Antigen Positivity Without Infection: Confirmatory Mapping in Children Rules out Lymphatic Filariasis in Loiasis Co-Endemic Settings in Gabon

Precise mapping is essential for guiding lymphatic filariasis (LF) elimination programmes, yet antigen tests in loiasis co-endemic settings must be read with caution because of cross-reactivity. Gabon’s 2015 national mapping flagged 18 of 52 health districts (HDs) as potentially endemic, but that signal needed confirmation before committing populations to mass drug administration (MDA). We surveyed all 18 HDs between July and August 2025, enrolling 6688 children aged 9–14 years from 341 communities and testing them with the STANDARD™ Q Filariasis Antigen Test (QFAT); every QFAT-positive child then underwent nocturnal calibrated thick-smear microscopy and Wb-LDR quantitative PCR (qPCR) on dried blood spots. Thirteen children (0.19%) were QFAT-positive across eight HDs, and 17 of 18 HDs fell below the confirmatory mapping threshold for MDA. None of the thirteen carried Wuchereria bancrofti microfilariae or DNA; microscopy instead identified Loa loa in three and Mansonella perstans in one. MDA for LF is not warranted in the surveyed HDs, and these findings show why antigen results in loiasis co-endemic settings require parasitological or molecular confirmation before any programmatic decision.