Elimination of Neglected Tropical Diseases: Catalytic Investment, Remarkable Success, Unfinished Business

(See the Viewpoints by Wainwright et al on pages 958–64.) Neglected tropical diseases (NTDs) are no longer as neglected as they once were. Originally bundled together for more effective advocacy to address them [1], the 20 diseases now recognized as NTDs by the World Health Organization (WHO) are more properly regarded as diseases of neglected populations or diseases of poverty in tropical regions. Early during the last decade, 5 of the most prevalent NTDs were selected for special attention by WHO and the international community—lymphatic filariasis (LF), trachoma, onchocerciasis, schistosomiasis, and soil-transmitted helminthiasis (STH). All of these diseases can be controlled through preventive chemotherapy (PC), the periodic (eg, annual) treatment of at-risk populations with single doses of medication, without the need for individual diagnosis. PC provides health benefits to affected individuals as well as to communities through reduced transmission and lower incidence of disease. So closely have these 5 diseases been linked with this single intervention that they are known as “PC-NTDs” [2]. However, with the possible exception of onchocerciasis, PC alone is inadequate in most settings to interrupt transmission. Other measures, such as clean water, sanitation, hygiene, and mosquito bed nets are also required. In this issue of Clinical Infectious Diseases, Wainwright and colleagues [3] highlight the role of foreign assistance in catalyzing the remarkable scaling up of efforts to control—and potentially eliminate—these 5 NTDs. Wainwright et al describe key factors responsible for this impressive accomplishment. These include pharmaceutical company donations of safe and effective drugs for PC, now reaching >1 billion people per year [4]; strong leadership by WHO, including a 2012 NTD “roadmap,” around which the global community rallied [5]; an unwavering commitment to global partnerships [6]; effective advocacy; and visionary, catalytic investment in NTDs by the US Congress through the US Agency for International Development, along with major funding from the Bill & Melinda Gates Foundation and the United Kingdom Department for International Development. No less important, but less frequently heralded, are a myriad of crucial decisions by persons in key positions, the dedication of hundreds of thousands of community drug distributors at the local level, relationships of trust and friendship that developed across institutional and international boundaries, extraordinary leadership by national NTD program officers, and a healthy dose of serendipity [7]. Two additional factors that motivate and bind the NTD community together are a belief that eliminating PC-NTDs contributes to social justice [1] and a sincere desire to alleviate NTD-related suffering—that is, compassion [8]. In advance of 2020, the target date for elimination or control of several NTDs, Wainwright et al rightly celebrate the fact that “over the past decade, enormous numbers of people have had their lives improved through these new NTD programs, and the number of age-standardized disability-adjusted life-years is reported to have decreased for each of these NTDs by 13.5% to 45.3% during this time.” Their encouraging and heart-warming report leaves the nonexpert reader with a few questions, however. What exactly does “elimination” signify—and how does it differ from “control” or “elimination as a public health problem”? At times, Wainwright et al seem to use these terms interchangeably. The appearance of “elimination” in the title of the article might suggest to the nonexpert reader that foreign assistance has already resulted in NTD elimination (when the job is not yet completed) or that the goal of disease elimination programs is simply to reduce disease burden. The somewhat ambiguous application of these terms in the article by Wainwright et al reflects how they are currently used within the NTD arena. But it wasn’t always this way. In 1993, the International Task Force for Disease Eradication (ITFDE) considered 90 diseases and concluded that 6—including LF—could be eradicated [9]. By eradication, they meant, precisely, “reduction of the worldwide incidence of a disease to zero as a result of deliberate efforts, obviating the need for further efforts.” Eradication was deemed possible only if certain scientific criteria could be met, including the absence of a significant human reservoir, availability of safe and effective interventions, sensitive diagnostic tools to measure progress, and intensive surveillance to detect recrudescence and confirm success [9, 10]. Smallpox, the only human disease to be successfully eradicated, met all of these criteria. In contrast, efforts to eradicate hookworm in 1907 and yellow fever in 1915 failed. Mass treatment of hookworm-affected populations reduced the intensity of individual infections, but reinfection occurred in the absence of adequate sanitation. In the case of yellow fever, public health officials did not appreciate the importance of the infection in nonhuman primates [9]. The ITFDE also defined elimination. The term refers to reduction in the incidence of an infection or disease to zero in a defined geographic area as a result of deliberate efforts [10]. Somewhere along the line, the more nebulous—and potentially misleading—term “elimination as a public health problem” crept into popular use. In practice, elimination as a public health problem is indistinguishable from disease control, although it implies something more compelling, permanent, and definitive. It is therefore useful for advocacy and fundraising—at least during the early phases of a campaign. To further confuse the picture, in common parlance, “elimination” is a convenient shorthand for “elimination as a public health problem.” What, then, is the goal for the PC-NTDs? For all 5, the current global programmatic goal is elimination as a public health problem, although as Wainwright et al note, the timeline established to meet this target varies, with “LF and trachoma … in the near term (2020), onchocerciasis in the mid-term (largely by 2025), and schistosomiasis and STH in the longer term.” This variation reflects differences in biology (eg, animal reservoirs for schistosomiasis); programmatic experience; effectiveness of allied interventions (eg, the Surgery Antibiotics Facial Environmental strategy for trachoma, which includes surgery for trichiasis, antibiotics, facial cleanliness, and environmental improvement); and the relatively greater efficacy of drugs against lymphatic filariasis [11, 12], onchocerciasis [13], and trachoma [14] than for schistosomiasis [15] and soil-transmitted helminths, especially Trichuris [16]. A “soft” global goal of elimination as a public health problem does not rule out regional elimination of infection or disease, where feasible; indeed, this has already been achieved, for example, for onchocerciasis in several countries in the Americas [17]. Furthermore, the experience gained by achieving global targets for elimination as a public health problem may pave the way for more ambitious goals of infection or disease elimination. In the early stages of an “elimination” campaign, ambiguity serves a purpose. It brings together under a “big tent” partners whose views and ambitions align but do not necessarily converge. As programs mature and some degree of success is realized, however, fissures inevitably emerge, revealing differences in intention, understanding, and degree of commitment for the long haul. Historically, several disease elimination campaigns have faltered at this crucial juncture, when success was declared prematurely and funding ceased [9]. In this regard, the statement by Wainwright et al that success has “not at all diminished the commitment by donors to keep up their work with NTDs” is reassuring. Precisely because of the massive success described by Wainwright et al in reducing disease and improving the health of hundreds of millions of people living in poverty, it is essential that we communicate clearly to donors, ministries of health, and other partners that the task is not yet completed. The search for quick wins, easy exits, and short-term funding cycles is incompatible with successful disease elimination. Creativity and resolve will be needed to even begin PC in areas plagued by chronic conflict and insecurity. In countries where the targets for elimination as a public health problem are met, ongoing vigilance will be essential to detect and respond to recrudescence of infection. The global NTD movement began <20 years ago as a vision shared by a small band of global health zealots. The meteoric growth and success of this movement, chronicled by Wainwright et al, is a testament to the skillful articulation of that vision, which fueled the moral imagination of donors, decision makers, and public health officials alike. It brings to mind the quote attributed to anthropologist Margaret Mead: “Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it’s the only thing that ever has.” Although the task of NTD elimination is not yet finished, it is appropriate to pause, reflect, and celebrate the massive health benefits delivered by PC and the efforts of those who made this achievement possible. Potential conflicts of interest. The authors report no potential conflicts of interest. Both authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.