Browsing by Author "Nunn, Charles"

Background: Approximately 3.8 million people die annually from illnesses caused by household air pollution (HAP). Cooking related HAP is the second leading cause of disease in Madagascar. Our exploratory study aims to examine the effect of cooking fuel smoke exposure on lung function and respiratory symptoms.Methods: A cross-sectional study was conducted in Mandena, Madagascar from 2016 through 2018. Adults aged ≥18 years completed a survey on respiratory symptoms and cooking habits and performed spirometry for FEV1 and FEV6 values. Results: Of the 140 participants, 95 individuals were included in the multiple regression model. Being the primary cooks was significantly associated with decreasing FEV1 (-0.30; 95% CI: -0.57, -0.04) and FEV6 (-0.32, 95% CI: -0.57,-0.06). Cooking indoors significantly decreases FEV6 compared to cooking outdoors (-0.26, 95% CI: -0.50,-0.03). Conclusion: Reduced lung function and increased respiratory disease are most common among primary cooks. Reduced lung function was associated with cooking indoors. Further studies are essential to investigate HAP’s effect on Madagascar communities.

The skin is home to trillions of microbes, many of which are recently implicated in immune system regulation and various health conditions (33). The skin is continuously exposed to the outside environment, inviting microbial transfer between human skin and the people, animals, and surfaces with which an individual comes into contact. Thus, the aim of this study is to assess how different environmental exposures influence skin microbe communities, as this can strengthen our understanding of how microbial variation relates to health outcomes. This study investigated the skin microbial communities of humans and domesticated cattle living in rural Madagascar. The V3 region of the 16S rRNA gene was sequenced from samples of zebu (the domesticated cattle of Madagascar), zebu owners, and non-zebu owners. Overall, human armpits were the least diverse sample site, while ankles were the most diverse. The diversity of zebu samples was significantly different from armpits, irrespective of zebu ownership (one-way ANOVA and Tukey’s HSD, p<0.05). However, zebu owner samples (from the armpit, ankle forearm, and hand) were more similar to other zebu owner samples than they were to zebu, yet no more similar to other zebu owner samples than they were to non-zebu owner samples (unweighted UniFrac distances, p<0.05). These data suggest a lack of a microbial signature shared by zebu owners and zebu, though further taxonomic analysis is required to explain the role of additional environmental variables in dictating the microbial communities of various samples sites. Understanding the magnitude and directionality of microbial sharing has implications for a breadth of microbe-related health outcomes, with the potential to explain mosquito host preference and mitigate the threats of vector-borne diseases.

Primates span incredible behavioral and ecological diversity, and this diversity is reflected in the shape of the skull. This dissertation asks two questions surrounding the evolution of primate skull shape: 1) what are the macroevolutionary correlates of primate skull shape? And 2) what is the pattern of phenotypic integration in the primate skull at a macroevolutionary scale? To address these questions, I compiled a broad comparative dataset of anatomical landmarks identified from 3D scans of primate skulls and analyzed this data using statistical methods that combine geometric morphometrics and phylogenetic comparative methods. To investigate the macroevolutionary correlates of skull shape, I used multivariate phylogenetic generalized linear models to test for relationships between skull shape and several variables that are predicted to be correlated with skull shape: allometry, typical diet, tree gouging behavior, activity pattern, and sexual dimorphism. I found strong phylogenetic signal for primate skull shape, confirming the need for phylogenetic comparative methods. Allometry was a significant predictor of skull shape, with larger primates having relatively small, convergent orbits, and anteroposteriorly short skulls compared to small primates. Sexual dimorphism was associated with a dramatically lengthened rostrum, probably to facilitate a large gape in aggressive displays. Folivory was associated with deeper mandibles, which may improve mechanical advantage and strain resistance. To investigate patterns of phenotypic integration in the skull, I performed hierarchical clustering analyses on phylogenetically corrected inter-landmark covariance matrices. In contrast to previous research, I did not find evidence for distinct phenotypic modules in the primate skull, and I argue that this discrepancy is due to methodological shortcomings of past research that biased results towards identifying different anatomical regions as discrete modules. This dissertation represents one of the first investigations of primate skull shape at a macroevolutionary scale, and demonstrates that the combination of geometric morphometrics and phylogenetic comparative methods can yield novel insights into evolutionary morphology.

