Rapid assessment of Loa loa prevalence and its implications on onchocerciasis and lymphatic filariasis elimination programmes in Osun state, Nigeria

Abstract Loiasis remains a significant public health concern, particularly in regions co-endemic for onchocerciasis and lymphatic filariasis, where high Loa loa microfilaraemia increases the risk of Severe Adverse Events (SAE) following mass drug administration of ivermectin. This study evaluated loiasis prevalence and associated SAE risk in Osun State, Nigeria, where long-term mass drug administration is being implemented. The study employed the Rapid Assessment Procedure for Loiasis (RAPLOA) and this was conducted in nine communities across three Local Government Areas (LGAs) of Osun State. A total of 720 individuals were interviewed using an individual-level questionnaire to obtain history of eye worm. Data were analysed to determine prevalence estimates and risk classifications were determined using African Programme for Onchocerciasis Control (APOC) thresholds, while age-related association were analysed using Chi-square and linear trend tests. A total of 59 (8.2%) of participants reported having a history of eye worm, indicating low infection rate. Community-level prevalence ranged from 2.50% to 21.25%, with eight communities classified as low risk for SAEs (< 20% RAPLOA prevalence) and one community (Ifetedo) classified as moderate risk. At LGA level, Ife-South recorded the highest prevalence, accounting for 12.1% of participants, followed by Ejigbo (6.7%) and Odo-Otin (5.8%). Age-specific analysis showed no significant association ( p > 0.05) between age and infection in Odo-Otin and Ejigbo LGAs or in the pooled dataset, although a significant positive trend with age was observed in Ife-South, suggesting a localized cumulative exposure. This study reveals that loiasis is present but occurs at low endemic levels in these LGAs. The implication of this low endemicity is that ivermectin-based interventions can continue safely, though localized variations in transmission prevalence emphasize the need for periodic community-level reassessments to minimize the risk of severe adverse events during mass treatment campaigns.