Fig 1.
Time of sampling, preventive chemotherapy and number of participating subjects.
The timeline provides an overview of the different 4-monthly sampling points (S1–5) between October 2018 and October 2020, the administration of a single oral dose of albendazole as part of national preventive chemotherapy program and the number of subjects for whom microscopic data was available. We prematurely stopped the study due to the COVID-19 pandemic. As a consequence of this, no subjects were screened during the last two sampling points (June and October 2020). Test results for both microscopic examination and Ab-ELISA (for all Ab-isotypes) throughout the study was available for 66 subjects.
Fig 2.
Soil-transmitted helminth infection dynamics based on duplicate Kato-Katz thick smear.
Panel A illustrates the cumulative prevalence and Panel B the number of positive test results for each of the three STH species (Ascaris: black, Trichuris: red and hookworms: grey). The individual fecal egg counts (FECs; expressed as eggs per gram of stool) for Ascaris, Trichuris and hookworms over the five sample time points are shown in Panels C, D and E, respectively. For ethical reasons, children were treated when they were positive on copromicroscopy. Large scale deworming was implemented between each sampling time points, except between sampling time point 3 and 4 (see Fig 1).
Fig 3.
Anti-AsLungL3 antibody levels in a non-endemic and endemic area.
Serum samples from 91 healthy adult Belgian blood donors and plasma samples of the 66 Ethiopian school children at the start of the study were analysed for anti-Ascaris IgA, IgG1, IgG2, IgG3, IgG4, IgE and IgM levels. The red dashed horizontal line indicates the diagnostic cut-off, which was defined as the mean optical density (OD) observed in the samples from the healthy Belgian blood donors + 3 times the corresponding standard deviation.
Fig 4.
Dynamics of the anti-Ascaris antibody responses.
The figure summarizes the dynamics of the anti-Ascaris antibody responses in the 66 subjects for whom complete Ab-isotype analysis was available at all five sampling points. Panel A illustrates the cumulative prevalence for all seven Ab-isotypes over the study period and copromicroscopy; number of positive test results for Ab-isotypes for which the cumulative prevalence exceeds that of coprology (IgE, IgG1 and IgG4) is shown in Panel B, the individual IgE, IgG1 and IgG4 response are illustrated in Panels C, D and E, respectively. The ‘c’ in Panels C to E represents the cut-off value for the corresponding Ab-ELISA. For ethical reasons, children were treated when they were positive on copromicroscopy. Large scale deworming was implemented between each sampling time points, except between sampling time point 3 and 4 (see Fig 1).
Fig 5.
Individual Ascaris exposure dynamics based on three Ab-isotypes and copromicroscopy.
These heat maps illustrate the dynamics of the anti-Ascaris IgG4, IgG1 and IgE level as well as the results of the copromicroscopy (by means of fecal egg counts (FECs, expressed as eggs per gram of stool)) over the five sampling time points. Green indicates a negative test result (Ab-ELISA: optic density (OD) less than diagnostic cut-off; copromicroscopy: FEC = 0 EPG); yellow represents a low Ab-response (decision cut-off ≤ OD < median OD across all children that tested positive at baseline) or FEC (O < FEC ≤ 588 EPG); red indicates a high Ab-response (OD ≥ median OD across all children that tested positive at baseline) or FEC > 588 EPG). The study participants were ranked based on the OD for IgG4 measured at baseline. For ethical reasons, children were treated when they were positive on copromicroscopy. Large scale deworming was implemented between each sampling time points, except between sampling time point 3 and 4 (see Fig 1).
Fig 6.
Baseline anti-Ascaris IgG4 levels as a predictor for future Ascaris egg excretion.
Association between the anti-Ascaris IgG4 levels at the start of the study (no IgG4 response: OD < diagnostic cut-off; low IgG4 response: diagnostic cut-off ≤ OD < median OD across all children who tested positive for this Ab-isotype; high IgG4 response: OD ≥ median OD across all children who tested positive for this Ab-isotype) and the Ascaris cumulative prevalence based on copromicroscopy (grey line: high IgG4 response, red: low IgG4 response, black: no IgG4 response) (Panel A), the number of positive test results using IgG4 (0: dark green; 1: light green; 2: yellow; 3: orange; 4: red) (Panel B) and the mean FECs (expressed as egg counts per gram of stool (EPG)) (Panel C). For ethical reasons, children were treated when they were positive on copromicroscopy. Large scale deworming was implemented between each sampling time points, except between sampling time point 3 and 4 (see Fig 1).
Fig 7.
Analysis of the potential cross-reactivity due to Trichuris on anti-Ascaris IgG4 levels.
The figure illustrates the association between the anti-Ascaris IgG4 levels (no IgG4 response: OD < diagnostic cut-off; low IgG4 response: diagnostic cut-off ≤ OD < median OD across all children who tested positive for this Ab-isotype; high IgG4 response: OD ≥ median OD across all children who tested positive for this Ab-isotype) and the Trichuris cumulative prevalence based on copromicroscopy (grey line: high IgG4 response, red: low IgG4 response, black: no IgG4 response) (Panel A), the number of IgG4 positive test results (0: dark green; 1: light green; 2: yellow; 3: orange; 4: red; 5: dark red) (Panel B) and the mean FECs (expressed as egg counts per gram of stool (EPG) (Panel C). In this graph we only included subjects that did not test positive at copromicroscopy at any time point, but that tested at least once on Trichuris (n = 26). For ethical reasons, children were treated when they were positive on copromicroscopy. Large scale deworming was implemented between each sampling time points, except between sampling time point 3 and 4 (see Fig 1).