Human disturbance of wildlife habitat leads to a change in wildlife community composition of an area, often decreasing species richness and favoring opportunistic or generalist species that thrive in a wide variety of environmental conditions. Such changes in a community have the potential to alter disease transmission dynamics and can affect human health. To make progress in linking ecosystem changes and disease risk, it is essential to develop new techniques to evaluate how wildlife communities interact, and how ecosystem stressors affect disease risk. The construction of social networks based on spatial data will provide information on community structure and disease transmission dynamics in relation to anthropogenic land use change. In the summer of 2017, small mammals were captured for 5 consecutive days at three sites in northeast Madagascar. Spatial data, Leptospira infection status, and morphometric data were collected from small mammals to identify host characteristics important to disease transmission. Data were input into R to construct a spatial network that aimed to model disease transmission. Through this study I found that a spatial network does not adequately model the environmental transmission of Leptospira, and highlights the importance of considering pathogen life cycle during the construction of disease transmission models. Additionally, Mus musculus were found to connect separate communities of small mammals, and thus inhabit an epidemiologically critical position in the spatial network.

Parasitism is integral to primate evolution, contributing to major life history tradeoffs with other processes critical to reproductive success and survival. I investigate how infection with the tapeworm Taenia serialis affects geladas (Theropithecus gelada) in the Simien Mountains National Park, Ethiopia. After identifying T. serialis as the parasite behind the protuberant cysts regularly observed in geladas with the use of molecular tools, I described an overall cyst prevalence of 4.8% in the study population (Chapter 2). To identify infections that do not present as visible cysts, I adapted a non-invasive monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) to detect circulating Taenia spp. antigen in gelada urine (Chapter 4). This assay detected Taenia antigen with high accuracy (98.4% specificity, 98.5% sensitivity, and an AUC (area under the curve) of 0.99). Implementing this assay in the study population, I found that infection is substantially more widespread than would be predicted based on the occurrence of visible T. serialis cysts (16.5% of individuals of unknown status tested positive for antigen presence at least once). Contrary to the female-bias observed in many Taenia-host systems, I found no significant sex bias in either cyst presence or antigen presence. Age, on the other hand, predicted cyst presence (older individuals were more likely to show cysts) but not antigen presence (Chapter 3). This indicates that T. serialis may infect individuals early in life but result in visible disease only later in life. I found that cysts were strongly associated with decreased survival and reproductive success in adult geladas (Chapter 4). Counter to expectations, T. serialis cysts were not strongly associated with decreased fecal testosterone metabolite concentrations (Chapter 5). This suggests that the mechanisms underlying the wild T. serialis-gelada relationship differ from those observed in experimental systems. Together, the analyses contained in this dissertation offer novel insights into the predictors, costs, and consequences of a trophically transmitted larval parasite in wild primates.

Introduction: Hypertension, the primary risk factor for the leading cause of mortality, cardiovascular diseases, is increasing in all parts of the world, including low-income countries. This thesis explores the prevalence and predictors of elevated blood pressure in rural farmers in northeastern Madagascar. The prevalence of hypertensive blood pressure was compared as defined by two commonly used hypertension standards, the World Health Organization (WHO), and the American College of Cardiology & the American Heart Association (ACC/AHA). The hypothesized drivers of systolic and diastolic blood pressure were investigated, focusing specifically on age, gender, body mass index (BMI), salt intake, and stress. Methods: Over 1,200 surveys were conducted from 2019 to 2022 in four villages in the Sava Region of Madagascar, where blood pressure readings were obtained on each participant. A subset of the sample in the last field season, participated in additional questions related to salt consumption and a measurement of salt taken over the course of seven days. A subsample of forty-eight participants completed an additional survey regarding stress. Generalized linear mixed models were run to assess associations involving blood pressure, salt intake and stress, and other predictions involving age, gender, and BMI. Results: The different standards of hypertension, as defined by the WHO and the ACC/AHA, changed the respective prevalence of elevated blood pressure for this population markedly, nearly doubling the prevalence of hypertension if the more stringent American standard was used (WHO=29.7%, ACC/AHA=59.6%). Age was found to be a strong predictor of blood pressure as well as BMI, while salt intake, stress, and gender had weaker associations. Conclusion: The prevalence of elevated blood pressure in this population was markedly higher than that found in other studies conducted in this region and globally. Findings regarding lifestyle factors, salt intake and stress, as individual drivers of blood pressure were found to be inconclusive. Further research should be performed in this population to determine the predictors and lifestyle factors associated with blood pressure and the extent of their influence in this region. Consideration for standards of practice and diagnosis should be carefully considered in this population, as the burden of hypertension would potentially increase with a change in practice standard.

