E Davis4; L J Reimer1; L Pellis2; T D Hollingsworth3;
1 Liverpool School of Tropical Medicine, UK; 2 University of Manchester, UK; 3 University of Oxford, Big Data Institute, UK; 4 University of Warwick, UK
DiscussionIn the global drive for elimination of lymphatic filariasis, 14 countries have brought prevalence below the WHO-specified thresholds for halting mass treatment. These thresholds were set as practical targets with the expectation that reducing prevalence to this level would lead to transmission fading away in most settings. This has been undermined by recent evidence of ongoing transmission in some areas. As more countries cease interventions it is vital that we ensure this process is well-informed, as prematurely halting control programs could pose a serious threat to global targets. There is a strong mathematical and biological basis for the existence of a break-point for lymphatic filariasis: a threshold below which transmission cannot be sustained, but we often neglect to consider that it is possible for stochastic extinction to occur even before this break-point is reached. The probability of lymphatic filariasis elimination, given a particular prevalence (e.g. 1%), can be calculated by considering the probability a chain of transmission will die out, dependent on certain key biological parameters. We use these methods to demonstrate how the probability of elimination explicitly depends on the accuracy of these parameters, many of which have a poor evidence base. We conclude that the existing experimental evidence does not support a high probability of elimination at the current thresholds, partially due to uncertainties in parameters which could be experimentally assessed.