Serological Evaluation of Onchocerciasis and Lymphatic Filariasis Elimination in the Bakoye and Falémé foci, Mali

24 Mar 2020
Housseini Dolo, Yaya I Coulibaly, Moussa Sow, Massitan Dembélé, Salif S Doumbia, Siaka Y Coulibaly, Moussa B Sangare, Ilo Dicko, Abdallah A Diallo, Lamine Soumaoro, Michel E Coulibaly, Dansine Diarra, Robert Colebunders, Thomas B Nutman, Martin Walker, Maria-Gloria Basáñez

Background

In Mali, ivermectin-based onchocerciasis elimination from the Bakoye and Falémé foci, reported in 2009–2012, was a beacon leading to policy shifting from morbidity control to elimination of transmission (EOT). These foci are also endemic for lymphatic filariasis (LF). In 2007–2016 mass ivermectin plus albendazole administration was implemented. We report Ov16 (onchocerciasis) and Wb123 (LF) seroprevalence after 24–25 years of treatment to evaluate if onchocerciasis EOT and LF elimination as a public health problem (EPHP) have been achieved.

Methods

The SD Bioline Onchocerciasis/LF IgG4 biplex rapid diagnostic test (RDT) was used in 2,186 children aged 3–10 years in 13 villages (plus two hamlets) in Bakoye, and 2,270 children in 15 villages (plus one hamlet) in Falémé. In Bakoye, all-age serosurveys were conducted in three historically hyperendemic villages, testing 1,867 individuals aged 3–78 years.

Results

In Bakoye, IgG4 seropositivity was 0.27% (95%CI=0.13–0.60%) for both Ov16 and Wb123 antigens. In Falémé, Ov16 and Wb123 seroprevalence was, respectively, 0.04% (95%CI=0.01–0.25%) and 0.09% (95%CI=0.02–0.32%). Ov16-seropositive children were from historically meso- and hyperendemic villages. Ov16 positivity was <2% in those ≤14 years, increasing to 16% in those ≥40 years. Wb123 seropositivity was <2% in those ≤39 years, reaching 3% in those ≥40 years.

Conclusions

Notwithstanding uncertainty in the biplex RDT sensitivity, Ov16 and Wb123 seroprevalence among children in Bakoye and Falémé appears consistent with EOT (onchocerciasis) and EPHP (LF) since stopping treatment in 2016. The few Ov16-seropositive children should be skin-snip PCR tested and followed up.