Associations between infection intensity categories and morbidity prevalence in school-age children are much stronger for Schistosoma haematobium than for S. mansoni

Abstract

Background: World Health Organization (WHO) guidelines for measuring global progress in schistosomiasis control classify individuals with Schistosoma spp. infections based on the concentration of excreted eggs. We assessed the associations between WHO infection intensity categories and morbidity prevalence for selected S. haematobium and S. mansoni morbidities in school-age children.

Methodology: A total of 22,488 children aged 6-15 years from monitoring and evaluation cohorts in Burkina Faso, Mali, Niger, Uganda, Tanzania, and Zambia from 2003-2008 were analyzed using Bayesian logistic regression. Models were utilized to evaluate associations between intensity categories and the prevalence of any urinary bladder lesion, any upper urinary tract lesion, microhematuria, and pain while urinating (for S. haematobium) and irregular hepatic ultrasound image pattern (C-F), enlarged portal vein, laboratory-confirmed diarrhea, and self-reported diarrhea (for S. mansoni) across participants with infection and morbidity data.

Principal findings: S. haematobium infection intensity categories possessed consistent morbidity prevalence across surveys for multiple morbidities and participants with light infections had elevated morbidity levels, compared to negative participants. Conversely, S. mansoni infection intensity categories lacked association with prevalence of the morbidity measures assessed.

Conclusions/significance: Current status infection intensity categories for S. haematobium were associated with morbidity levels in school-age children, suggesting urogenital schistosomiasis morbidity can be predicted by an individual's intensity category. Conversely, S. mansoni infection intensity categories were not consistently indicative of childhood morbidity at baseline or during the first two years of a preventive chemotherapy control program.

Fig 1. Line graphs of the percentage of 6- to 15-year-old children who were Schistosoma infection and heavy-intensity positive (row A), S. haematobium morbidity positive (row B), and S. mansoni morbidity positive (row C) at each survey year (baseline, BL; follow-up 1, FU1; follow-up 2, FU2).

S. haematobium estimates are from Mali, Niger, and Tanzania and are assessed by urine filtration. S. mansoni estimates are from Mali, Niger, Tanzania, and Uganda and are assessed by the Kato-Katz technique.

Fig 2. Line graphs of Schistosoma haematobium-related morbidity percentages, broken down by intensity category, across three surveys (baseline, BL; follow-up 1, FU1; follow-up 2, FU2).

Participants were enrolled between 2003 and 2008 in Mali, Niger, and Tanzania. Clustering by school accounted for in 95% confidence bands. Infections were assessed by urine filtration.

Fig 3. Line graphs of Schistosoma mansoni-related morbidity percentages, broken down by intensity category, across three surveys (baseline, BL; follow-up 1, FU1; follow-up 2, FU2).

Participants were enrolled between 2003 and 2008 in Mali, Niger, Tanzania, and Uganda. Clustering by school accounted for in 95% confidence bands. Infections were assessed by Kato-Katz stool examination.

Fig 4. Modification of Fig 3 where participants’ Schistosoma mansoni intensity is split into three categories: 0 EPG, 1–199 EPG, and ≥200 EPG.

See Fig 3 description for more details. Data are from three surveys (baseline, BL; follow-up 1, FU1; follow-up 2, FU2).