Parasitic Contamination of Nigerian Naira Notes: A Critical Narrative Review of Public Health Risks, Evidence Gaps and Control Implications

Abstract

Nigerian currency is exchanged repeatedly across households, markets, transport systems, food outlets, health facilities and informal workplaces, creating frequent opportunities for deposition and transfer of faecal and environmental material. Studies conducted in several Nigerian cities have repeatedly recovered helminth eggs, protozoan cysts and other parasitic stages from Naira notes, but the public health meaning of these findings is often overstated because detection on a banknote is not equivalent to viability, infectivity or demonstrated transmission. This critical narrative review synthesises Nigerian evidence on parasitic contamination of Naira notes, evaluates the biological plausibility of currency-mediated transmission, examines methodological limitations, and considers implications for hygiene, food safety, currency management and research. Literature published from 2000 to 19 July 2026 was prioritised, with earlier foundational evidence included when needed. Across studies, reported contamination has varied widely, from approximately 14% to above 60%, with recurrent detection of Ascaris lumbricoides, Enterobius vermicularis, hookworm, Trichuris trichiura, Entamoeba histolytica and Giardia species. Dirty, mutilated and intensively circulated notes tend to show higher contamination, and several studies suggest lower contamination on polymer than paper substrates. Nevertheless, the evidence base is dominated by small, cross-sectional convenience samples, inconsistent note-condition classifications, microscopy without molecular confirmation, limited quality control, and near-absence of viability or transfer experiments. Misidentification is a material concern, particularly for morphologically similar cysts, ova and artefacts. The strongest conclusion is therefore that Naira notes are credible markers and potential vehicles of faecal-environmental contamination, not that they are established major causes of parasitic disease. Public health responses should prioritise hand hygiene, safe food handling, avoidance of saliva-assisted counting, improved withdrawal of heavily soiled notes, and targeted risk communication without promoting unnecessary fear of cash. Future studies should combine molecular identification, viability assays, controlled transfer experiments and epidemiological linkage to determine whether contamination translates into infection risk under real Nigerian conditions.