Abstract
BackgroundThe scientific community has recently summarized the desired characteristics for diagnostic tools across the different phases of a soil-transmitted helminth (STH) mass drug administration (MDA) program. Although serology meets some of the desired criteria, there is a scarcity of data on baseline serological profiles in human populations, both prior to and during MDA programs.MethodsIn this study, we compared the copromicroscopic and the serological infection profiles in 600 school-aged children (SAC) and 600 adults at the advent of the MDA program in Jimma Town, Ethiopia. The serological profiles were examined by two ELISAs that measure IgG4 responses to the Ascaris suum haemoglobin antigen (AsHb) and a somatic extract of lung stage larvae (AsLungL3). Three years into the MDA program, we sampled another group of 600 SAC from the same schools to assess the reduction in prevalence and intensity of Ascaris infections measured by copromicroscopy and serology.Principal findingsPrior to the start of MDA, copromicroscopy revealed an Ascaris prevalence of 31.0% and a mean fecal egg count of 2,919 eggs per gram (EPG) in SAC. Following three years of biannual treatment, the prevalence reduced to 13.2% (57.8% reduction) and the mean fecal egg count to 1,513 EPG (48.1% reduction). This reduction was also reflected in the serological results. The seroprevalence reduced with 40.9% and 27.4% and the mean optical density ratio reduced with 44.2% and 38.2% as measured by the AsHb or AsLungL3 ELISA respectively. We also showed that, despite a decreasing coproprevalence, seroprevalence to Ascaris increased with age.ConclusionsThis study is the first to provide IgG4 response profiles of an endemic population to two different A. suum antigens. The results suggest that exposure to the infectious stages of Ascaris reaches beyond SAC alone. Furthermore, it highlights the possible use of serological assays to monitor changes in STH exposure during MDA programs.
Highlights
In 2012, more than 70 pharmaceutical companies, governments, and global health organizations signed the London Declaration on Neglected Tropical Diseases (NTDs) and committed themselves to control and eliminate NTDs at the individual patient level or at the population level through programs of mass drug administration (MDA)
The results suggest that exposure to the infectious stages of Ascaris reaches beyond school-aged children (SAC) alone
It highlights the possible use of serological assays to monitor changes in soil-transmitted helminth (STH) exposure during MDA programs
Summary
In 2012, more than 70 pharmaceutical companies, governments, and global health organizations signed the London Declaration on Neglected Tropical Diseases (NTDs) and committed themselves to control and eliminate NTDs at the individual patient level or at the population level through programs of mass drug administration (MDA). Soil-transmitted helminthiasis is caused by a group of intestinal worms (Ascaris lumbricoides, Trichuris trichiura and two hookworm species (Ancylostoma duodenale and Necator americanus)) and is considered one of the most important NTDs that is amenable to control through MDA. Copromicroscopy lacks the performance to make well-founded decisions when a program reaches its endgame [10, 11]. The scientific community has recently summarized the desired characteristics for diagnostic tools across the different phases of a soil-transmitted helminth (STH) mass drug administration (MDA) program. Serology meets some of the desired criteria, there is a scarcity of data on baseline serological profiles in human populations, both prior to and during MDA programs
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