Date of Award

Summer 2022

Document Type

Open Access Dissertation

Department

Epidemiology and Biostatistics

First Advisor

Melissa Nolan

Abstract

The main objectives of this dissertation were to investigate the seroprevalence of Spotted Fever Group Rickettsioses (SFGR) antibodies in a specific vulnerable population at high risk for vector-borne disease in El Salvador, understand the relevant risk factors for SFGR past and acute infection in this same population through logistic regression modeling, and clarify the presence of SFGR bacteria in locally collected ticks.

SFGR are a group of bacterial diseases caused by species in the Rickettsia genus of the phylogenetic spotted fever group. These are tick-borne diseases (TBD) that have been described in almost every region of the world. SFGR are categorized as neglected bacterial pathogens due to a lack of tools for definitive diagnoses, their underreported nature, and their tendency to impact marginalized populations and those in poverty more seriously.

Our previous 2018 study examined the prevalence of Chagas disease and gastrointestinal (GI) parasites among a cohort of children in the Department of Sonsonate, El Salvador. Banked human sera samples from this study were used for understanding seroprevalence of antibodies to SFGR bacteria through two antibody assays, the focus of Chapter 4. Our results found an overall immunoglobulin G (IgG) antibody prevalence (representing past infection) of 2.5% and an immunoglobulin M (IgM) antibody prevalence (representing acute infection) of 10.7%. Previous Chagas disease positive status was associated with SFGR antibody prevalence, and a hotspot of antibody positive and equivocal results was identified. Chapter 5 provided a more in-depth picture of SFGR risk through examination the association of environmental risk factors and antibody positive status. We found enrollment in the wet season, increased age, male sex, increased maternal education, and previous household infection increased odds of SFGR antibodies. Finally, Chapter 6 investigated the presence of SFGR bacteria in collected ticks from El Salvador. Traditional and quantitative polymerase chain reaction (PCR) yielded multiple pathogenic bacteria including SFGR pathogens in up to 48.8% of ticks. Multiple ticks were simultaneously infected with more than one pathogenic bacterial species.

These findings provide crucial information regarding the presence of pathogenic SFGR bacteria circulating in the environment in El Salvador. This is the first report of these bacteria in the country. Additionally, identified risk factors of antibody presence in this vulnerable population of children adds to the small body of research regarding human risk to SFGR in Central America. Future research should aim to measure antibody presence in populations in adults as well as children to increase generalizability, encompass a larger geographical area of El Salvador, and study the relationships between infected animals, ticks, and humans for a more holistic epidemiologic frame of reference.

Available for download on Thursday, October 05, 2023

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