Confirmatory mapping for lymphatic filariasis a decade after baseline endemicity assessment in highly urbanized settings of Lagos, Nigeria

Abstract

Objectives: We conducted a confirmatory mapping survey to verify previous survey results, which suggested that lymphatic filariasis is endemic in some parts of Lagos State, Nigeria.

Methods: Finger-prick blood samples were collected from 2787 children aged 7-16 years in six local government areas (LGAs) across 153 targeted schools. Circulating filarial antigen (CFA) levels were measured using the filaria test strip, and LGAs were classified as endemic if there were up to three positive cases (d = 3).

Results: Children who tested positive for CFA were detected in all the six endemic LGAs, surpassing the critical cutoff; Surulere (d = 5, 1.36%, 95% confidence interval [CI] 0.5-3.2%), Mushin (d = 9, 1.9%, 95% CI 0.9-3.7%), Kosofe (d = 10, 1.6%, 95% CI 0.8-3.1%), Oshodi (d = 8, 1.6%, 95% CI 0.8-3.3%), Eti-Osa (d = 9, 2.60%, 95% CI 1.3-5.1%), and Ikorodu (d = 14, 3.0%, 95% CI 1.7-5.0%). All children who tested positive for CFA were ivermectin-naïve, and bed net ownership (14, 25.5%, P = 0.39) and use (7, 50.0%, P = 0.85) was low. About 29% (0-44%) of children who tested positive for CFA are likely to have acquired infection locally, and 71% (55.6-100%) could have acquired infection locally or elsewhere.

Conclusions: Our findings underscore the possibilities of local and imported infections and justify the need to reintroduce mass drug administration, optimize delivery of insecticide-treated bed nets, and extend confirmatory mapping to areas previously classified as non-endemic.

Keywords: Confirmatory mapping; Lymphatic filariasis; Mass drug administration; Nigeria, Lagos.