What Is Needed to Eradicate Lymphatic Filariasis? A Model-Based Assessment on the Impact of Scaling Up Mass Drug Administration Programs

Abstract

Background: Lymphatic filariasis (LF) is a neglected tropical disease for which more than a billion people in 73 countries are thought to be at-risk. At a global level, the efforts against LF are designed as an elimination program. However, current efforts appear to aim for elimination in some but not all endemic areas. With the 2020 goal of elimination looming, we set out to develop plausible scale-up scenarios to reach global elimination and eradication. We predict the duration of mass drug administration (MDA) necessary to reach local elimination for a variety of transmission archetypes using an existing model of LF transmission, estimate the number of treatments required for each scenario, and consider implications of rapid scale-up.

Methodology: We have defined four scenarios that differ in their geographic coverage and rate of scale-up. For each scenario, country-specific simulations and calculations were performed that took into account the pre-intervention transmission intensity, the different vector genera, drug regimen, achieved level of population coverage, previous progress toward elimination, and potential programmatic delays due to mapping, operations, and administration.

Principal findings: Our results indicate that eliminating LF by 2020 is unlikely. If MDA programs are drastically scaled up and expanded, the final round of MDA for LF eradication could be delivered in 2028 after 4,159 million treatments. However, if the current rate of scale-up is maintained, the final round of MDA to eradicate LF may not occur until 2050.

Conclusions/significance: Rapid scale-up of MDA will decrease the amount of time and treatments required to reach LF eradication. It may also propel the program towards success, as the risk of failure is likely to increase with extended program duration.

Fig 1. Cumulative number of treatments by year.

The line with circular markers represents the global elimination (comparator) scenario. As highlighted in the text boxes, both the global elimination and eradication I scenario are estimated to conclude MDA after 37 years of MDA. Eradication II, the intensified scale-up scenario, sees the last round of MDA to occur by 2032, after 19 years of MDA. Eradication III is estimated to require 15 years of MDA, concluding in 2028.

Fig 2. Maps depicting the final year of MDA per country for the four scenarios.

The global elimination scenario does not include countries that have not yet begun MDA.

Fig 3. Incremental treatment projections by year (global elimination scenario as comparator).

All eradication scenarios see an increase in the number of treatments after 4 years as the result of the imposed delay for countries that have not previously finished mapping or begun MDA. By 2024, the eradication III scenario requires less treatments than the global elimination (comparator) scenario, and from 2028, the eradication II scenario is also projected to require fewer treatments than global elimination.