The epidemiology of soil-transmitted helminths in Bungoma, Kenya, with an emphasis on immuno-epidemiology in a community receiving anthelmintic treatment

Abstract

Soil-transmitted helminth (STH) infections are endemic in Kenya, where preventive anthelminthic treatment has been provided to school-age children annually, through a school-based deworming (SBD) programme, since 2012. The aim of this thesis was to investigate the epidemiology and immuno-epidemiology of STH infections in a whole community with an ongoing SBD programme to assess the impact of control on the prevalence and intensity of infection, plus the distribution of remaining infection in treated communities. This study was conducted in four rural villages near Bungoma, western Kenya. Samples were collected from 2,273 individuals between 2 and 93 years of age during two cross-sectional surveys in Mar-Apr and Aug-Sep 2014. Stool samples were analysed using Kato-Katz, blood samples were analysed using enzyme-linked immunosorbent assays (ELISA). 400mg albendazole was administered between the cross-sectional surveys to simulate a round of mass drug administration (MDA). At study baseline, Ascaris lumbricoides and Necator americanus infections had 9.8% and 6.7% prevalence, which were reduced to 1.8% and 1.4%, respectively, three months post-MDA. STH infection was highly aggregated in the population, and clustering at household and village levels was observed for A. lumbricoides infection. Young age and poor sanitation were risk factors for A. lumbricoides infection, while old age, farming, and poverty-associated factors increased the risk for N. americanus infection. The MDA had 93.9% coverage, 98.9% and 91.5% cure rates for A. lumbricoides and N. americanus, respectively, and was particularly effective in reducing hookworm infection in the older age groups of the population. A positive correlation was observed between hookworm age-prevalence and Necator-specific IgG4 antibody prevalence. No significant changes in seroprevalence were found post-treatment. There was evidence of cross-reactivity between antigens. This study highlights the need for improved control strategies and diagnostic tools for STH infections, particularly as SBD programmes bring us closer to the “endgame” of transmission elimination.