Mathematical modelling of lymphatic filariasis elimination programmes in India: required duration of mass drug administration and post-treatment level of infection indicators

Abstract

BackgroundIndia has made great progress towards the elimination of lymphatic filariasis. By 2015, most endemic districts had completed at least five annual rounds of mass drug administration (MDA). The next challenge is to determine when MDA can be stopped. We performed a simulation study with the individual-based model LYMFASIM to help clarify this.MethodsWe used a model-variant for Indian settings. We considered different hypotheses on detectability of antigenaemia (Ag) in relation to underlying adult worm burden, choosing the most likely hypothesis by comparing the model predicted association between community-level microfilaraemia (Mf) and antigenaemia (Ag) prevalence levels to observed data (collated from literature). Next, we estimated how long MDA must be continued in order to achieve elimination in different transmission settings and what Mf and Ag prevalence may still remain 1 year after the last required MDA round. The robustness of key-outcomes was assessed in a sensitivity analysis.ResultsOur model matched observed data qualitatively well when we assumed an Ag detection rate of 50 % for single worm infections, which increases with the number of adult worms (modelled by relating detection to the presence of female worms). The required duration of annual MDA increased with higher baseline endemicity and lower coverage (varying between 2 and 12 rounds), while the remaining residual infection 1 year after the last required treatment declined with transmission intensity. For low and high transmission settings, the median residual infection levels were 1.0 % and 0.4 % (Mf prevalence in the 5+ population), and 3.5 % and 2.0 % (Ag prevalence in 6–7 year-old children).ConclusionTo achieve elimination in high transmission settings, MDA must be continued longer and infection levels must be reduced to lower levels than in low-endemic communities. Although our simulations were for Indian settings, qualitatively similar patterns are also expected in other areas. This should be taken into account in decision algorithms to define whether MDA can be interrupted. Transmission assessment surveys should ideally be targeted to communities with the highest pre-control transmission levels, to minimize the risk of programme failure.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1768-y) contains supplementary material, which is available to authorized users.

Persistent ‘hotspots’ of lymphatic filariasis microfilaraemia despite 14 years of mass drug administration in Ghana

“…2,6,7 However, studies have shown that in areas with high mf prevalence, more than six rounds of MDA were required to achieve interruption with low epidemiological coverage. 10,19 Other factors that may be responsible for the delay in mf interruption of transmission in high prevalent areas include poor compliance. 8 In this study, there seemed to be no differences in the reported MDA epidemiological coverage.…”

Improving the efficacy of a prophylactic vaccine formulation against lymphatic filariasis

“…Treatment with drugs alone is not effective as a prophylaxis against LF. There is a need for a more sustained approach such as a prophylactic vaccination to stop transmission and eliminate LF from the endemic areas (Dakshinamoorthy et al 2013c; Jambulingam et al 2016; Harris et al 2017). Our laboratory and others have identified several potential vaccine antigens that are shown to confer significant protection against challenge infections in experimental animals (Samykutty et al 2010; Dakshinamoorthy et al 2013b, Dakshinamoorthy et al 2013c; Arumugam et al 2014).…”

Determinants of transmission hotspots and filarial infection in households after eight rounds of mass drug administration in India

“…Assuming these are applicable to our study area it may be seen that though both hotspots and non‐spots recorded same levels of compliance at 55%, a higher proportion of Ag (Mf) positive individuals and positive households were found in hotspots. These observations imply that the dynamics of impact of the MDA in an area may not only be influenced by the baseline endemicity but also by current mosquitogenic conditions prevailing in that area. Therefore, for interrupting transmission wherever appropriate, MDA may be supplemented with localised vector control measures, as indicated by the simulation models: annual MDA with vector control measures will be a better performing strategy in bringing down both human and vector infection well below the recommended thresholds for LF elimination.…”