Aspergillus flavus infections in Galleria mellonella : a pathogen-host model system for the study of emerging diseases

To study emerging diseases, I employed a model pathogen-host system involving infections of insect larvae with the opportunistic fungus Aspergillus flavus, providing insight into three mechanisms ofpathogen evolution namely de novo mutation, genome decay, and virulence factoracquisition In Chapter 2 as a foundational experiment, A. flavus was serially propagated through insects to study the evolution of an opportunistic pathogen during repeated exposure to a single host. While A. flavus displayed de novo phenotypic alterations, namely decreased saprobic capacity, analysis of genotypic variation in Chapter 3 signified a host-imposed bottleneck on the pathogen population, emphasizing the host's role in shaping pathogen population structure. Described in Chapter 4, the serial passage scheme enabled the isolation of an A. flavus cysteine/methionine auxotroph with characteristics reminiscent of an obligate insect pathogen, suggesting that lost biosynthetic capacity may restrict host range based on nutrient availability and provide selection pressure for further evolution. As outlined in Chapter 6, cysteine/methionine auxotrophy had the pleiotrophic effect of increasing virulence factor production, affording the slow-growing auxotroph with a modified pathogenic strategy such that virulence was not reduced. Moreover in Chapter 7, transformation with a virulence factor from a facultative insect pathogen failed to increase virulence, demonstrating the necessity of an appropriate genetic background for virulence factor acquisition to instigate pathogen evolution.

Budding sprays and sketch of the life of General Sir Isaac Brock (1912)

A sketch of the life of General Sir Isaac Brock.

Perceptions of Technology and Manifestations of Language Learner Autonomy

a grounded theory study investigating perceptions of technology by learners of English as a second language

Moderating effects of gender and general self-efficacy on the relationship between sensation-seeking and adolescent substance use /

This study performed a aecondvy dau analysis of information collected during the Youth Leisure Study (YLS). The purpose of this study was to examine the potential moderating influences of gender and general self-efTicacy on the relationships aoKXig sensation-seeking and various forms of substance use in adolescents. Specifically, the predictive ability of sensation seeking on five adolescents substance use outcomes (alcohol, tobacco, and marijuana use; binge drinking; and number of times drunk) was examined. Moderated hierarchical multiple regression (MHMR) analyses were used to examine the relationships among study variables. The results for this study indicate that the relationships among sensation-seeking and forms of adolescent substance use are more complex than literature suggests. Main effect relationships were found consistently for sensation-seeking and general self-efficacy with each of the outcome variables. Results for gender were not consistent across the substance use outcomes. Gender was a significant predictor for marijuana use only. The moderating effects of general self-efficacy (GSE) on the sensation-seekingsubstance use relationship were inconsistent. While no significant interactions were found for tobacco or alcohol use outcomes, GSE was found to moderate the relationship between sensation-seeking and marijuana use indicating that feelings of high general selfefficacy act as a buffer or guard against marijuana use. A consistent pattern was found among the alcohol use variables (alcohol use. binge drinking, and number of times drunk). Gender was found to moderate each of these variables indicating that higher levels of sensation seeking are more predictive of higher levels of adolescent alcohol use in males only. Implications of this study on the field of education, are discussed further, and suggestions for future research are presented.

Transmission of West Nile virus in the Niagara Region among a population at risk for exposure

