Assessing the need to implement mass drug administration against Wuchereria bancrofti infection using both human serology and xenomonitoring in the urban conurbation of Monrovia, Liberia.

Background: Lymphatic filariasis (LF) is a parasitic disease-causing severe pain, disfiguring, and disabling clinical conditions such as lymphoedema and hydrocoele that are associated with morbidity and stigma. The disease has been targeted for global elimination with the annual mass drug administration (MDA) strategy. We have evaluated the need to implement mass drug administration against W. bancrofti infection in urban zones of Monrovia using both serology and molecular Xenomonitoring (XM).

Methodology: Confirmatory mapping protocols recommended by WHO were carried out in the four health districts of Monrovia. Schools were selected using probability proportionate to size (PPS) and eligible children aged 9-14 years were tested for circulating filarial antigen (CFA) using an Alere Filariasis Test Strip (FTS). Health Districts were assessed as requiring MDA if they exceeded the critical cut off of 3 positive tests corresponding to CFA ≥ 2%. Two health districts were selected for entomological investigations based on pre-disposing risk factors for mosquitoes. Mosquito collection was carried out using exit traps (ETs) and gravid trap (GTs) for 6 months. Mosquitos were tested for W. bancrofti DNA using qPCR.

Principal findings: Ninety-six children in the sample had a positive serology test result, with a mean CFA prevalence of 5.3% (95% CI: 4.4 - 6.5%). All four health districts exceeded the critical cut off of 3 cases and in Somalia Drive there were 59 positive tests. In Central Monrovia which had 4 cases, 2 of them are likely locally imported from Somalia Drive where the children reported living. A total of 19,355 potential vector mosquitoes were collected, of which 84.4% (16,335) were Culex and 16.6% (3,020) An. gambiae. All mosquitoes were analyzed, and none were found to be infected with W. bancrofti.

Conclusion: MDA is required in three health districts of Monrovia. Confirmatory mapping protocols require adaptation for urban settings. The sampling strategy for the XM was unable to identify transmission in this case and requires further research to optimise it for informing MDA implementation decisions.