Prospects for the Control of Neglected Tropical Diseases by Mass Drug Administration

Henk L. Smits

Disclosures

Expert Rev Anti Infect Ther. 2009;7(1):37-56. 

In This Article

Abstract and Disease Burden & Poverty Control

Abstract

The prospects for the control of neglected tropical diseases, including soil-transmitted helminthiasis, shistosomiasis, lymphatic filariasis, onchocerciasis and trachoma, through mass drug administration, are exemplified by the elimination of the trachoma as a public-health problem in Morocco. In spite of this and other striking successes, mass drug administration programs are faced with major challenges resulting from suboptimal coverage and lack of efficacy. At current suboptimal coverage rates, programs may need prolongation for an extended period, increasing costs and undermining sustainability. Community participation through health education and information appears to be crucial to improve coverage and to achieve sustainability. Implementation of complementary measures, such as vector control, improved hygiene and environmental sanitation, are important to further control transmission and to prevent re-emergence of the infection and, again, may only be achieved effectively through community-based initiatives. To reduce costs and to relieve pressure on the health system, combining neglected tropical disease programs in areas where diseases coexist and integration with existing control programs for malaria, tuberculosis and HIV/AIDS is advocated. The risk of developing drug resistance is of particular concern in view of the lack of alternative drugs, and reduced treatment efficacy due to emerging resistance is evident for the soil-transmitted helminths and onchocerciasis. Given the risk for the development of drug resistance and the need for a high degree of participation, close attention should be paid to the monitoring of the coverage and efficacy of the different program components.

Disease Burden and Poverty Control

The WHO estimated that, in 2002, the world-wide burden of disease according to the disability-adjusted life years (DALYs) due to infectious diseases was as high as 457.7 million. Respiratory tract infections have the highest toll on health, accounting for almost 21% of the disease burden due to infectious diseases. Other significant contributors to the disease burden are HIV/AIDS (19%), malaria (9%) and tuberculosis (TB, 8%), diseases that receive much attention also in terms of financial resources for research and prevention. Vaccine-preventable childhood infections (11%) and diarrheal diseases (14%), largely preventable by the provision of clean water, obeying food hygiene and sanitation, are of equal importance. According to the WHO 2002 estimates, the group of so-called neglected tropical diseases (NTDs), which include, among others, the soil-transmitted helminths (STH), schistosomiasis, lymphatic filariasis (LF), onchocerciasis and trachoma, contribute to approximately 5% of the global disease burden due to infectious diseases Table 1 .[1] While NTDs are believed to collectively cause the death of over half a million people annually, their impact on public health stems largely from disability and morbidity, sometimes affecting a major proportion of the population in endemic areas.[2] The burden of disease due to NTDs may well have been underestimated, as subtle but often chronic disease manifestations that may not be easily recognized owing to lack of appropriate diagnostic tools or epidemiological information are perceived to have a profound impact on well being and proper functioning in society. A reassessment of the morbidity due to STH led to an increase in the DALYs from 4.7 million, as estimated by the WHO, to 39 million, or almost 8% of the disease burden due to infectious diseases, as estimated in a study by Hotez and coworkers.[3] The impact of other NTDs may have been underestimated as well; the clinical manifestations are easily overlooked and, hence, these diseases are often under-reported. For example, the impact of schistosomiasis in Asia appears to be much higher than previously estimated.[4]

Some of the NTDs, such as STH, have a severe economic impact in almost all developing countries, while others, such as schistosomiasis, onchocerciasis and LF, are more confined to specific regions and countries where they have a deep impact on society. As these NTDs are largely preventable, it is increasingly recognized that their control is a major strategy to reduce poverty by improving educational outcomes and worker productivity.[5] For five of the NTDs with a total burden of disease with 52.1 million DALYs, or 11% of the total disease burden due to infectious diseases, control programs have been initiated based on community-wide drug administration to at-risk populations.[6,7] These five NTDs are STH, schistosomiasis, LF, onchocerciasis and trachoma, and their control is considered to be highly cost-effective, particularly, when control efforts are combined in areas where diseases coexist.[8]

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