Date of Award

January 2013

Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Alison Galvani

Abstract

Background: Chronic hookworm infection affects an estimated 576 to 740 million people worldwide. Despite mass drug administration efforts, the morbidity associated with this soil-transmitted helminth remains a significant public health issue. Due to inter- and intra- community heterogeneity in susceptibility to infection, mathematical modeling can serve as an effective and efficient tool for investigating hookworm transmission in different settings and for guiding policymakers to consider new treatment and prevention strategies.

Methods: Here we developed an age-structured, compartmental S-I model to identify epidemiological parameters for hookworm infection and to assess rates of attributable anemia within the population of Zanzibar. The model was first used to address the relative contributions of age group (adults versus children) and infection intensity status (high versus low) in transmission. The Markov chain Monte Carlo (MCMC) method was implemented to generate negative binomial distribution parameters for describing population-level parasite aggregation. Gibbs sampling and data on prevalence of hookworm infection were used in a subsequent MCMC to parameterize the overall model and account for uncertainty. Maximum likelihood point estimates for force of infection and natural recovery were derived from the 10,000 posterior distributions generated. Empirical data on average hemoglobin levels for given fecal egg count categories were included in the analysis to give distributions for the relative risk of moderate-to-severe anemia (hemoglobin < 90 g/L) among infected versus susceptible individuals.

Results: Using maximum likelihood estimates for the negative binomial distribution parameters, it was determined that children prone to high intensity hookworm infections were 4.9 times as infectious as children prone to lower intensity infection; high intensity infection adults were considered to be 4.7 times as infectious as low intensity infection adults. Model predictions with and without uncertainty were consistent in estimating that approximately 10% of the infected child population experienced moderate-to-severe anemia attributable to hookworm infection.

Conclusion: The present model provides a population-level compartmental model framework for assessing hookworm-attributable morbidity independent of assumptions about worm burden thresholds. To evaluate the effectiveness of different intervention strategies at reducing the incidence of infection and rates of hookworm-attributable anemia, the current epidemiological model can be extended structurally to include treatment and vaccine parameters.

Comments

This is an Open Access Thesis.

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