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

Expert Commentary

The goal of MDA programs is to eliminate disease as a public-health problem by reducing diseases prevalence rates to a level that will interrupt transmission and that will make re-emergence of the disease unlikely. The almost complete disappearance of LF after MDA from several countries, including some African countries, and the successful control of trachoma in Morocco have clearly demonstrated that the control of these NTDs is also possible in resource-poor communities in developing countries. However, it has become increasingly clear that delivery of MDA to all target groups may not be easily achieved due to lack of funding and/or infrastructure. In addition, programs suffer from suboptimal coverage and the consensus is that, at current coverage rates, prolongation of treatment with additional rounds of MDA during additional years is needed or that MDA should be intensified and administered more frequently. Coverage may be improved by strengthening health education and stimulating community participation. Research is needed to determine optimal strategies to improve coverage of MDA under different cultural conditions. The implementation of complementary program measures, such as vector control, improved hygiene and environmental sanitation, which aim to remove factors that contribute to the transmission of the pathogens, is essential for a prolonged effect of MDA and to prevent re-emergence of the disease. Studies are needed to address the efficacy of these measures and their optimal delivery in resource-poor communities. The implementation of a quality system could be another means to improve efficacy by improving and adjusting measures at an early stage.[195] Geographical information systems and remote sensing are important tools to understand the ecology and epidemiology of neglected diseases, to help to identify target populations and to assess the efficacy of the MDA control measures.[196,197]

The development of reduced drug sensitivity or even resistance is of major concern because alternative drugs for MDA are not able to respond to drug resistance should it occur. However, evidence that altered drug sensitivity plays a role in the observed suboptimal effect of MDA is weak but, with the extension of programs and increased drug pressure, it could become an important issue, particularly in the cases of onchocerciasis owing to the use of a single drug in combination with the very long lifespan of the adult female worms and in the cases of STH and LF owing to the simple mechanism by which resistance to ALB is developed ( Table 3 ) . With the progression of the different programs, the implementation of effective monitoring systems for MDA efficacy will be crucial and a shift to targeted case detection and treatment may be needed in order to eliminate foci of transmission and to identify emerging drug-resistance at an early stage. Unfortunately, viable alternatives to current MDA programs are not readily available. However, drug-discovery programs for some of the NTDs have yielded promising compounds that may be developed into effective drugs.[198] Vaccine developments are, at best, still at the stage of basic research.[199,200,201,202,203,204,205,206]

Mass drug administration takes a high toll on the limited capacity of the health services. In addition, interest in the control of NTDs will lessen when their prevalence becomes lower and, hence, programs may become unsustainable when the target is within reach. Therefore, at this stage, combination of MDA programs in areas where NTDs overlap appears to be the main strategy to reduce costs and to ensure sustainability. Integration with control programs for the major tropical infectious diseases, such as malaria, including combination of MDA for NTDs with bednet programs, is an option to consider.[207,208] MDA programs also could be merged with immunization activities.

The persistence of remaining foci of infection of Guinea worm in nomadic tribes in some remote areas in Africa illustrates the fact that these diseases are less easily controlled in these more-vulnerable and often marginalized communities. Disease may re-emerge from such communities and, therefore, specific efforts should be undertaken to reach these communities. Less-accessible groups, such as nomadic tribes or children that do not attend school, may be affected more severely. In particular, in countries or areas with low education participation, inclusion of such groups is important. However, delivering healthcare to people with a low level of literacy can be problematic, even if this comprises simple messages or measures.[209] Therefore, special programs to address such groups should be developed.

Finally, there is an urgent need for control programs for other NTDs, such as strongyloidiasis, Chagas disease, human African trypanosomiasis, leishmaniasis and Buruli ulcer. Patients with strongyloidiasis may profit from IVM administration[210,211] and miltefosine, a new drug for visceral leishmaniasis, potentially could be used in MDA.[212,213] Patients with some of these other NTDs could benefit from health education, vector control or the use of bednets as well. However, the development of affordable drugs and vaccines remains of utmost importance for the effective control of these diseases.

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