The Hygiene Hypothesis and Old Friends Hypothesis focus attention on the coevolutionary relationship between humans and pathogens, positing that reduced pathogen exposure in economically developed nations is responsible for immune dysregulation and associated increases in chronic inflammation, allergy, and autoimmunity. Despite progress in testing these ideas, few studies have examined these relationships among populations undergoing the transition from traditional to more market-based lifestyles. The present study tests relationships between economic development and social change, altered infectious disease exposure, and immune function among the Shuar forager-horticulturalists of Amazonian Ecuador, a population undergoing rapid economic change associated with increased market participation. Using stool samples to assess soil-transmitted helminth (STHs; parasitic intestinal worms) burden, dried blood spot measurement of the inflammatory marker C-reactive protein (CRP), and interviews to evaluate level of market integration (MI; the suite of social and cultural changes associated with rapid economic development) and disgust sensitivity, this dissertation tests the Hygiene and Old Friends Hypotheses. The first study tests relationships between STH exposure and MI, using geographic location in relation to the regional market center as a proxy for MI. This study documents lower rates of STHs in people living in more market integrated regions. The second study tests the coevolutionary role that STHs and other pathogens have played in shaping human psychology and behavior. Findings suggest that pathogen exposure has acted as a selective pressure, resulting in evolved disgust sensitivity toward pathogen related stimuli. This study provides evidence that disgust sensitivity is calibrated to local environments, acting to decrease STH exposure. The third study tests the role of STHs in immune function. CRP was positively related to age in uninfected individuals. No relationships existed for more traditionally living or infected individuals. These findings suggest that STH exposure may decrease the risk of developing chronic inflammation and associated diseases with advancing age. These studies provide support for the idea that STHs provide stimuli that decrease chronic inflammation, suggesting that altered intestinal microflora in developed nations may be partially responsible for the development of chronic inflammatory disorders like allergy and autoimmunity. This dissertation includes previously published and unpublished coauthored material.

The aim of this study was to examine whether three different psychological predictors; Health anxiety (SHAI), Disgust sensitivity (DS-R) and intolerance of uncertainty (IUS-12) could predict COVID-19-related anxiety in students at Orebro University, Sweden. It was hypothesized that there would be a significant relationship between the three psychological behaviors and pandemic-related anxiety. An online survey, consisting of both standardized and non-standardized questionnaires, was constructed. The survey was completed by 199 participants, aged between 19-48 (M = 25.14 and SD = 5.35) from Orebro University, Sweden through Limesurvey. A correlation revealed that Health anxiety and Disgust sensitivity were significantly correlated with COVID-19-related anxiety. The regression analysis revealed that there was a significance between the three psychological behaviors and COVID-19-related anxiety. In conclusion, Health anxiety, Disgust sensitivity and intolerance of uncertainty, could indeed be associated with COVID-19-related anxiety in the students. / Syftet med studien är att examinera huruvida tre olika psykologiska beteenden; Health anxiety (SHAI), Disgust sensitivity (DS-R) och Intolerance of uncertainty (IUS-12) kan förutse COVID-19-relaterad ångest i studenter på Örebro Universitet. Det hypotiserades att det skulle finnas en signifikant relation baserat på tidigare studier. En online enkät, med både standardiserade och icke-standardiserade frågeformulär, konstruerades. Antal deltagare som kompletterade enkäten genom Limesurvey var 199 studenter mellan åldrarna 19–48 (M = 25.14 och SD = 5.35) från Örebro Universitet. Genom en korrelationsanalys kunde man se att både Health anxiety och Disgust sensitivity var signifikant korrelerade med COVID-19-relaterad Pandemi. Avslutningsvis, en multipel regressionsanalys visade att Health anxiety, Disgust sensitivity och Intolerance of uncertainty var signifikant relaterat med COVID-19-relaterad ångest i studenterna.

This paper tests Reiss' (1991) expectancy theory of fearfulness. Reiss' moderation model of fears speculates that individual differences in fearfulness and phobic avoidance is a function of the interaction between trait vulnerabilities (i.e., sensitivities) and beliefs about potential outcomes during exposure to phobic stimuli (i.e., expectancies). Four hundred and forty-five undergraduates completed questionnaires related to Reiss' fundamental sensitivities (e.g., "anxiety sensitivity"), expectancies (e.g., "expectancy of physical injury or harm") and the intensity of common fears. Informed by findings concerning fear-related outcome expectancies, a system for measuring expectancies was developed for this study called the Focus of Apprehension Survey Schedule (FASS). Additionally, "disgust sensitivity" and "expectancy of contamination or illness" were included to examine whether they account for fearfulness beyond that predicted by Reiss' sensitivities and expectancies alone. In Experiment 1, hierarchical multivariate regression was employed to test Reiss' moderation model of expectancy theory for four fear subtypes (animal, blood/injection/injury (BII), claustrophobic, social). For each of these fear types, results did not support Reiss' moderation model. However, disgust sensitivity improved the prediction of animal fears and contamination expectancies improved the prediction of BII fears beyond Reiss' fundamental sensitivities and expectancies alone. In Experiment 2, a competing mediation model of expectancy theory was tested in which sensitivities were expected to indirectly influence individual differences in fearfulness through outcome expectancies. Results of path analysis using LISREL 8.54 did not support a mediation model per se. However, expectancies were found to mediate relationships between sensitivities and fears in several predicted instances (e.g., contamination expectancies mediated the disgust-BII fears relationship). The results provide some encouraging replications of prior studies and are discussed in the context of implications for theories of fear as well as for future directions in research.

The emotion of disgust is understudied. It has been implicated in various forms of psychopathology, but its overall influence remains unclear. New and improved methods and constructs are required if we are to better understand the relationship of disgust in attitude formation and psychological functioning. This study was an investigation of a measure referred to herein as the Disgust Propensity and Sensitivity Evolutionary Scale (DPSES). A total of 655 participants were recruited from a private university in the southeastern United States to complete a pencil -and-paper version of the measure in exchange for course credit. Exploratory factor analysis revealed an adequate five-factor structure that was further evaluated and supported through confirmatory factor analysis. The five-factor structure of the DPSES was determined to assess properties of disgust propensity, disgust sensitivity, sexual, moral, and pathogen disgust. Women's scores were significantly higher than males' across all subscales (Cohen's d = 0.59 for disgust propensity, d = 0.62 for disgust sensitivity, d = 1.73 for sexual disgust, d = 0.37 for moral disgust, and d = 0.70 for pathogen disgust). Women are repeatedly demonstrated to have stronger reactions to disgust than men, most particularly in relation to sexual associations. A better overall understanding of reactions, gender differences, and ways that maladaptive responses to disgust influence various psychological disorders and dysfunctions increases the potential for advancements in corresponding diagnostic and treatment strategies.