Rapid diagnostic testing for onchocerciasis in Maridi (South Sudan) before and after improving elimination strategies: a repeated cross-sectional survey

Amber Hadermann; Stephen Raimon Jada; Luís-Jorge Amaral; Robert Colebunders; Yak Yak Bol; Joseph N Siewe Fodjo

doi:10.12688/openreseurope.16093.2

Rapid diagnostic testing for onchocerciasis in Maridi (South Sudan) before and after improving elimination strategies: a repeated cross-sectional survey

Open Res Eur. 2024 Mar 22:3:206. doi: 10.12688/openreseurope.16093.2. eCollection 2023.

Authors

Amber Hadermann¹, Stephen Raimon Jada², Luís-Jorge Amaral¹, Robert Colebunders¹, Yak Yak Bol³, Joseph N Siewe Fodjo¹

Affiliations

¹ Global Health Institute, University of Antwerp, Antwerp, Flanders, 2610, Belgium.
² Amref Health Africa South Sudan, Juba, South Sudan.
³ Neglected Tropical Diseases Programme, Ministry of Health, Juba, South Sudan.

Abstract

Background: Maridi County is an onchocerciasis-endemic area in South Sudan. Annual community-directed treatment with ivermectin (CDTi) was instituted in Maridi since the early 2000s, but with low coverage. In 2021, the CDTi programme was strengthened to a six-monthly programme. Additionally, the community-based vector control strategy "Slash and Clear" has been implemented since 2019 at the Maridi Dam, the only blackfly breeding site in the area. This study assessed the effect of these reinforced onchocerciasis elimination interventions on the Onchocerca volvulus seroprevalence among young children, an indicator of ongoing transmission.

Methods: Baseline and follow-up serosurveys were conducted in Maridi in 2019 (prior to strengthening onchocerciasis elimination efforts) and 2023, respectively. During both surveys, children aged three to nine years were recruited from five study sites situated at different distances from the Maridi Dam. Ov16 antibodies were detected via rapid diagnostic tests (RDTs) using whole blood obtained by finger-pricking the participants. Baseline and follow-up Ov16 prevalence rates were calculated and compared.

Results: In 2019, the Ov16 seroprevalence among children aged three to nine years was 24.5% compared to 30.6% in 2023 (p=0.22). Both surveys found a particularly high Ov16 seroprevalence in the study site closest to the Maridi Dam (35.0% in 2019 and 44.0% in 2023, p=0.52). The Ov16 seroprevalence had a non-significant decreasing trend in the three-year-old children, from 12.5% (3/24) in 2019 to 8.8% (3/34) in 2023 (p=0.65).

Conclusion: The persistent Ov16 RDT seropositivity among three-year-old children in 2023 indicates ongoing O. volvulus transmission. Therefore, further strengthening of the onchocerciasis elimination programme is required. The study highlights the utility of RDTs in monitoring onchocerciasis transmission in highly endemic settings.

Keywords: Onchocerca volvulus; Onchocerciasis; antibodies; children; ivermectin; seroprevalence; testing; transmission; vector control.

Grants and funding

RC received funding from the European Research Council, grant number 768815 and FIND. L-JA had funding from La Caixa Foundation, grant number B005782. JNSF and RC received funding from the Research Foundation – Flanders (FWO), grant number: 1296723N and G0A0522N, respectively. The funders had no role in the study design, data collection and analysis, decision to publish, or manuscript preparation.