As deforestation occurs, the contact between humans and wildlife is expected to increase, resulting in increased risk of disease spillover to humans. Landscape modification and other spatio-temporal variables will influence population dynamics of small mammals, directly influencing the risk and transmission of zoonotic disease between species and humans. The study aimed to assess the influence of spatio-temporal variables on the trapping of small mammals across habitats of varying disturbance in the SAVA Region of Madagascar. Additionally, the study assessed the distribution patterns of small mammals within habitats, as well as the species diversity across habitats and throughout seasons. Endemic and invasive small mammals were trapped in 100m x 100m grids and two 100m pitfall lines over six consecutive days, in rice fields, sugar cane fields, vanilla fields, savoka, primary forest and secondary forest. The findings of the study suggest that heavily disturbed habitats are associated with capturing invasive species, exhibit low species diversity, and instances of aggregation during the ‘end of dry’ and ‘dry’ seasons. Considering the findings, highly disturbed habitats, like agricultural habitats, have a higher risk of disease than the risk in less disturbed habitats. Thus, the risk of disease spillover to humans is likely to be higher in these more disturbed habitats.

Because water is essential for life, when it is scarce, it may be one of the most important drivers of animal behavior. Despite its clear importance, water is relatively poorly studied in terms of its impact on primate behavior, and previous research has been limited to observational studies. This dissertation takes a combined experimental and observational approach to study behavior related to water acquisition in captive and wild lemurs. Specifically, I investigated how several dimensions of water sources influence lemur behavior, including their parasite transmission risk, spatial distribution, and predation risk. In experiments, I manipulated the fecal contamination of water with several species of lemurs in captivity at the Duke Lemur Center, and found that lemurs strongly preferred clean to feces-contaminated water in captivity (Chapter 2). I expanded this initial study to a more comprehensive examination of the impact of water scarcity on the behavior of wild red-fronted lemurs (Eulemur rufifrons) in Kirindy Forest, Madagascar. This wild study population requires drinking water to survive, but water is extremely limited during the dry season. I experimentally manipulated water availability in the habitat by introducing artificial water sources, and I tracked how changes to the distribution of water influenced the ranging patterns of the lemurs recorded by GPS collars. Lemur groups shifted the intensity of their habitat use relative to natural and experimental water availability (Chapter 3). Using a similar experimental approach to the study in captivity, I determined that wild, water-limited lemurs also preferred to drink clean water. Based on lemur groups’ selection of natural water sources as measured with camera traps, wild lemurs also selected water sources with lower fecal contamination more frequently, but with some constraints. Lemurs were more likely to return to waterholes and returned to them after shorter time intervals when they had lower levels of fecal contamination in the areas around them. However, lemurs’ natural waterhole choices reflected that fecal contamination was a secondary factor determining water source selection, behind travel distance (Chapter 4). Finally, I examined how predation risk, i.e. the presence of fossa (Cryptoprocta ferox) and Madagascar harrier hawks (Polyboroides radiatus), influenced red-fronted lemurs’ spatiotemporal patterns of waterhole use. Red-fronted lemurs used waterholes at times of day when predators were least likely to be present (Chapter 5). This study, with its combined experimental and observational approach, identifies water as an important factor that shapes wild primate behavior. I found that lemurs were flexible in their responses to changes in water distribution, parasite risk, and predation risk. I suggest that water should be the focus of future behavioral research in primates, especially given the relevance of water for human evolution and the potential for climate change and human land use to further alter water availability.