No description available.

Soil-transmitted helminth (STH) (A. lumbricoides, T. trichiura and hookworm) infections are a significant public health concern in Honduras. These infections are treatable using inexpensive anthelmintic medications, however long-term control and eradication will require large investments in public and private sanitation infrastructure. Importantly, both types of interventions are targeted towards high-risk populations and regions rather than individuals. The goal of this thesis is to contribute to improving the efficiency of soil-transmitted helminth control efforts in Honduras. In our first study, we use multiple regression analyses to identify determinants of STH infections and generate estimates of A. lumbricoides, T. trichiura and hookworm infection prevalence, as well as recommended deworming frequencies, for each of Honduras’ 298 municipalities. Our estimates suggest that prevalence of all three infections has declined over time, however 75% of municipalities still require annual or semi-annual deworming. In our second study, we quantify how the type of region used for measuring prevalence and allocating resources can impact the success and efficiency of public health programs. More specifically, we compare administrative regions to alternative zoning schemes at the same geographic scale. Our findings suggest that regions designed to be homogeneous with respect to prevalence can be more efficient than existing municipalities (at the same scale) for distributing resources. This research has implications on future control efforts. / Thesis / Master of Science (MSc)

Transmissible spongiform encephalopathies (TSEs) or prion diseases, are subacute neurodegenerative diseases that infect humans and animals. Many of these diseases are acquired by peripheral exposure (e.g. orally). After oral exposure prion replication within the Peyer's patches (PP) in the small intestine is necessary for the efficient spread of the disease to the brain. Within the intestine, bacteria and pathogenic microorganisms can affect the status of the gut associated lymphoid tissue (GALT). GALT consists of PP and isolated lymphoid follicles (ILF) that maintain homeostasis and protect from infections. Therefore, factors which modify GALT status, might dramatically affect oral prion disease pathogenesis by influencing the uptake of prions from the gut lumen or expanding their distribution within the host. Chronic intestinal helminth infections are common in animals and in man, and can cause significant pathology within the intestine. Little is known of the effects that intestinal helminth infections may have on oral prion diseases susceptibility. Therefore, in this study the influence that co-infection with Heligmosomoides polygyrus (a natural pathogen of the mouse small intestine) may have on oral prion disease pathogenesis and susceptibility was determined. The studies consisted of groups of 4 (for H. polygyrus characterization and for early prion detection) and 8 (for H. polygyrus-prion co-infection to terminal stage) mice infected with H. polygyrus (orally) alone or subsequently infected with ME7 scrapie prions (orally) at different time-points after parasitic infection. The effects of the H. polygyrus infection alone, and on oral prion disease pathogenesis and susceptibility were then determined. Initially the characterization of H. polygyrus infection on the host intestine revealed that this parasite caused significant pathology in the small intestine and affected the GALT microarchitecture. In the PP follicles, H. polygyrus infection increased the area of follicular dendritic cell expression, altered the positioning of mononuclear phagocytes and increased M cell density. H. polygyrus infection also reduced the number of ILF in both the small and large intestines. Additional studies in mice co-infected with a low dose of prions, revealed that these pathological changes affected the survival time and disease susceptibility. Data also show that the extent of the effects on prion disease pathogenesis and susceptibility were dependent on the stage of the helminth infection at which the mice were orally-exposed to prions. Data demonstrate that co-infection with the gastrointestinal helminth H. polygyrus can influence oral prion disease pathogenesis and susceptibility. Helminth infections can significantly modify the microarchitecture of the gut and the GALT. Data presented suggest the pathological changes that pathogens such as small intestinal helminths cause, may also influence the uptake of prions from the gut lumen after oral exposure.