WHO launched the GPELF in 2000 in response to World Health Assembly resolution WHA50.29, which urged Member States to initiate activities to eliminate lymphatic filariasis (LF) as a public health problem, a goal subsequently targeted for 2020. This “global elimination of LF as a public health problem” has been operationally interpreted as the reduction in the prevalence of infection with Wuchereria bancrofti, Brugia malayi, or Brugia timori in all endemic countries to target thresholds below which transmission of the infection cannot be sustained. These thresholds were earlier empirically observed to be less than 1.7% microfilaria (mf) prevalence for Bancroftian filariasis and less than 1.5% mf prevalence for Brugian filariasis [3], though current targets for GPELF are considerably more conservative [4]. In line with its first strategic plan [5], the GPELF has two principal aims: (i) to interrupt LF transmission, and (ii) to manage morbidity and prevent disability [6] (Fig. 1). In 2010, WHO published the GPELF's progress report from its first ten years and a new strategic plan outlining the approach and relevant milestones for its second ten years [2]. The report defines the strategic objective of each of GPELF's two aims as follows:

Interrupting transmission—i.e., providing access to mass drug administration (MDA) for every eligible person in endemic areas where mapping results indicate an infection of greater than or equal to 1%. The main strategy to interrupt transmission for the GPELF is MDA using combinations of two filaricidal medicines (albendazole plus either diethylcarbamazine or ivermectin) delivered once-yearly to entire eligible populations in endemic areas. The MDA aims to reduce microfilaraemia in the blood of infected persons to levels that can no longer sustain transmission of LF by mosquito vectors to new hosts. It should be implemented annually for at least five years, which is generally considered to be the reproductive lifespan of the adult filarial worms in humans [7]–[9].

Morbidity management and disability prevention—i.e., providing access to basic care for LF-related diseases to every affected person in endemic areas. The principal public health impact of LF results from the impairment and disabilities related to lymphoedema, elephantiasis, and hydrocoele. A minimum package of health care aims to treat suffering from acute disease and to prevent disease progression and further disability [10].

With these two components taken together, the GPELF can be seen as a public health programme that provides access to specific health services—MDA and basic care for LF-related disease—for every person in need, thereby improving health for millions of people worldwide. Since LF is concentrated among the poorest segments of society, it is clear that GPELF is also a programme effectively promoting health equity and poverty reduction, in full alignment with the globally accepted Millenium Development Goals [11],[12].

Since the publication of GPELF's most recent strategic plan with its clear objectives and milestones towards the attainment of its global elimination goal by 2020 [2], WHO has issued important position statements, technical and policy documents, and guidelines based on newly acquired evidence and updated tools, in order to offer clear guidance to programme managers responsible for LF and other neglected tropical diseases (NTDs). Together, these guidelines provide a common policy framework for the GPELF that each endemic country can rely on to carry out the programmatic steps of its strategic plan en route to achieving elimination at national and regional level (Box 1).

The GPELF is now part of integrated efforts to prevent and treat NTDs, in which MDA, VC. and morbidity management are increasingly integrated and delivered as multi-intervention packages at the global, national, and local levels (Fig. 2) [8], [13], [29], [30].

Interrupting LF transmission through MDA and other forms of preventive chemotherapy (PC) is being achieved in collaboration with other NTD programmes [29]–[32]. For example, national LF programmes are now being integrated with those for preventive chemotherapy to control or eliminate onchocerciasis, schistosomiasis, soil-transmitted helminthiasis, and blinding trachoma. This focus on integration is based on the recognition that these diseases are often coendemic and that the programmes targeting them share many common activities—including once- or twice-yearly treatment, advocacy, social mobilization, training of health workers, monitoring treatment coverage, and evaluating outcomes of the interventions—that can be coimplemented. Integrated preventive chemotherapy approaches save costs by optimizing the use of resources across multiple programmes [32], [33].

MMDP activities likely can also benefit from integrated approaches that involve other disease programmes, since the minimum package of care for lymphedema or elephantiasis can address not only LF-related cases but also individuals whose lymphedema or elephantiasis is related to other, non-LF, conditions that affect skin integrity. Possible partners for integration of MMDP activities include programmes focusing on chronic disease, such as those to control leprosy, podoconiosis, diabetes, and Buruli ulcer [10]. Since the basics of the recommended management—skin care, elevation, exercise, and hygiene—are common to all these conditions, regardless of the etiology, integrating management of lymphedema or elephantiasis with that of other chronic diseases requiring long-term care should be both feasible and cost-effective [34]. Even for hydrocoele, a focus on integration could be used to help improve general surgical activities in hospital both qualitatively and quantitatively [22], [35], [36].

It is also essential to recognize that endemic communities will require MMDP beyond MDA, post-MDA surveillance, and even verification of interruption of transmission, since the pathology and damage left behind by the infection will persist for many years. Therefore, GPELF ultimately aims to integrate services for the management of LF morbidity and the prevention of disability fully into national health systems by training health staff to care for these patients, by building on referral mechanisms from community to health worker to specialist and back, and by exploring potential subsidies to help with the cost of treatment [21].

