within animal populations is necessary to prevent pathogen escape from adaptive immune responses. However, demonstrating this phenomenon is difficult especially in wild animal species where the effect of pathogen escape is more profound than in laboratory animal models. Desert bighorn sheep (Ovis canadensis nelsoni) are a charismatic megafauna native to the southwest of North America which are threatened by a number of infectious diseases and, more recently, paranasal tumors. We sought to develop a relatively inexpensive and rapid way to identify the diversity of MHC class I genes and alleles within individual bighorn sheep. Both DNA and RNA were isolated from leukocytes collected from 154 adult bighorn sheep from across different mountain ranges in Southern California. Previously identified primers from domestic sheep were used to amplify exons 2 and 3 from OMHC I genes while appending adapters for PacBio circular consensus sequencing. PCR amplicons from individual animals were then subjected to a second round of PCR to append index sequences to allow assigning of individual sequences to unique animals. We successfully identified over 40 unique MHC class I sequences expressed by bighorn sheep. Between 2 and 5 loci were amplified in each individual animal. Analysis of gDNA revealed several pseudogenes and other DNA sequences which were not transcribed. Finally, we demonstrate that particular DNA sequences are found within particular populations, suggesting that as bighorn populations fragment, there is a loss of MHC class I diversity.

bioRxiv (Cold Spring Harbor Laboratory), Dec 3, 2022

Infectious disease dynamics operate across biological scales: pathogens replicate within hosts, b... more Infectious disease dynamics operate across biological scales: pathogens replicate within hosts, but transmit among hosts and populations. Functional changes in the pathogen-host interaction thus generate cascading effects from molecular to landscape scales. We investigated within-host dynamics and among-host transmission of three strains of foot-and-mouth disease viruses (FMDVs) in their wildlife host, African buffalo. We combined data on viral dynamics and host immune responses with mathematical models to ask (i) How do viral and immune dynamics vary among FMDV strains? (SAT1, 2, 3); (ii) Which viral and immune parameters determine viral fitness within hosts?; and (iii) How do within-host dynamics relate to virus transmission among hosts? Our data reveal contrasting within-host dynamics among viral strains. However, SAT2 elicited more rapid and effective immune responses than SAT1 and SAT3. Within-host viral fitness was overwhelmingly determined by variation among hosts in immune response activation rates against FMDVs, but not by variation among individual hosts in viral growth rate. By contrast, our analyses investigating across-scale linkages indicate that viral replication rate in the host correlates with transmission rates among buffalo; and that adaptive immune activation rate determines the infectious period. Together, these parameters define the basic reproductive number, R 0 , of the virus, suggesting that viral invasion potential may be predictable from within-host dynamics. Future work should test the generality of these findings by including additional FMDV strains, and create a multi-scale model to link within-host and between-host dynamics explicitly.

bioRxiv (Cold Spring Harbor Laboratory), May 9, 2022

Feline upper respiratory tract disease (FURTD), often caused by infections etiologies, is a multi... more Feline upper respiratory tract disease (FURTD), often caused by infections etiologies, is a multifactorial syndrome affecting feline populations worldwide. Because of its highly transmissible nature, infectious FURTD is most prevalent anywhere cats are housed in groups such as animal shelters, and is associated with negative consequences such as decreasing adoption rates, intensifying care costs, and increasing euthanasia rates. Understanding the etiology and pathophysiology of FURTD is thus essential to best mitigate the negative consequences of this disease. Clinical signs of FURTD include acute respiratory disease, with a small fraction of cats developing chronic sequelae. It is thought that nasal mucosal microbiome changes play an active role in the development of acute clinical signs, but it remains unknown if the microbiome may play a role in the development and progression of chronic clinical disease. To address the knowledge gap surrounding how microbiomes link to chronic FURTD, we asked if microbial community structure of upper respiratory and gut microbiomes differed between cats with chronic FURTD signs and clinically normal cats. We selected 8 households with at least one cat exhibiting chronic clinical FURTD, and simultaneously collected samples from cohabitating clinically normal cats. Microbial community structure was assessed via 16S rDNA sequencing of both gut and nasal microbiome communities. Using a previously described ecophylogenetic method, we identified 37 and 27 microbial lineages within gut and nasal microbiomes respectively that significantly associated with presence of active FURTD clinical signs in cats with a history of chronic signs. Overall, we find that nasal and gut microbial communities may contribute to the development of chronic clinical course, but more research is needed to confirm our observations. .

Journal of Animal Ecology, Jan 27, 2023

Habitat fragmentation is an important driver of biodiversity loss and can be remediated through m... more Habitat fragmentation is an important driver of biodiversity loss and can be remediated through management actions aimed at maintenance of natural connectivity in metapopulations. Connectivity may protect populations from infectious diseases by preserving immunogenetic diversity and disease resistance. However, connectivity could exacerbate the risk of infectious disease spread across vulnerable populations. We tracked the spread of a novel strain of Mycoplasma ovipneumoniae in a metapopulation of desert bighorn sheep Ovis canadensis nelsoni in the Mojave Desert to investigate how variation in connectivity among populations influenced disease outcomes. M. ovipneumoniae was detected throughout the metapopulation, indicating that the relative isolation of many of these populations did not protect them from pathogen invasion. However, we show that connectivity among bighorn sheep populations was correlated with higher immunogenetic diversity, a protective immune response and lower disease prevalence. Variation in protective immunity predicted infection risk in individual bighorn sheep and was associated with heterozygosity at genetic loci linked to adaptive and innate immune signalling. Together, these findings may indicate that population connectivity maintains immunogenetic diversity in bighorn sheep populations in this system and has direct effects on immune responses in individual bighorn sheep and their susceptibility to infection by a deadly pathogen. Our study suggests that the genetic benefits of population connectivity could outweigh the risk of infectious disease spread and supports conservation management that maintains natural connectivity in metapopulations.

Cambridge University Press eBooks, Nov 14, 2019

Physiological and Biochemical Zoology