Evaluating the Evidence for Lymphatic Filariasis Elimination

Emma L Davis,Lisa J Reimer,Lorenzo Pellis,T Deirdre Hollingsworth

doi:10.1016/j.pt.2019.08.003

Abstract

In the global drive for elimination of lymphatic filariasis (LF), 15 countries have achieved validation of elimination as a public health problem (EPHP). Recent empirical evidence has demonstrated that EPHP does not always lead to elimination of transmission (EOT). Here we show how the probability of elimination explicitly depends on key biological parameters, many of which have been poorly characterized, leading to a poor evidence base for the elimination threshold. As more countries progress towards EPHP it is essential that this process is well-informed, as prematurely halting treatment and surveillance programs could pose a serious threat to global progress. We highlight that refinement of the weak empirical evidence base is vital to understand drivers of elimination and inform long-term policy.

Highlights

As indicated by the name of the Transmission assessment surveys (TAS), it was hoped that reaching these targets would lead to elimination of transmission (EOT) in most areas
Analysis of the evidence for key biological determinants suggests that a target threshold of
Infection from vector to human is governed by the number of infectious bloodmeals one mosquito will take – calculated from vector survival and competence, extrinsic incubation period (EIP) and blood feeding rate (BFR) – and the probability one infectious bite will result in a viable infection

Summary

Introduction

As indicated by the name of the TAS, it was hoped that reaching these targets would lead to elimination of transmission (EOT) in most areas. Assuming for simplicity that TAS is able to measure a true mf prevalence of less than 1%, this theory of stochastic extinction can be used to estimate how the future probability of EOT (zero cases) depends on a range of setting- and disease-specific variables. Others, such as the probability an infectious mosquito bite results in a viable human infection, have the potential to be more consistent across settings, but currently lack in experimental evidence.

Results

Conclusion