For VC too, Integrated Vector Management (IVM) has now become a recommended strategy across programmes targeting control, elimination or eradication of vector-borne diseases [37]. IVM is defined as a “rational decision-making process for the optimal use of resources for vector control.” The aim is to make a significant contribution to the prevention and control of vector-borne diseases, by marrying conventional single-intervention strategies and promoting multisector approaches to achieve targets cost effectively and promote sustainability. A WHO-published Position Statement on IVM to control malaria and LF [38] recommends implementation of VC as a multidisease approach in areas coendemic for both diseases and where the vectors of malaria and LF are both affected by the same VC interventions (e.g., insecticide-treated mosquito nets, indoor residual spraying, larval control). These recommendations are based on the overlapping geographical distribution of LF and malaria and the fact that Anopheles mosquitoes transmit both malaria and LF in many endemic areas [14], [15], [39], [40]. Even where LF is transmitted by other types of mosquitoes, VC measures that target malaria may still reduce transmission of both LF and malaria.

The opportunities presented by such intersectoral and integrated approaches hold the promise of developing even greater synergies among elimination programmes for LF and other programmes targeting vector-borne diseases, and of further extending the benefits of the global LF programme to neglected populations who invariably suffer from multiple overlapping diseases linked to poverty [12], [41].

To achieve the Programme's objectives, concerted action will continue to be required. As outlined in the Strategic Plan, key partners must play important roles in helping the national governments and the GPELF overcome its considerable challenges and achieve its global elimination goal [30], specifically the following points:

Together, all these groups form the Global Alliance to Eliminate Lymphatic Filariasis (GAELF), founded in 2000, which aims to coordinate partners and political, financial, and technical support for the GPELF, and engage in advocacy and fundraising to assist the national programmes [2].

Fig. 3 demonstrates schematically the extensive partnership supporting the GPELF. Moving forward, all partners will need to coordinate not only among themselves but also with other sectors to ensure the most cost-effective and rational use of resources in support of the elimination of LF.

In 1999, WHO established the LF Technical Advisory Group (TAG) to provide expert advice to the GPELF and the LF Programme Review Group (PRG) to monitor the country progress and to address specific technical issues. The PRG was subsequently decentralized to the LF Regional Programme Review Group (RPRG) in 2002 [43]. STAG-NTDs was established in 2007 as the principal advisory group to WHO on overall global policies and strategies for elimination and/or control of NTDs including LF, and, especially, through its working groups, assumed the earlier function of the LF TAG [44]. National programmes now submit annual reports on drug coverage and impact of MDA to WHO, and the results are published in the WHO's PCT Databank that is updated regularly [45]. These independent technical review groups monitor reported data and provide guidance to national programmes. Additionally, these groups review operational research findings to identify the need for new guidelines or modification of current ones.

WHO recommends that all Member States where lymphatic filariasis is endemic be part of the proposed strategy that aims to reach the elimination goal by 2020. Between the beginning of GPELF in 2000 and 2012, 59 countries have started implementing MDA, and 12 countries have successfully stopped MDA after five or more rounds with high coverage and entered the post-MDA surveillance phase. Of the remaining countries, all 14 will implement and complete LF mapping by the end of 2015.

Through the tremendous efforts of national programmes, GPELF had by 2012 realized the cumulative delivery of more than 3.9 billion doses of medicines to 952 million people covered by MDA worldwide since GPELF was launched in 2000, out of 1.39 billion people in need of treatment [1]. In 2011 alone, over 500 million people were reached; i.e., roughly one in seven persons in the world was receiving MDA targeting lymphatic filariasis. GPELF is recognized as one of the most rapidly expanding global health programmes in public health history and is a remarkable story of partnership where all involved Member States and partners work together aiming at one common goal to achieve remarkable health and economic impact [1], [46], [47].

The GPELF Strategic Plan sets 2014 as the target date for all endemic countries to start MDA, 2016 to achieve full geographic coverage, and 2020 to move to post-MDA surveillance [2]. Within an endemic country, because endemicity is defined and MDA activities implemented at the subnational implementation unit level (usually a health district), at the country level implementation activities begin gradually across districts [30], [32], [48]. Consequently, districts within a country can move along the programme steps at varied rates, and large countries with a greater number of districts require a longer time than small countries, to reach the shared global elimination goal. Taking into account country progress with MDA in each endemic country since 2000 and the size of the population requiring MDA, and assuming that each implementation unit stops MDA after five rounds, the number of individuals needed to be targeted by MDA every year up to the 2020 elimination goal has been projected and updated annually [45]. These optimistic projections of country progress are based on the assumption that each country will be verified for interruption of transmission after five years of post-MDA surveillance.

Fig. 4 illustrates the broad view of MDA progress and projection by programme steps from 2000 to 2021, whereas Fig. 5 presents in global maps the country-wide MDA progress and projection by programme steps for the same time period. The first decade of GPELF can be seen to be characterized by rapid scaling up of mapping and MDA; since then, a number of countries have already successfully moved entirely through post-MDA surveillance. In addition, nine out of 81 countries originally identified as endemic at the start of GPELF were reclassified as nonendemic by STAG-NTDs and its working group after review in 2010.

Intensified activities in the next five years will be essential to achieve the global elimination goal by 2020; concerted efforts of the Member States and partners will be required to accelerate (i) completion of mapping and rapid scale-up of MDA in slow-starter and high-burden countries, especially in the African Region, and (ii) progressive implementation of TAS, stopping of MDA and phasing in post-MDA surveillance across the Regions. With this time table, the world should see the final rounds of MDA in 2020—and thus global interruption of transmission of lymphatic filariasis by 2021, even though “verification” of this interruption will still await completion of the post-MDA surveillance in the late-starting countries.