Pre-TAS Evaluation of mass drug administration effectiveness on lymphatic filariasis elimination and study of Immunological response in elephantiasis patients in Osun State, Nigeria
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The need to meet the World Health Organization 2030 target for elimination of lymphatic Filariasis necessitates various activities such as mass administration of medicines (MAM), pre-transmission assessment surveys (pre-TAS)/ epidemiological monitoring survey (EMS) and transmission assessment survey. However for this study, pre-TAS/EMS was conducted to validate elimination milestones and elucidate the lingering immunological consequences of chronic infection. This study conducted a comprehensive evaluation across twelve Local Government Areas (LGAs) in Osun State, screening,7388 individuals for circulating filarial antigen (CFA) using Abbott Filarial Test Strips (FTS), while simultaneously investigating immune modulation in patients with clinical elephantiasis through detailed haematological profiling. Results indicated that the prevalence of the disease at sentinel and spot check sites have been lowered below threshold levels thereby qualifying for a first transmission assessment survey (TAS1) , evidenced by a 0% antigenemia rate across all surveyed LGAs, a figure significantly below the World Health Organization’s <2% threshold. . The average percentage of individual participation in MDA/MAM programs was found to be 56.09%, whereby, Ola-Oluwa LGA recorded the highest at 84.70% while the list MDA program participation was found at Ilesha East with 18.97%, highlighting a potential vulnerability in vector control compliance. Furthermore, haematological assessments of chronic cases revealed a distinct state of immune suppression, characterized by significant reductions in total white blood cell and lymphocyte counts, alongside persistent monocytosis and eosinopenia. These findings suggest that while Osun State has successfully transitioned into a post-transmission phase, the lingering physiological impacts on the chronically ill and the moderate rates of preventive practice necessitate sustained surveillance and enhanced public health interventions to ensure permanent disease eradication
Author Summary
Lymphatic filariasis (LF) is a debilitating neglected tropical disease primarily caused by Wuchereria bancrofti and transmitted by mosquitoes, leading to chronic physical deformities such as elephantiasis. Although global infections have decreased, LF remains a critical public health concern across Africa. Nigeria reports a national prevalence rate of 11.18%, with the South West zone contributing 1.26%. Prior regional surveys in Osun State documented a 1.7% circulating filarial antigen (CFA) prevalence, highlighting the necessity of systematic mass drug administration (MDA) and continuous post-intervention monitoring.
To assess transmission interruption and host immunological status, this study screened 7,388 individuals across 12 Local Government Areas (LGAs) in Osun State using Abbott Filarial Test Strips (FTS). Results revealed a 0% CFA prevalence across all 24 sentinel and spot-check sites, successfully meeting the World Health Organization threshold (<2%) to qualify the region for its first Transmission Assessment Survey (TAS1). Survey metrics demonstrated an average MDA participation rate of 56.09%, whereas long-lasting insecticidal net (LLIN) compliance averaged significantly lower at 41.09%. These findings confirm the interruption of active LF transmission while emphasizing the necessity of sustained post-MDA surveillance to prevent disease resurgence.
