Seroprevalence of onchocerciasis in Ogun State, Nigeria after ten years of mass drug administration with ivermectin

Background: This serological study conducted between March and July 2015 investigated the status of onchocerciasis in Ogun State, Nigeria after a decade of mass drug administration (MDA) with ivermectin. Baseline information from the rapid epidemiological mapping of onchocerciasis (REMO) prior to MDA had indicated that Ogun State was meso-endemic to onchocerciasis. Following years of treatment with ivermectin, it has become important to investigate the current status of the disease using more sensitive diagnostic methods. Methods: The study was conducted in 32 communities in eight onchocerciasis-endemic local government areas (LGAs). Using the Ov16 rapid diagnostic test (Ov16 RDT), finger-prick whole blood was obtained from 3 895 consented participants from age five and above. Skin snips were obtained from a subset of 481 corresponding participants as the majority of community members did not consent to skin snipping. Results: Study revealed a cumulative seroprevalence of 9.3% (CI 9.29-9.31%) by RDT and 17.3% (CI 16.73-18.34%) microfilaridermia prevalence by the skin snip subset. Seroprevalence among children between the ages of five and nine was 2.9% (CI 1.74-3.53%) across all LGAs. A community microfilaria load (CMFL) between 0 and 1.21 MF/skin snip was recorded in the different communities studied. Among the studied LGAs, children in Odeda LGA recorded the highest seroprevalence by RDT (14.9%) followed by Abeokuta North (5.1%), Abeokuta South (4.8%) and Imeko-Afon (0.6%), while Ewekoro, Ifo, Obafemi-Owode and Yewa North LGAs recorded zero prevalence. Conclusion: It appears that the elimination of onchocerciasis in some LGAs is possible considering the lack of new infection among children and the hypo-endemicity among the adult population. However, the microfilaria prevalence observed among adults is of concern as it may imply that mass treatment has not been effective. Increased therapeutic coverage is advised to fully maximise the potential of ivermectin treatment to achieve the disease elimination.