Background. West Nile Virus (WNV), a mosquito-borne flavivirus, is one of an increasing number of infectious diseases that have been emerging or re-emerging in the last two decades. Since the arrival ofWNV to Canada to present date, the Niagara Region has only reported 30 clinical cases, a small number compared to the hundreds reported in other regions of similar conditions. Moreover, the last reported human case in Niagara was in 2006. As it has been demonstrated that the majority of WNV infections are asymptomatic, the question remains whether the lack of clinical cases in Niagara truly reflects the lack of transmission to humans or if infections are still occurring but are mostly asymptomatic. Objectives. The general objective of this study was to establish whether or not active WNV transmission could be detected in a human population residing in Niagara for the 2007 transmission season. To fullfil this objective, a cross-sectional seroprevalence study was designed to investigate for the presence of anti-WNV antibodies in a sample of Mexican migrant agricultural workers employed in farms registered with the Seasonal Agricultural Workers Program (SAWP). Due to the Mexican origin of the study participants, three specific research objectives were proposed: a) determine the seroprevalence ofanti-WNV antibodies as well as anti-Dengue virus antibodies (a closely related virus prevalent in Mexico and likely to confound WNV serology); b) analyze risk factors associated with WNV and Dengue virus seropositivity; and c) assess the awareness of study participants about WNV infection as well as their understanding of the mode of transmission and clinical importance of the infection. Methodology: After obtaining ethics clearance from Brock University, farms were visited and workers invited to participate. Due to time constraints, only a small number of farms were enrolled with a resulting convenience and non-randomized study sample. Workers' demographic and epidemiological data were collected using a standardized questionnaire and blood samples were drawn to determine serum anti-WNV and anti- Dengue antibodies with a commercial ELISA. All positive samples were sent to the National Microbiology Laboratory in Winnipeg, Manitoba for confirmation with the Plaque Reduction Neutralization Test (PRNT). Data was analyzed with Stata 10.0. Antibody determinations were reported as seroprevalence proportions for both WNV and Dengue. Logistic regression was used to analyze risk factors that may be associated with seropositivity and awareness was reported as a proportion of the number of individuals possessing awareness over the total number of participants. Results and Discussion. In total 92 participants working in 5 farms completed the study. Using the commercial ELISA, seropositivity was as follows: 2.2% for WNV IgM, 20.7% for WNV IgG, and 17.1 % for Dengue IgG. Possible cross-reactivity was demonstrated in 15/20 (75.0%) samples that were positive for both WNV IgG and Dengue IgG. Confirmatory testing with the PRNT demonstrated that none of the WNV ELISA positive samples had antibodies to WNV but 13 samples tested positive for anti-Dengue antibodies (14.1 % Dengue sereoprevalence). The findings showed that the ELISA performance was very poor for assessing anti-WNV antibodies in individuals previously exposed to Dengue virus. However, the ELISA had better sensitivity and specificity for assessing anti-Dengue antibodies. Whereas statistical analysis could not be done for WNV seropositivity, as all samples were PRNT negative, logistic regression demonstrated several risk factors for Dengue exposure_ The first year coming to Canada appeared to be significantly associated with increased exposure to Dengue while lower socio-economic housing and the presence of a water basin in the yard in Mexico appeared to be significantly associated with a decreased exposure to Dengue_ These seemingly contradictory results illustrate that in mobile populations such as migrant workers, risk factors for exposure to Dengue are not easily identified and more research is needed. Assessing the awareness of WNV and its clinical importance showed that only 23% of participants had some knowledge of WNV, of which 76% knew that the infection was mosquito-borne and 47% recognized fever as a symptom. The identified lack of understanding and awareness was not surprising since WNV is not a visible disease in Mexico. Since WNV persists in an enzootic cycle in Niagara and the occurrence of future outbreaks is unpredictable, the agricultural workers remain at risk for transmission. Therefore it important they receive sufficient health education regarding WNV before leaving Mexico and during their stay in Canada. Conclusions. Human transmission of WNV could not be proven among the study participants even when due to their occupation they are at high risk for mosquito bites. The limitations of the study sample do not permit generalizable conclusions, however, the study findings are consistent with the absence of clinical cases in the Niagara Region, so it is likely that human transmission is indeed neglible or absent. As evidenced by our WNV serology results, PRNT must be utilized as a confirmatory test since false positivity occurs frequently. This is especially true when previous exposure to Dengue virus is likely.

Profile Portrait of Major General Sir Isaac Brock 1769-1812

This work is a copy of a pastel oval portrait of General Brock that is supposedly the only known portrait of Brock to be done in his lifetime. The original was by William Berczy, circa 1808, and is in the possession of Captain M.H.T Mellish, a descendant of one of Brock's sisters. This portrait was completed on canvas.

Cellular Mechanisms of Resveratrol's Interaction with Mitochondrial Reactive Oxygen Species Metabolism

Resveratrol, a polyphenol found naturally in red wines, has attracted great interest in both the scientific community and the general public for its reported ability to protect against many of the diseases facing Western society today. While the purported health effects of resveratrol are well characterized, details of the cellular mechanisms that give rise to these observations are unclear. Here, the mitochondrial antioxidant enzyme Mn superoxide dismutase (MnSOD) was identified as a proximal target of resveratrol in vitro and in vivo. MnSOD protein and activity levels increase significantly in cultured cells treated with resveratrol, and in the brain tissue of mice given resveratrol in a high fat diet. Preventing the increase in MnSOD levels eliminates two of resveratrol’s more interesting effects in the context of human health: inhibition of proliferative cell growth and cytoprotection. Thus, the induction of MnSOD is a critical step in the molecular mechanism of resveratrol. Mitochondrial morphology is a malleable property that is capable of impeding cell cycle progression and conferring resistance against stress induced cell death. Using confocal microscopy and a novel ‘cell free’ fusion assay it was determined that concurrent with changes in MnSOD protein levels, resveratrol treatment leads to a more fused mitochondrial reticulum. This observation may be important to resveratrol’s ability to slow proliferative cell growth and confer cytoprotection. Resveratrol's biological activities, including the ability to increase MnSOD levels, are strikingly similar to what is observed with estrogen treatment. Resveratrol fails to increase MnSOD levels, slow proliferative cell growth and confer cytoprotection in the presence of an estrogen receptor antagonist. Resveratrol's effects can be replicated with the specific estrogen receptor beta agonist diarylpropionitrile, and are absent in myoblasts lacking estrogen receptor beta. Four compounds that are structurally similar to resveratrol and seven phytoestrogens predicted to bind to estrogen receptor beta were screened for their effects on MnSOD, proliferative growth rates and stress resistance in cultured mammalian cells. Several of these compounds were able to mimic the effects of resveratrol on MnSOD levels, proliferative cell growth and stress resistance in vitro. Thus, I hypothesize that resveratrol interacts with estrogen receptor beta to induce the upregulation of MnSOD, which in turn affects cell cycle progression and stress resistance. These results have important implications for the understanding of RES’s biological activities and potential applications to human health.